Joe Giacalone

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Courses

Scholarly Contributions

Journals/Publications

• Esman, T., Espley, J., Gruesbeck, J., Verbiscer, A., Giacalone, J., & Halford, A. (2023). Will we find Martian lightning via Schumann resonances?. Frontiers in Astronomy and Space Sciences, 10, 1162624.
• Florinski, V., Alonso, G. J., Giacalone, J., Roux, J., & Opher, M. (2023). Turbulence and Diffusive Transport of Cosmic Rays in the Very Local Interstellar Medium. \apj, 948(1), 66.
• Giacalone, J., Cohen, C., McComas, D., Chen, X., Dayeh, M., Matthaeus, W., Klein, K., Bale, S., Christian, E., Desai, M., Hill, M., Khoo, L., Lario, D., Leske, R., McNutt, R., Mitchell, D., Mitchell, J., Malandraki, O., & Schwadron, N. (2023). Analyses of 0.05-2 MeV Ions Associated with the 2022 February 16 Energetic Storm Particle Event Observed by Parker Solar Probe. \apj, 958(2), 144.
• Jangsher, S., Al-Dweik, A., Iraqi, Y., Pandey, A., & Giacalone, J. (2023). Group Secret Key Generation Using Physical Layer Security for UAV Swarm Communications. IEEE Transactions on Aerospace Electronic Systems, 59(6), 8550-8564.
• Kornbleuth, M., Opher, M., Dialynas, K., Zank, G., Wang, B., Baliukin, I., Gkioulidou, M., Giacalone, J., Izmodenov, V., Sok{\'o\l}, J., & Dayeh, M. (2023). Probing the Length of the Heliospheric Tail with Energetic Neutral Atoms (ENAs) from 0.52 to 80 keV. \apjl, 945(1), L15.
• Kornbleuth, M., Opher, M., Zank, G., Wang, B., Giacalone, J., Gkioulidou, M., & Dialynas, K. (2023). An Anomalous Cosmic-Ray Mediated Termination Shock: Implications for Energetic Neutral Atoms. \apjl, 944(2), L47.
• Liu, W., Kong, X., Guo, F., Zhao, L., Feng, S., Yu, F., Jiang, Z., Chen, Y., & Giacalone, J. (2023). Effects of Coronal Magnetic Field Configuration on Particle Acceleration and Release during the Ground Level Enhancement Events in Solar Cycle 24. \apj, 954(2), 203.
• Malandraki, O., Cohen, C., Giacalone, J., Mitchell, J., Chhiber, R., McComas, D., Rodr{\'\iguez-Pacheco}, J., Wimmer-Schweingruber, R., & Ho, G. (2023). Unexpected energetic particle observations near the Sun by Parker Solar Probe and Solar Orbiter. Physics of Plasmas, 30(5), 050501.
• Malara, F., Perri, S., Giacalone, J., & Zimbardo, G. (2023). Energetic particle dynamics in a simplified model of a solar wind magnetic switchback. \aap, 677, A69.
• Moradi, A., & Giacalone, J. (2023). Pitch-angle Distributions of 0.5-1 GeV Solar Protons Crossing Earth's Orbit: Influence of the Large-scale Turbulent Interplanetary Magnetic Field. \apj, 952(2), 153.
• Opher, M., Richardson, J., Zank, G., Florinski, V., Giacalone, J., Sok{\'o\l}, J. M., Toth, G., Buxner, S., Kornbleuth, M., Gkioulidou, M., Nikoukar, R., Holst, B., Turner, D., Gross, N., Drake, J., Swisdak, M., Dialynas, K., Dayeh, M., Chen, Y., , Zieger, B., et al. (2023). Solar wind with Hydrogen Ion charge Exchange and Large-Scale Dynamics (SHIELD) DRIVE Science Center. Frontiers in Astronomy and Space Sciences, 10, 1143909.
• Perri, S., Prete, G., Zimbardo, G., Trotta, D., Wilson, I., Lario, D., Servidio, S., Valentini, F., & Giacalone, J. (2023). Interpretation of Flat Energy Spectra Upstream of Fast Interplanetary Shocks. \apj, 950(1), 62.
• Raouafi, N., Matteini, L., Squire, J., Badman, S., Velli, M., Klein, K., Chen, C., Matthaeus, W., Szabo, A., Linton, M., Allen, R., Szalay, J., Bruno, R., Decker, R., Akhavan-Tafti, M. .., Agapitov, O., Bale, S., Bandyopadhyay, R., Battams, K., , Ber{\v{c}i\v{c}}, L., et al. (2023). Parker Solar Probe: Four Years of Discoveries at Solar Cycle Minimum. \ssr, 219(1), 8.
• Singh, M., Fraschetti, F., & Giacalone, J. (2023). Electrostatic Plasma Wave Excitations at the Interplanetary Shocks. \apj, 943(1), 16.
• Swisdak, M., Giacalone, J., Drake, J., Opher, M., Zank, G., & Zieger, B. (2023). A Comparison of Particle-in-cell and Hybrid Simulations of the Heliospheric Termination Shock. \apj, 959(1), 4.
• Trotta, D., Horbury, T. S., Lario, D., Vainio, R., Dresing, N., Dimmock, A., Giacalone, J., Hietala, H., Wimmer-Schweingruber, R. F., Berger, L., & Yang, L. (2023). Irregular Proton Injection to High Energies at Interplanetary Shocks. \apjl, 957(2), L13.
• Zimbardo, G., Ying, B., Nistic{\`o}, G., Feng, L., Rodr{\'\iguez-Garc\'\ia}, L., Panasenco, O., Andretta, V., Banerjee, D., Bemporad, A., De Leo, Y., Franci, L., Frassati, F., Habbal, S., Long, D., Magdalenic, J., Mancuso, S., Naletto, G., Perri, S., Romoli, M., , Spadaro, D., et al. (2023). A high-latitude coronal mass ejection observed by a constellation of coronagraphs: Solar Orbiter/Metis, STEREO-A/COR2, and SOHO/LASCO. \aap, 676, A48.
• Chen, X., Giacalone, J., & Guo, F. (2022). Solar Energetic Particle Acceleration at a Spherical Shock with the Shock Normal Angle \{\textbackslashtheta \}\_\{\{B\}\_\{n\}\} Evolving in Space and Time. \apj, 941(1), 23.
• David, L., Fraschetti, F., Giacalone, J., Wimmer-Schweingruber, R. F., Berger, L., & Lario, D. (2022). In Situ Measurement of the Energy Fraction in Suprathermal and Energetic Particles at ACE, Wind, and PSP Interplanetary Shocks. \apj, 928(1), 66.
• Desai, M., Mitchell, D., McComas, D., Drake, J., Phan, T., Szalay, J., Roelof, E., Giacalone, J., Hill, M., Christian, E., Schwadron, N., McNutt, R., Wiedenbeck, M., Joyce, C., Cohen, C., Davis, A., Krimigis, S., Leske, R., Matthaeus, W., , Malandraki, O., et al. (2022). Suprathermal Ion Energy Spectra and Anisotropies near the Heliospheric Current Sheet Crossing Observed by the Parker Solar Probe during Encounter 7. \apj, 927(1), 62.
• Esman, T., Espley, J., Gruesbeck, J., Fowler, C., Xu, S., Elrod, M., Harada, Y., & Giacalone, J. (2022). Martian Ionospheric Magnetic Fluctuations Below 200 km. Journal of Geophysical Research (Space Physics), 127(9), e30470.
• Getachew, T., McComas, D., Joyce, C., Palmerio, E., Christian, E., Cohen, C., Desai, M., Giacalone, J., Hill, M., Matthaeus, W., McNutt, R., Mitchell, D., Mitchell, J., Rankin, J., Roelof, E., Schwadron, N., Szalay, J., Zank, G., Zhao, L. -., , Lynch, B., et al. (2022). PSP/IS\ensuremath{\odot}IS Observation of a Solar Energetic Particle Event Associated with a Streamer Blowout Coronal Mass Ejection during Encounter 6. \apj, 925(2), 212.
• Giacalone, J., Fahr, H., Fichtner, H., Florinski, V., Heber, B., Hill, M., K{\'ota}, J., Leske, R., Potgieter, M., & Rankin, J. (2022). Anomalous Cosmic Rays and Heliospheric Energetic Particles. \ssr, 218(4), 22.
• Gkioulidou, M., Opher, M., Kornbleuth, M., Dialynas, K., Giacalone, J., Richardson, J., Zank, G., Fuselier, S., Mitchell, D., Krimigis, S., Roussos, E., & Baliukin, I. (2022). On the Energization of Pickup Ions Downstream of the Heliospheric Termination Shock by Comparing 0.52-55 keV Observed Energetic Neutral Atom Spectra to Ones Inferred from Proton Hybrid Simulations. \apjl, 931(2), L21.
• Guo, F., Antiochos, S., Cassak, P., Chen, B., Chen, X., Dong, C., Downs, C., Giacalone, J., Haggerty, C. C., Ji, H., Karpen, J., Klimchuk, J., Li, W., Li, X., Oka, M., Reeves, K. K., Swisdak, M., & Tu, W. (2022). Advancing Theory and Modeling Efforts in Heliophysics. arXiv e-prints, arXiv:2209.03611.
• Guo, F., Zhao, L., Cohen, C. M., Giacalone, J., Leske, R., Wiedenbeck, M., Kahler, S., Li, X., Zhang, Q., Ho, G. C., & Desai, M. I. (2022). Variable Ion Compositions of Solar Energetic Particle Events in the Inner Heliosphere: A Field Line Braiding Model with Compound Injections. \apj, 924(1), 22.
• Kong, X., Chen, B., Guo, F., Shen, C., Li, X., Ye, J., Zhao, L., Jiang, Z., Yu, S., Chen, Y., & Giacalone, J. (2022). Numerical Modeling of Energetic Electron Acceleration, Transport, and Emission in Solar Flares: Connecting Loop-top and Footpoint Hard X-Ray Sources. \apjl, 941(2), L22.
• Kong, X., Ye, J., Chen, B., Guo, F., Shen, C., Li, X., Yu, S., Chen, Y., & Giacalone, J. (2022). A Model of Double Coronal Hard X-Ray Sources in Solar Flares. \apj, 933(1), 93.
• Moradi, A., & Giacalone, J. (2022). The Effect of the Fluctuating Interplanetary Magnetic Field on the Cosmic Ray Intensity Profile of the Ground-level Enhancement (GLE) Events. \apj, 932(1), 73.
• Nikoukar, R., Hill, M. E., Brown, L., Kota, J., Decker, R. B., Dialynas, K., Hamilton, D. C., Krimigis, S. M., Lasley, S., Roelof, E. C., Mitchell, J. G., Florinski, V., Giacalone, J., Richardson, J., & Opher, M. (2022). On the Energy Dependence of Galactic Cosmic Ray Anisotropies in the Very Local Interstellar Medium. \apj, 934(1), 41.
• Perri, S., Bykov, A., Fahr, H., Fichtner, H., & Giacalone, J. (2022). Recent Developments in Particle Acceleration at Shocks: Theory and Observations. \ssr, 218(4), 26.
• Yu, F., Kong, X., Guo, F., Liu, W., Jiang, Z., Chen, Y., & Giacalone, J. (2022). Double-power-law Feature of Energetic Particles Accelerated at Coronal Shocks. \apjl, 925(2), L13.
• Zank, G., Sterken, V., Giacalone, J., M{\"obius}, E., Steiger, R., Stone, E., Krimigis, S., Richardson, J., Linsky, J., Izmodenov, V., & Heber, B. (2022). The Early History of Heliospheric Science and the Spacecraft That Made It Possible. \ssr, 218(4), 34.
• Bandyopadhyay, R., Matthaeus, W., McComas, D., Joyce, C., Szalay, J., Christian, E., Giacalone, J., Schwadron, N., Mitchell, D., Hill, M., McNutt, R., Desai, M., Bale, S., Bonnell, J., Wit, T., Goetz, K., Harvey, P., MacDowall, R., Malaspina, D., , Pulupa, M., et al. (2021). Energetic particle behavior in near-Sun magnetic field switchbacks from PSP. \aap, 650, L4.
• Chhiber, R., Matthaeus, W., Cohen, C., Ruffolo, D., Sonsrettee, W., Tooprakai, P., Seripienlert, A., Chuychai, P., Usmanov, A., Goldstein, M., McComas, D., Leske, R., Szalay, J., Joyce, C., Cummings, A., Roelof, E., Christian, E., Mewaldt, R., Labrador, A., , Giacalone, J., et al. (2021). Magnetic field line random walk and solar energetic particle path lengths. Stochastic theory and PSP/IS\ensuremath{\odot}IS observations. \aap, 650, A26.
• Cohen, C., Christian, E., Cummings, A., Davis, A., Desai, M., Nolfo, G., Giacalone, J., Hill, M., Joyce, C., Labrador, A., Leske, R., Matthaeus, W., McComas, D., McNutt, R., Mewaldt, R., Mitchell, D., Mitchell, J., Rankin, J., Roelof, E., , Schwadron, N., et al. (2021). PSP/IS\ensuremath{\odot}IS observations of the 29 November 2020 solar energetic particle event. \aap, 656, A29.
• Cohen, C., Christian, E., Cummings, A., Davis, A., Desai, M., Nolfo, G., Giacalone, J., Hill, M., Joyce, C., Labrador, A., Leske, R., Matthaeus, W., McComas, D., McNutt, R., Mewaldt, R., Mitchell, D., Mitchell, J., Rankin, J., Roelof, E., , Schwadron, N., et al. (2021). Parker Solar Probe observations of He/H abundance variations in SEP events inside 0.5 au. \aap, 650, A23.
• David, L., Fraschetti, F., Giacalone, J., Wimmer-Schweingruber, R., Berger, L., & Lario, D. (2021). Energy Balance at Interplanetary Shocks: In-situ Measurement of the Fraction in Supra-thermal and Energetic Particles with ACE and Wind. arXiv e-prints, arXiv:2108.07350.
• Desai, M., Mitchell, D., McComas, D., Drake, J., Phan, T., Szalay, J., Roelof, E., Giacalone, J., Hill, M., Christian, E., Schwadron, N., McNutt Jr., ., Wiedenbeck, M., Joyce, C., Cohen, C., Davis, A., Krimigis, S., Leske, R., Matthaeus, W., , Malandraki, O., et al. (2021). Suprathermal Ion Energy spectra and Anisotropies near the Heliospheric Current Sheet crossing observed by the Parker Solar Probe during Encounter 7. arXiv e-prints, arXiv:2111.00954.
• Esman, T., Espley, J., Gruesbeck, J., Klein, K., & Giacalone, J. (2021). Plasma Waves in the Distant Martian Environment: Implications for Mars' Sphere of Influence. Journal of Geophysical Research (Space Physics), 126(11), e29686.
• Getachew, T., McComas, D., Joyce, C., Palmerio, E., Christian, E., Cohen, C., Desai, M., Giacalone, J., Hill, M., Matthaeus, W., McNutt, R., Mitchell, D., Mitchell, J., Rankin, J., Roelof, E., Schwadron, N., Szalay, J., Zank, G., Zhao, L. -., , Lynch, B., et al. (2021). PSP/IS$\odot$IS Observation of a Solar Energetic Particle Event Associated With a Streamer Blowout Coronal Mass Ejection During Encounter 6. arXiv e-prints, arXiv:2112.04671.
• Giacalone, J. (2021). The Transport Equation for the Dispersal of Passive Tracers in a Nonuniform Turbulent Fluid: Numerical Simulations. \apj, 912(2), 83.
• Giacalone, J., Burgess, D., Bale, S., Desai, M., Mitchell, J., Lario, D., Chen, C., Christian, E., Nolfo, G., Hill, M., Matthaeus, W., McComas, D., McNutt, R., Mitchell, D., Roelof, E., Schwadron, N., Getachew, T., & Joyce, C. (2021). Energetic Particles Associated with a Coronal Mass Ejection Shock Interacting with a Convected Magnetic Structure. \apj, 921(2), 102.
• Giacalone, J., Nakanotani, M., Zank, G., K{\`ota}, J., Opher, M., & Richardson, J. (2021). Hybrid Simulations of Interstellar Pickup Protons Accelerated at the Solar-wind Termination Shock at Multiple Locations. \apj, 911(1), 27.
• Guo, F., Giacalone, J., & Zhao, L. (2021). Shock Propagation and Associated Particle Acceleration in the Presence of Ambient Solar-Wind Turbulence. Frontiers in Astronomy and Space Sciences, 8, 27.
• Joyce, C., McComas, D., Schwadron, N., Christian, E., Wiedenbeck, M., McNutt, R., Cohen, C., Leske, R., Mewaldt, R., Stone, E., Labrador, A., Davis, A., Cummings, A., Mitchell, D., Hill, M., Roelof, E., Allen, R., Szalay, J., Rankin, J., , Desai, M., et al. (2021). Time evolution of stream interaction region energetic particle spectra in the inner heliosphere. \aap, 650, L5.
• Joyce, C., McComas, D., Schwadron, N., Vourlidas, A., Christian, E., McNutt, R., Cohen, C., Leske, R., Mewaldt, R., Stone, E., Mitchell, D., Hill, M., Roelof, E., Allen, R., Szalay, J., Rankin, J., Desai, M., Giacalone, J., Matthaeus, W., , Niehof, J., et al. (2021). Energetic particle evolution during coronal mass ejection passage from 0.3 to 1 AU. \aap, 651, A2.
• Lario, D., Richardson, I., Palmerio, E., Lugaz, N., Bale, S., Stevens, M., Cohen, C., Giacalone, J., Mitchell, D., Szabo, A., Nieves-Chinchilla, T. .., Wilson, L., Christian, E., Hill, M., McComas, D., McNutt, R., Schwadron, N., & Wiedenbeck, M. (2021). Comparative Analysis of the 2020 November 29 Solar Energetic Particle Event Observed by Parker Solar Probe. \apj, 920(2), 123.
• Mason, G., Cohen, C., Ho, G., Mitchell, D., Allen, R., Hill, M., Andrews, G., Berger, L., Boden, S., B{\"ottcher}, S., Cernuda, I., Christian, E., Cummings, A., Davis, A., Desai, M., Nolfo, G., Eldrum, S., Elftmann, R., Kollhoff, A., , Giacalone, J., et al. (2021). Solar energetic particle heavy ion properties in the widespread event of 2020 November 29. \aap, 656, L12.
• Mitchell, J., De, N. G., Hill, M., Christian, E., Richardson, I., McComas, D., McNutt, R., Mitchell, D., Schwadron, N., Bale, S., Giacalone, J., Joyce, C., Niehof, J., & Szalay, J. (2021). Energetic Electron Observations by Parker Solar Probe/IS\ensuremath{\odot}IS during the First Widespread SEP Event of Solar Cycle 25 on 2020 November 29. \apj, 919(2), 119.
• Opher, M., Drake, J., Zank, G., Powell, E., Shelley, W., Kornbleuth, M., Florinski, V., Izmodenov, V., Giacalone, J., Fuselier, S., Dialynas, K., Loeb, A., & Richardson, J. (2021). A Turbulent Heliosheath Driven by the Rayleigh-Taylor Instability. \apj, 922(2), 181.
• Pecora, F., Servidio, S., Greco, A., Matthaeus, W., McComas, D., Giacalone, J., Joyce, C., Getachew, T., Cohen, C., Leske, R., Wiedenbeck, M., McNutt, R., Hill, M., Mitchell, D., Christian, E., Roelof, E., Schwadron, N., & Bale, S. (2021). Parker Solar Probe observations of helical structures as boundaries for energetic particles. \mnras, 508(2), 2114-2122.
• Richardson, J., Cummings, A., Burlaga, L., Giacalone, J., Opher, M., & Stone, E. (2021). Using Magnetic Flux Conservation to Determine Heliosheath Speeds. \apjl, 919(2), L28.
• Schwadron, N., Joyce, C., Aly, A., Cohen, C., Desai, M., McComas, D., Niehof, J., M{\"obius}, E., Lee, M., Bower, J., Bale, S., Case, A., Christian, E., Davis, A., Wet, W., Goetz, K., Giacalone, J., Hill, M., Allen, R., , Kasper, J., et al. (2021). A new view of energetic particles from stream interaction regions observed by Parker Solar Probe. \aap, 650, A24.
• Bandyopadhyay, R., Matthaeus, W., Parashar, T., Chhiber, R., Ruffolo, D., Goldstein, M., Maruca, B., Chasapis, A., Qudsi, R., McComas, D., Christian, E., Szalay, J., Joyce, C., Giacalone, J., Schwadron, N., Mitchell, D., Hill, M., Wiedenbeck, M., McNutt Jr., ., , Desai, M., et al. (2020). Observations of Energetic-particle Population Enhancements along Intermittent Structures near the Sun from the Parker Solar Probe. \apjs, 246(2), 61.
• Chhiber, R., Matthaeus, W., Cohen, C., Ruffolo, D., Sonsrettee, W., Tooprakai, P., Seripienlert, A., Chuychai, P., Usmanov, A., Goldstein, M., McComas, D., Leske, R., Christian, E., Mewaldt, R., Labrador, A., Szalay, J., Joyce, C., Giacalone, J., Schwadron, N., , Mitchell, D., et al. (2020). Magnetic Field Line Random Walk and Solar Energetic Particle Path Lengths: Stochastic Theory and PSP/ISoIS Observation. arXiv e-prints, arXiv:2011.08329.
• Cohen, C., Christian, E., Cummings, A., Davis, A., Desai, M., Giacalone, J., Hill, M., Joyce, C., Labrador, A., Leske, R., Matthaeus, W., McComas, D., McNutt Jr., ., Mewaldt, R., Mitchell, D., Rankin, J., Roelof, E., Schwadron, N., Stone, E., , Szalay, J., et al. (2020). Energetic Particle Increases Associated with Stream Interaction Regions. \apjs, 246(2), 20.
• Dalla, S., Nolfo, G., Bruno, A., Giacalone, J., Laitinen, T., Thomas, S., Battarbee, M., & Marsh, M. (2020). 3D propagation of relativistic solar protons through interplanetary space. \aap, 639, A105.
• Desai, M., Mitchell, D., Szalay, J., Roelof, E., Giacalone, J., Hill, M., McComas, D., Christian, E., Schwadron, N., McNutt Jr., ., Wiedenbeck, M., Joyce, C., Cohen, C., Ebert, R., Dayeh, M., Allen, R., Davis, A., Krimigis, S., Leske, R., , Matthaeus, W., et al. (2020). Properties of Suprathermal-through-energetic He Ions Associated with Stream Interaction Regions Observed over the Parker Solar Probe's First Two Orbits. \apjs, 246(2), 56.
• Fraschetti, F., & Giacalone, J. (2020). Bi-directional streaming of particles accelerated at the STEREO-A shock on 2008 March 9. \mnras, 499(2), 2087-2093.
• Giacalone, J. (2020). Erratum: ``The Acceleration of Charged Particles at a Spherical Shock Moving through an Irregular Magnetic Field'' (2017, ApJ, 848, 123). \apj, 898(1), 93.
• Giacalone, J., & Jokipii, J. (2020). Erratum: ``A New Model for the Heliosphere's 'IBEX Ribbon''' (2017, ApJL, 812, L9). \apjl, 897(2), L45.
• Giacalone, J., Mitchell, D., Allen, R., Hill, M., McNutt Jr., ., Szalay, J., Desai, M., Rouillard, A., Kouloumvakos, A., McComas, D., Christian, E., Schwadron, N., Wiedenbeck, M., Bale, S., Brown, L., Case, A., Chen, X., Cohen, C., Joyce, C., , Kasper, J., et al. (2020). Solar Energetic Particles Produced by a Slow Coronal Mass Ejection at \ensuremath{\sim}0.25 au. \apjs, 246(2), 29.
• Hill, M., Mitchell, D., Allen, R., Nolfo, G., Vourlidas, A., Brown, L., Jones, S., McComas, D., McNutt Jr., ., Mitchell, J., Szalay, J., Wallace, S., Arge, C., Christian, E., Cohen, C., Crew, A., Desai, M., Giacalone, J., Henney, C., , Joyce, C., et al. (2020). Small, Low-energy, Dispersive Solar Energetic Particle Events Observed by Parker Solar Probe. \apjs, 246(2), 65.
• Horbury, T., O'Brien, H., Carrasco Blazquez, I., Bendyk, M., Brown, P., Hudson, R., Evans, V., Oddy, T., Carr, C., Beek, T., Cupido, E., Bhattacharya, S., Dominguez, J. -., Matthews, L., Myklebust, V., Whiteside, B., Bale, S., Baumjohann, W., Burgess, D., , Carbone, V., et al. (2020). The Solar Orbiter magnetometer. \aap, 642, A9.
• Joyce, C., McComas, D., Christian, E., Schwadron, N., Wiedenbeck, M., McNutt Jr., ., Cohen, C., Leske, R., Mewaldt, R., Stone, E., Labrador, A., Davis, A., Cummings, A., Mitchell, D., Hill, M., Roelof, E., Szalay, J., Rankin, J., Desai, M., , Giacalone, J., et al. (2020). Energetic Particle Observations from the Parker Solar Probe Using Combined Energy Spectra from the IS\ensuremath{\odot}IS Instrument Suite. \apjs, 246(2), 41.
• Kong, X., Guo, F., Shen, C., Chen, B., Chen, Y., & Giacalone, J. (2020). Dynamical Modulation of Solar Flare Electron Acceleration due to Plasmoid-shock Interactions in the Looptop Region. \apjl, 905(2), L16.
• Leske, R., Christian, E., Cohen, C., Cummings, A., Davis, A., Desai, M., Giacalone, J., Hill, M., Joyce, C., Krimigis, S., Labrador, A., Malandraki, O., Matthaeus, W., McComas, D., McNutt Jr., ., Mewaldt, R., Mitchell, D., Posner, A., Rankin, J., , Roelof, E., et al. (2020). Observations of the 2019 April 4 Solar Energetic Particle Event at the Parker Solar Probe. \apjs, 246(2), 35.
• Mitchell, D., Giacalone, J., Allen, R., Hill, M., McNutt, R., McComas, D., Szalay, J., Schwadron, N., Rouillard, A., Bale, S., Chaston, C., Pulupa, M., Whittlesey, P., Kasper, J., MacDowall, R., Christian, E., Wiedenbeck, M., & Matthaeus, W. (2020). CME-associated Energetic Ions at 0.23 au: Consideration of the Auroral Pressure Cooker Mechanism Operating in the Low Corona as a Possible Energization Process. \apjs, 246(2), 59.
• Nakanotani, M., Zank, G., Adhikari, L., Zhao, L. -., Giacalone, J., Opher, M., & Richardson, J. (2020). The Downwind Solar Wind: Model Comparison with Pioneer 10 Observations. \apjl, 901(2), L23.
• Nieves-Chinchilla, T., Szabo, A., Korreck, K. E., Alzate, N., Balmaceda, L. A., Lavraud, B., Paulson, K., Narock, A. A., Wallace, S., Jian, L. K., Luhmann, J. G., Morgan, H., Higginson, A., Arge, C. N., Bale, S. D., Case, A. W., Wit, T., Giacalone, J., Goetz, K., , Harvey, P. R., et al. (2020). Analysis of the Internal Structure of the Streamer Blowout Observed by the Parker Solar Probe During the First Solar Encounter. \apjs, 246(2), 63.
• Schwadron, N., Bale, S., Bonnell, J., Case, A., Christian, E., Cohen, C., Cummings, A., Davis, A., Wit, T., Wet, W., Desai, M., Joyce, C., Goetz, K., Giacalone, J., Gorby, M., Harvey, P., Heber, B., Hill, M., Karavolos, M., , Kasper, J., et al. (2020). Seed Population Preconditioning and Acceleration Observed by the Parker Solar Probe. \apjs, 246(2), 33.
• Wiedenbeck, M., Bu{\v{c}\'\ik}, R., Mason, G., Ho, G., Leske, R., Cohen, C., Christian, E., Cummings, A., Davis, A., Desai, M., Giacalone, J., Haggerty, D., Hill, M., Joyce, C., Labrador, A., Malandraki, O., Matthaeus, W., McComas, D., McNutt Jr., ., , Mewaldt, R., et al. (2020). $^3$He-rich Solar Energetic Particle Observations at the Parker Solar Probe and near Earth. \apjs, 246(2), 42.
• Zirnstein, E., Giacalone, J., Kumar, R., McComas, D., Dayeh, M., & Heerikhuisen, J. (2020). Turbulence in the Local Interstellar Medium and the IBEX Ribbon. \apj, 888(1), 29.
• Esman, T., Espley, J., Gruesbeck, J., & Giacalone, J. (2019). ELF Waves in the Martian Ionosphere: Lightning, Field Line Resonances, and Instabilities?. LPI Contributions, 2089, 6041.
• Kong, X., Guo, F., Chen, Y., & Giacalone, J. (2019). The Acceleration of Energetic Particles at Coronal Shocks and Emergence of a Double Power-law Feature in Particle Energy Spectra. \apj, 883(1), 49.
• Kong, X., Guo, F., Shen, C., Chen, B., Chen, Y., Musset, S., Glesener, L., Pongkitiwanichakul, P., & Giacalone, J. (2019). The Acceleration and Confinement of Energetic Electrons by a Termination Shock in a Magnetic Trap: An Explanation for Nonthermal Loop-top Sources during Solar Flares. \apjl, 887(2), L37.
• Lario, D., Berger, L., Decker, R., Wimmer-Schweingruber, R., Wilson, I., Giacalone, J., & Roelof, E. (2019). Evolution of the Suprathermal Proton Population at Interplanetary Shocks. \aj, 158(1), 12.
• Nolfo, G., Bruno, A., Ryan, J., Dalla, S., Giacalone, J., Richardson, I., Christian, E., Stochaj, S., Bazilevskaya, G., Boezio, M., Martucci, M., Mikhailov, V., & Munini, R. (2019). Comparing Long-duration Gamma-Ray Flares and High-energy Solar Energetic Particles. \apj, 879(2), 90.
• Wang, X., Giacalone, J., Yan, Y., Ding, M., Li, C., Lu, H., & Shan, H. (2019). Particle Acceleration at the Pileup Collision of the Twin Shock. \apj, 885(1), 66.
• Fraschetti, F., Katsuda, S., Sato, T., Jokipii, J., & Giacalone, J. (2018). Vortical Amplification of the Magnetic Field at an Inward Shock of Supernova Remnant Cassiopeia A. Physical Review Letters, 120(25), 251101.
• McComas, D., Christian, E., Schwadron, N., Fox, N., Westlake, J., Allegrini, F., Baker, D., Biesecker, D., Bzowski, M., Clark, G., Cohen, C., Cohen, I., Dayeh, M., Decker, R., Nolfo, G., Desai, M., Ebert, R., Elliott, H., Fahr, H., , Frisch, P., et al. (2018). Interstellar Mapping and Acceleration Probe (IMAP): A New NASA Mission. \ssr, 214, 116.
• Giacalone, J. (2017). The Acceleration of Charged Particles at a Spherical Shock Moving through an Irregular Magnetic Field. \apj, 848, 123.
• Kong, X., Guo, F., Giacalone, J., Li, H., & Chen, Y. (2017). The Acceleration of High-energy Protons at Coronal Shocks: The Effect of Large-scale Streamer-like Magnetic Field Structures. \apj, 851, 38.
• Wang, X., Giacalone, J., Yan, Y., Ding, M., Wang, N., & Shan, H. (2017). Particle Acceleration in Two Converging Shocks. \apj, 842, 74.
• {Desai}, M., , J. (2016). Large gradual solar energetic particle events. Living Reviews in Solar Physics, 13, 3.
• {McComas}, D., {Alexander}, N., {Angold}, N., {Bale}, S., {Beebe}, C., {Birdwell}, B., {Boyle}, M., {Burgum}, J., {Burnham}, J., {Christian}, E., {Cook}, W., {Cooper}, S., {Cummings}, A., {Davis}, A., {Desai}, M., {Dickinson}, J., {Dirks}, G., {Do}, D., {Fox}, N., , {Giacalone}, J., et al. (2016). Integrated Science Investigation of the Sun (ISIS): Design of the Energetic Particle Investigation. \ssr, 204, 187-256.
• {Riley}, P., {Caplan}, R., {Giacalone}, J., {Lario}, D., , Y. (2016). Properties of the Fast Forward Shock Driven by the July 23 2012 Extreme Coronal Mass Ejection. \apj, 819, 57.
• {Sun}, P., {Jokipii}, J., , J. (2016). Pitch-angle Scattering of Energetic Charged Particles in Nearly Constant Magnitude Magnetic Turbulence. \apj, 827, 16.
• Giacalone, J., & Jokipii, J. R. (2015). A NEW MODEL FOR THE HELIOSPHERE'S "IBEX RIBBON". ASTROPHYSICAL JOURNAL LETTERS, 812(1).
• {Fraschetti}, F., , J. (2015). "{Localized enhancements of energetic particles at oblique collisionless shocks}". mnras, 448, 3555-3566.
• {Giacalone}, J. (2015). "{Diffusive Shock Acceleration of High-energy Charged Particles at Fast Interplanetary Shocks: A Parameter Survey}". apj, 799, 80.
• {Giacalone}, J., , L. (2015). "{Hybrid simulation of the interaction of solar wind protons with a concentrated lunar magnetic anomaly}". Journal of Geophysical Research (Space Physics), 120, 4081-4094.
• {Guo}, F., , J. (2015). "{The Acceleration of Electrons at Collisionless Shocks Moving Through a Turbulent Magnetic Field}". apj, 802, 97.
• {Jokipii}, J., {K{'o}ta}, J., , J. (2015). "{Effects of Large-Scale Simple Velocity Shear on a Fluctuating Interplanetary Magnetic Field}". Journal of Physics Conference Series, 577, 012015.
• {Neugebauer}, M., , J. (2015). "{Energetic particles, tangential discontinuities, and solar flux tubes}". Journal of Geophysical Research (Space Physics), 120, 8281-8287.
• {Riley}, P., {Caplan}, R., {Giacalone}, J., {Lario}, D., , Y. (2015). "{Properties of the Fast Forward Shock Driven by the July 23 2012 Extreme Coronal Mass Ejection}". ArXiv e-prints.
• {Riley}, P., {Giacalone}, J., , Y. (2015). "{Properties of the Fast Forward Shock Driven by the July 23 2012 Extreme Coronal Mass Ejection}". IAU General Assembly, 22, 2255759.
• {Schwadron}, N., {Lee}, M., {Gorby}, M., {Lugaz}, N., {Spence}, H., {Desai}, M., {T{"o}r{"o}k}, T., {Downs}, C., {Linker}, J., {Lionello}, R., {Miki{'c}}, Z., {Riley}, P., {Giacalone}, J., {Jokipii}, J., {Kota}, J., , K. (2015). "{Broken Power-law Distributions from Low Coronal Compression Regions or Shocks}". Journal of Physics Conference Series, 642, 012025.
• {Schwadron}, N., {Lee}, M., {Gorby}, M., {Lugaz}, N., {Spence}, H., {Desai}, M., {T{"o}r{"o}k}, T., {Downs}, C., {Linker}, J., {Lionello}, R., {Miki{'c}}, Z., {Riley}, P., {Giacalone}, J., {Jokipii}, J., {Kota}, J., , K. (2015). "{Particle Acceleration at Low Coronal Compression Regions and Shocks}". apj, 810, 97.
• {Tessein}, J., {Ruffolo}, D., {Matthaeus}, W., {Wan}, M., {Giacalone}, J., , M. (2015). "{Effect of Coherent Structures on Energetic Particle Intensity in the Solar Wind at 1 AU}". apj, 812, 68.
• {Wang}, X., {Giacalone}, J., {Yan}, Y., {Ding}, M., {Wang}, N., , H. (2015). "{Particles Acceleration in Converged Two Shocks}". ArXiv e-prints.
• Guo, F., & Giacalone, J. (2014). Small-scale gradients of charged particles in the heliospheric magnetic field. Astrophysical Journal, 780(1).
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  Abstract: Using numerical simulations of charged-particles propagating in the heliospheric magnetic field, we study small-scale gradients, or "dropouts," in the intensity of solar energetic particles seen at 1 AU. We use two turbulence models, the foot-point random motion model and the two-component model, to generate fluctuating magnetic fields similar to spacecraft observations at 1 AU. The turbulence models include a Kolmogorov-like magnetic field power spectrum containing a broad range of spatial scales from those that lead to large-scale field-line random walk to small scales leading to resonant pitch-angle scattering of energetic particles. We release energetic protons (20 keV-10 MeV) from a spatially compact and instantaneous source. The trajectories of energetic charged particles in turbulent magnetic fields are numerically integrated. Spacecraft observations are mimicked by collecting particles in small windows when they pass the windows at a distance of 1 AU. We show that small-scale gradients in the intensity of energetic particles and velocity dispersions observed by spacecraft can be reproduced using the foot-point random motion model. However, no dropouts are seen in simulations using the two-component magnetic turbulence model. We also show that particle scattering in the solar wind magnetic field needs to be infrequent for intensity dropouts to form. © 2014. The American Astronomical Society. All rights reserved..
• {Giacalone}, J. (2014). "{The acceleration of charged particles from thermal to suprathermal energies at strong shocks in the solar wind}". AGU Fall Meeting Abstracts.
• {Jokipii}, J., , J. (2014). "{A Heliosphere Buffeted by Interstellar Turbulence?}". AGU Fall Meeting Abstracts.
• {Schwadron}, N., {Gorby}, M., {T{"o}r{"o}k}, T., {Downs}, C., {Linker}, J., {Lionello}, R., {Miki{'c}}, Z., {Riley}, P., {Giacalone}, J., {Chandran}, B., {Germaschewski}, K., {Isenberg}, P., {Lee}, M., {Lugaz}, N., {Smith}, S., {Spence}, H., {Desai}, M., {Kasper}, J., {Kozarev}, K., , {Korreck}, K., et al. (2014). "{Synthesis of 3-D Coronal-Solar Wind Energetic Particle Acceleration Modules}". Space Weather, 12, 323-328.
• {Tessein}, J., {Ruffolo}, D., {Wan}, M., {Matthaeus}, W., {Neugebauer}, M., , J. (2014). "{Effect of Coherent Structures on Energetic Particle Intensity in the Solar Wind at 1 AU}". AGU Fall Meeting Abstracts.
• Giacalone, J. (2013). Cosmic-ray transport and interaction with shocks. Space Science Reviews, 176(1-4), 73-88.
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  Abstract: This paper reviews selected topics in cosmic-ray transport in the heliosphere, as well as recent insights on the interaction of cosmic rays with shocks. Topics include: (a) recent observations suggesting very long inferred scattering mean-free paths of cosmic rays, (b) recent insights into the diffusion of cosmic rays normal to a magnetic field, (c) the physics of super-diffusion and sub-diffusion, and (e) the interaction of cosmic rays with shocks moving through large-scale irregular magnetic fields. © 2011 Springer Science+Business Media B.V.
• Guo, F., & Giacalone, J. (2013). The acceleration of thermal protons at parallel collisionless shocks: Three-dimensional hybrid simulations. Astrophysical Journal, 773(2).
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  Abstract: We present three-dimensional hybrid simulations of collisionless shocks that propagate parallel to the background magnetic field to study the acceleration of protons that forms a high-energy tail on the distribution. We focus on the initial acceleration of thermal protons and compare it with results from one-dimensional simulations. We find that for both one- and three-dimensional simulations, particles that end up in the high-energy tail of the distribution later in the simulation gained their initial energy right at the shock. This confirms previous results but is the first to demonstrate this using fully three-dimensional fields. The result is not consistent with the "thermal leakage" model. We also show that the gyrocenters of protons in the three-dimensional simulation can drift away from the magnetic field lines on which they started due to the removal of ignorable coordinates that exist in one- and two-dimensional simulations. Our study clarifies the injection problem for diffusive shock acceleration. © 2013. The American Astronomical Society. All rights reserved.
• Tessein, J. A., Matthaeus, W. H., Wan, M., Osman, K. T., Ruffolo, D., & Giacalone, J. (2013). Association of suprathermal particles with coherent structures and shocks. Astrophysical Journal Letters, 776(1).
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  Abstract: Various mechanisms have been proposed to explain observed suprathermal particle populations in the solar wind, including direct acceleration at flares, stochastic acceleration, shock acceleration, and acceleration by random compression or reconnection sites. Using magnetic field and suprathermal particle data from the Advanced Composition Explorer (ACE), we identify coherent structures and interplanetary shocks, and analyze the temporal association of energetic particle fluxes with these coherent structures. Coherent structures having a range of intensities are identified using the magnetic Partial Variance of Increments statistic, essentially a normalized vector increment. A stronger association of energetic particle flux in the 0.047-4.75 MeV range is found with intense magnetic discontinuities than is found with shocks. Nevertheless, the average profile of suprathermals near shocks is quite consistent with standard models of diffusive shock acceleration, while a significant amount of the energetic particles measured and strong discontinuities are found by ACE within six hours of a shock. This evidence supports the view that multiple mechanisms contribute to the acceleration and transport of interplanetary suprathermal particles. © 2013. The American Astronomical Society. All rights reserved..
• Fraschetti, F., & Giacalone, J. (2012). Early-time velocity autocorrelation for charged particles diffusion and drift in static magnetic turbulence. Astrophysical Journal, 755(2).
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  Abstract: Using test-particle simulations, we investigate the temporal dependence of the two-point velocity correlation function for charged particles scattering in a time-independent spatially fluctuating magnetic field derived from a three-dimensional isotropic turbulence power spectrum. Such a correlation function allowed us to compute the spatial coefficients of diffusion both parallel and perpendicular to the average magnetic field. Our simulations confirm the dependence of the perpendicular diffusion coefficient on turbulence energy density and particle energy predicted previously by a model for early-time charged particle transport. Using the computed diffusion coefficients, we exploit the particle velocity autocorrelation to investigate the timescale over which the particles "decorrelate" from the solution to the unperturbed equation of motion. Decorrelation timescales are evaluated for parallel and perpendicular motions, including the drift of the particles from the local magnetic field line. The regimes of strong and weak magnetic turbulence are compared for various values of the ratio of the particle gyroradius to the correlation length of the magnetic turbulence. Our simulation parameters can be applied to energetic particles in the interplanetary space, cosmic rays at the supernova shocks, and cosmic-rays transport in the intergalactic medium. © 2012. The American Astronomical Society. All rights reserved.
• Giacalone, J. (2012). Energetic charged particles associated with strong interplanetary shocks. Astrophysical Journal, 761(1).
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  Abstract: We analyze observations of energetic charged particles associated with many strong interplanetary shocks seen by Advanced Composition Explorer. We focus primarily on 47-187 keV suprathermal protons and restrict our analysis to strong interplanetary shocks (Alfvén Mach number >3 and the shock density compression >2.5). Eighteen shocks meeting this criterion from 1998 to 2003 were analyzed. All 18 had enhancements of the 47-65 keV proton intensity above the intensity seen one day before the shock. In 17 events, the particle intensity either rose to a quasi-plateau or peaked within 10 minutes of the shock. Most had intensities at the shock exceeding 100 times more than that seen the day before the shock arrived. The time-intensity profiles of the energetic proton events in many cases reveal a rise before the shock passage reaching a quasi-plateau or local peak at the shock, followed by a gradual decline. This suggests that the shock itself is the source of energetic particles. Energy spectra behind the shock were fit to an assumed power law over the interval from 46 to 187 keV, and the resulting spectral index was compared to the plasma density jump across each shock. Most events agree with the prediction of diffusive shock acceleration theory to within the observational uncertainties. We also analyzed a few selected events to determine the particle spatial diffusion coefficients and acceleration timescales. We find that the time to accelerate protons to 50 keV is of the order of an hour. © 2012. The American Astronomical Society. All rights reserved..
• Giacalone, J., & Jokipii, J. R. (2012). Suprathermal ions associated with strong interplanetary shocks. AIP Conference Proceedings, 1436, 130-135.
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  Abstract: We analyze ACE observations of 47-66 keV ions for many strong interplanetary shocks seen from 1998-2003. We find that for nearly all-27 out of 30-of the strong shocks we analyzed, suprathermal ions were seen to be enhanced at the time of the shock passage. We find that many of the observed time-intensity profiles are consistent with predictions from the theory of diffusive shock acceleration. Our results suggest that shocks are efficient accelerators of suprathermal ions. © 2012 American Institute of Physics.
• Giacalone, J., & Jokipii, J. R. (2012). The longitudinal transport of energetic ions from impulsive solar flares in interplanetary space. Astrophysical Journal Letters, 751(2).
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  Abstract: We present a study of the longitudinal spread of energetic charged particles from a localized instantaneous compact source on the Sun. Our study utilizes a diffusive-transport model for the propagation of energetic ions in interplanetary space. We show that even for very small values of the ratio of perpendicular to parallel diffusion coefficients - a few percent - the particles spread significantly in longitude. Spatial diffusion and adiabatic energy loss of ions in the interplanetary plasma cause impulsive particle events at Earth's orbit to last a few days. In this time, the combination of transport both along and across the local Parker-spiral magnetic field and the longitudinal motion of the magnetic lines of forces rooted at the Sun as it rotates leads to substantial longitudinal transport of the particles. We show that spacecraft separated by as much as 180° or more may observe events associated with compact solar sources, such as those from impulsive solar flares. Our results are qualitatively consistent with recent multi-spacecraft observations. © 2012. The American Astronomical Society. All rights reserved..
• Giacalone, J., Drake, J. F., & Jokipii, J. R. (2012). The acceleration mechanism of anomalous cosmic rays. Space Science Reviews, 173(1-4), 283-307.
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  Abstract: This paper reviews our current understanding of the acceleration mechanism of anomalous cosmic rays (ACRs). ACRs were first discovered in the early 1970s and soon afterwards it was recognized that they were accelerated interstellar pickup ions that obtained most of their energization in the outer heliosphere. Their observed composition and charge state suggest they are accelerated to over 200 MeV total energy in about a year. Diffusive shock acceleration at the solar-wind termination shock, which provided a natural explanation for spacecraft observations prior to the Voyager crossings of the termination shock in 2004 and 2007, was the long-held paradigm for the acceleration mechanism. But when both Voyagers crossed the shock, the ACR energy spectrum remained modulated, suggesting a source more distant than the shock. While shock acceleration remains a popular mechanism, other ideas have emerged recently to explain the observations. This review focuses on three main acceleration mechanisms that have been proposed: (a) acceleration at the termination shock including new effects such as the global blunt-shape of the shock and large-scale turbulence, (b) acceleration by magnetic reconnection in the heliosheath, and (c) acceleration by diffusive compression acceleration in the heliosheath. © 2012 Springer Science+Business Media B.V.
• Guo, F., & Giacalone, J. (2012). Particle acceleration at a flare termination shock: Effect of large-scale magnetic turbulence. Astrophysical Journal, 753(1).
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  Abstract: We investigate the acceleration of charged particles (both electrons and protons) at collisionless shocks predicted to exist in the vicinity of solar flares. The existence of standing termination shocks has been examined by flare models and numerical simulations. We study electron energization by numerically integrating the equations of motion of a large number of test-particle electrons in the time-dependent two-dimensional electric and magnetic fields generated from hybrid simulations (kinetic ions and fluid electron) using parameters typical of the solar flare plasma environment. The shock is produced by injecting plasma flow toward a rigid piston. Large-scale magnetic fluctuations - known to exist in plasmas and known to have important effects on the nonthermal electron acceleration at shocks - are also included in our simulations. For the parameters characteristic of the flaring region, our calculations suggest that the termination shock formed in the reconnection outflow region (above post-flare loops) could accelerate electrons to a kinetic energy of a few MeV within 100 ion cyclotron periods, which is of the order of a millisecond. Given a sufficient turbulence amplitude level (δB 2/B 20 0.3), about 10% of thermal test-particle electrons are accelerated to more than 15keV. We find that protons are also accelerated, but not to as high energy in the available time and the energy spectra are considerably steeper than that of the electrons for the parameters used in our simulations. Our results are qualitatively consistent with the observed hard X-ray emissions in solar flares. © 2012. The American Astronomical Society. All rights reserved.
• Guo, F., & Giacalone, J. (2012). The acceleration of electrons at perpendicular shocks and its implication for solar energetic particle events. AIP Conference Proceedings, 1500(1), 93-99.
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  Abstract: We present a study of the acceleration of electrons at a perpendicular shock that propagates through a turbulentmagnetic field. The energization process of electrons is investigated by utilizing a combination of hybrid (kinetic ions and fluid electron) simulations and test-particle electron simulations. In this method, the motions of the test-particle electrons are numerically integrated in the time-dependent electric and magnetic fields generated by two-dimensional hybrid simulations. We show that large-scale magnetic fluctuations effect electrons in a number of ways and lead to efficient and rapid energization at the shock front. Since the electrons mainly follow along magnetic lines of force, the large-scale braiding of field lines in space allows the fast-moving electrons to interact with the shock front and get accelerated multiple times. Ripples in the shock front occurring at various scales will also contribute to the acceleration by mirroring the electrons. Our calculation shows that this process favors electron acceleration at perpendicular shocks. The acceleration efficiency is critically dependent on the turbulence amplitude and coherence length. We also discuss the implication of this study for solar energetic particles (SEPs) by comparing the acceleration of electrons with that of protons. Their correlation indicates that perpendicular shocks play an important role in SEP events. © 2012 American Institute of Physics.
• Guo, F., Shengtai, L. i., Hui, L. i., Giacalone, J., Jokipii, J. R., & David, L. i. (2012). On the amplification of magnetic field by a supernova blast shock wave in a turbulent medium. Astrophysical Journal, 747(2).
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  Abstract: We have performed extensive two-dimensional magnetohydrodynamic simulations to study the amplification of magnetic fields when a supernova blast wave propagates into a turbulent interstellar plasma. The blast wave is driven by injecting high pressure in the simulation domain. The interstellar magnetic field can be amplified by two different processes, occurring in different regions. One is facilitated by the fluid vorticity generated by the "rippled" shock front interacting with the background turbulence. The resulting turbulent flow keeps amplifying the magnetic field, consistent with earlier work. The other process is facilitated by the growth of the Rayleigh-Taylor instability at the contact discontinuity between the ejecta and the shocked medium. This can efficiently amplify the magnetic field and tends to produce the highest magnetic field. We investigate the dependence of the amplification on numerical parameters such as grid-cell size and on various physical parameters. We show that the magnetic field has a characteristic radial profile such that the downstream magnetic field gets progressively stronger away from the shock. This is because the downstream magnetic field needs a finite time to reach the efficient amplification, and will get further amplified in the Rayleigh-Taylor region. In our simulation, we do not observe a systematic strong magnetic field within a small distance to the shock. This indicates that if the magnetic-field amplification in supernova remnants indeed occurs near the shock front, other processes such as three-dimensional instabilities, plasma kinetics, and/or cosmic ray effect may need to be considered to explain the strong magnetic field in supernova remnants. © 2012 The American Astronomical Society. All rights reserved.
• Lee, M. A., Mewaldt, R. A., & Giacalone, J. (2012). Shock acceleration of ions in the heliosphere. Space Science Reviews, 173(1-4), 247-281.
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  Abstract: Energetic particles constitute an important component of the heliospheric plasma environment. They range from solar energetic particles in the inner heliosphere to the anomalous cosmic rays accelerated at the interface of the heliosphere with the local interstellar medium. Although stochastic acceleration by fluctuating electric fields and processes associated with magnetic reconnection may account for some of the particle populations, the majority are accelerated by the variety of shock waves present in the solar wind. This review focuses on gradual solar energetic particle (SEP) events including their energetic storm particle (ESP) phase, which is observed if and when an associated shock wave passes Earth. Gradual SEP events are the intense long-duration events responsible for most space weather disturbances of Earth's magnetosphere and upper atmosphere. The major characteristics of gradual SEP events are first described including their association with shocks and coronal mass ejections (CMEs), their ion composition, and their energy spectra. In the context of acceleration mechanisms in general, the acceleration mechanism responsible for SEP events, diffusive shock acceleration, is then described in some detail including its predictions for a planar stationary shock, shock modification by the energetic particles, and wave excitation by the accelerating ions. Finally, some complexities of shock acceleration are addressed, which affect the predictive ability of the theory. These include the role of temporal and spatial variations, the distinction between the plasma and wave compression ratios at the shock, the injection of thermal plasma at the shock into the process of shock acceleration, and the nonlinear evolution of ion-excited waves in the vicinity of the shock. © 2012 Springer Science+Business Media B.V.
• Chollet, E. E., & Giacalone, J. (2011). Evidence of confinement of solar-energetic particles to interplanetary magnetic field lines. Astrophysical Journal, 728(1).
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  Abstract: We present new observations of solar-energetic particles (SEPs) associated with impulsive solar flares that show evidence for their confinement to interplanetary magnetic field lines. Some SEP events exhibit intermittent intensity dropouts because magnetic field lines filled with and empty of particle flux mix together. The edges of these dropouts are observed to be very sharp, suggesting that particles cannot easily move from a filled to an empty field line in the time available during their transport from the Sun. In this paper, we perform high time-resolution observations of intensity fall-off at the edges of observed SEP dropouts in order to look for signatures of particle motion off field lines. However, the statistical study is dominated by one particularly intense event. The inferred length scale of the intensity decay is comparable to the gyroradii of the particles, suggesting that particles only rarely scatter off magnetic field lines during interplanetary transport. © 2011. The American Astronomical Society. All rights reserved. Printedin the U.S.A.
• Greenfield, E. J., Jokipii, J. R., & Giacalone, J. (2011). The physics of partially ionized gas with applications to processes in the interstellar medium. AIP Conference Proceedings, 1366, 115-121.
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  Abstract: The dynamical equations for a partially ionized plasma are a matter of some recent controversy. Understanding this problem is important in understanding the interaction of the interstellar medium with the heliosphere and for understanding the spectrum of interstellar turbulence. If collision scales are much smaller than the internal interaction scales such as the ion gyroradius, the fluid approximation may be used. The analysis then must deal with at least three fluids (protons, electrons, and neutrals) which are coupled to each other by collisions and/or electromagnetic fields. Often, the proton and electron gyro-radii are much smaller than the collision length scales, so the electric and magnetic fields dominate the motions of the electrons and protons. In this case, the only important particle-particle collisions are those of the electrons and protons with the neutral atoms. Since the three species have, in general, different velocities, it is not immediately clear which fluid velocity to use. This ambiguity in the choice of fluid velocity has led to recent confusion regarding the physics of partially ionized plasmas. If the neutrals have a significant fraction of the mass, working in the center-of-mass coordinate frame can result in dynamical equations that differ greatly from those of ideal MHD. This is because the magnetic field is not frozen into the frame moving at the center-of-mass velocity, which leads to additional effects on the magnetic field that can be difficult to understand intuitively. To the extent that the electron mass is negligible, the magnetic field is actually found to be frozen into the frame moving with the electron bulk velocity. If we then take U to be the bulk velocity of the proton fluid the resulting dynamical equations closely resemble those of ideal MHD with the exception of the Hall term in the induction equation. Similarly, the frequently used Cowling conductivity also depends on the choice of coordinate frame. These conclusions address directly the recent controversy regarding the interaction of the interstellar medium with the heliosphere and also impact our understanding of interstellar turbulence. © 2011 American Institute of Physics.
• Chollet, E. E., Giacalone, J., & Mewaldt, R. A. (2010). Effects of interplanetary transport on derived energetic particle source strengths. Journal of Geophysical Research A: Space Physics, 115(6).
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  Abstract: We study the transport of solar energetic particles (SEPs) in the inner heliosphere in order to relate observations made by an observer at 1 AU to the number and total energy content of accelerated particles at the source, assumed to be near the Sun. We use a numerical simulation that integrates the trajectories of a large number of individual particles moving in the interplanetary magnetic field. We model pitch angle scattering and adiabatic cooling of energetic ions with energies from 50 keV nucleon-1 to 100 MeV nucleon-1. Among other things, we determine the number of times that particles of a given energy cross 1 AU and the average energy loss that they suffer because of adiabatic deceleration in the solar wind. We use a number of different forms of the interplanetary spatial diffusion coefficient and a wide range of scattering mean-free paths and consider a number of different ion species in order to generate a wide range of simulation results that can be applied to individual SEP events. We apply our simulation results to observations made at 1 AU of the 20 February 2002 solar energetic particle event, finding the original energy content of several species. We find that estimates of the source energy based on SEP measurements at 1 AU are relatively insensitive to the mean-free path and scattering scheme if adiabatic cooling and multiple crossings are taken into account. Copyright © 2010 by the American Geophysical Union.
• Chollet, E., Skoug, R., Steinberg, J., Crooker, N., & Giacalone, J. (2010). Reconnection and disconnection: Observations of suprathermal electron heat flux dropouts. AIP Conference Proceedings, 1216, 600-603.
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  Abstract: Suprathermal electron heat flux dropouts (HFD) serve as a sensitive test of the magnetic topology of the inner heliosphere. Since the heat flux electron strahl always flows away from the Sun, a heat flux dropout should indicate either that the magnetic field line is completely disconnected from the Sun or that the heat flux strahl is scattered into other pitch angles. We present observations of two suprathermal electron heat flux dropout events observed by the Advanced Composition Explorer (ACE) spacecraft which occur simultaneously with impulsive energetic ion events. Since suprathermal electrons encompass the same velocity range as ions with energies of a few MeV/nucleon, the similarities and differences between them as observed at 1 AU probes the sources and transport of these two species. We compare the two events to show the difference between the signatures of a simple disconnection and a more complicated reconnection scenario. Comparing suprathermal electron modulations with energetic ion modulations is a powerful technique for determining the magnetic topology between particle injection at the Sun and observation at 1 AU. © 2010 American Institute of Physics.
• Giacalone, J. (2010). The acceleration of inner-source pickup ions by a propagating interplanetary shock. AIP Conference Proceedings, 1302, 119-124.
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  Abstract: We apply test-particle numerical simulations to model the acceleration of inner-source C+ by a strong interplanetary shock. The model consists of three distinct parts: (a) the distribution of inner-source pickup ions; (b) the initial acceleration of pickup ions (to produce seed particles) for a kinematically defined interplanetary shock; and (c) the acceleration to higher energies and the resulting event-averaged energy spectrum seen by an observer at 1 AU based on the solution to the Parker transport equation for a propagating shock. Our results are compared with observational estimates of the upper bound on the spectrum of C+ ions associated with the Aug. 25, 1998 solar-energetic particle event. Our calculated spectrum is very close to this upper-bound estimate, suggesting that the intensity of accelerated C+ is just at the sensitivity of measurement. © 2010 American Institute of Physics.
• Giacalone, J., & Burgess, D. (2010). Interaction between inclined current sheets and the heliospheric termination shock. Geophysical Research Letters, 37(19).
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  Abstract: Using two-dimensional hybrid simulations we study the interaction between the Heliospheric Current Sheet (HCS) and the solar wind termination shock (TS). Hot flow anomalies (HFA) are regions of hot, deflected and disturbed plasma flow which may form at the intersection of a shock and current sheet. We study the role played by the inclination, θCn, of the current sheet relative to the shock normal. As previously found, low values of θCn are associated with HFA formation. We find that as θCn increases the HFA is modified, until at θCn = 60 it disappears completely. Thus, HFAs are unlikely to be formed near the TS since the HCS is highly inclined relative to the radial direction (θCn > 60). We also find that some suprathermal particles, particularly interstellar pickup ions, are trapped near the intersection point of the shock and current sheet where they gain considerable energy, and subsequently drift along the current sheet upstream of the shock. This process is more effective for larger values of θCn. Thus, we expect that upstream of the TS there are likely to be high-energy particles (energized pickup ions) associated with crossings of the HCS, but only of the particular magnetic reversal polarity associated with HFAs. This may be relevant to recently reported Voyager observations. © 2010 by the American Geophysical Union.
• Giacalone, J., & Decker, R. (2010). The origin of low-energy anomalous cosmic rays at the solar-wind termination shock. Astrophysical Journal Letters, 710(1), 91-96.
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  Abstract: We address the origin of the enhancement of ∼ 40keV to 5 MeV ions at the solar wind termination shock. Using self-consistent two-dimensional hybrid simulations (kinetic proton, fluid electron) of a shock moving through a plasma similar to that observed in the outer heliosphere, we conclude that the observed ion enhancements are consistent with accelerated "core" interstellar pickup ions (those that have not previously undergone any significant energization) by the termination shock via a combination of shock drift acceleration and particle scattering in meandering magnetic fields in the vicinity of the shock. In addition to the consequences for our understanding of anomalous cosmic rays, this work is also relevant to the more-general long-standing problem of accelerating low-energy particles by shocks that move nearly normal to a mean magnetic field. © 2010. The American Astronomical Society. All rights reserved.
• Guo, F., & Giacalone, J. (2010). The effect of large-scale magnetic turbulence on the acceleration of electrons by perpendicular collisionless shocks. Astrophysical Journal Letters, 715(1), 406-411.
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  Abstract: We study the physics of electron acceleration at collisionless shocks that move through a plasma containing large-scale magnetic fluctuations. We numerically integrate the trajectories of a large number of electrons, which are treated as test particles moving in the time-dependent electric and magnetic fields determined from two-dimensional hybrid simulations (kinetic ions and fluid electron). The large-scale magnetic fluctuations effect the electrons in a number of ways and lead to efficient and rapid energization at the shock front. Since the electrons mainly follow along magnetic lines of force, the large-scale braiding of field lines in space allows the fast-moving electrons to cross the shock front several times, leading to efficient acceleration. Ripples in the shock front occurring at various scales will also contribute to the acceleration by mirroring the electrons. Our calculation shows that this process favors electron acceleration at perpendicular shocks. The current study is also helpful in understanding the injection problem for electron acceleration by collisionless shocks. It is also shown that the spatial distribution of energetic electrons is similar to in situ observations. The process may be important to our understanding of energetic electrons in planetary bow shocks and interplanetary shocks, and explaining herringbone structures seen in some type II solar radio bursts. © 2010. The American Astronomical Society. All rights reserved.
• Hsieh, K. C., Giacalone, J., Czechowski, A., Hilchenbach, M., Grzedzielski, S., & Kota, J. (2010). Thickness of the heliosheath, return of the pick-up ions, and voyager 1's crossing the heliopause. Astrophysical Journal Letters, 718(2 PART 2), L185-L188.
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  Abstract: abs Using results of remote sensing by energetic neutral atoms from IBEX, SOHO/HSTOF, and Cassini/INCA, in situ measurements of ∼40-4000 keV protons in the heliosheath (HS) from Low Energy Charged Particle on Voyager 1 and Voyager 2, and outputs from numerical modeling of the termination shock, we estimate L, the characteristic thickness of the HS in the "upwind" direction (±45° in ecliptic longitude of the Nose at λ = 255°). A simple steady-state, internally consistent model gives L = 21 ± 6 AU for Voyager 1, L = 28 ± 8 AU for Voyager 2, and L = 25 ± 8 AU assuming that the same L value is valid for both spacecraft. We recognize that this is a very coarse cut at a very dynamic region of the heliosphere; but if the lower value L = 21 AU applies, one could expect Voyager 1 to cross the heliopause as early as late 2010. © 2010. The American Astronomical Society.
• Jokipii, J. R., Giacalone, J., Hsieh, K. C., & Kóta, J. (2010). The structure of the IBEX ribbon: A reflection of interstellar turbulence?. AIP Conference Proceedings, 1302, 92-97.
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  Abstract: We discuss the structure of the "ribbon" seen in the energetic-neutral-atom (ENA) maps obtained from the IBEX HI instrument. We work with the interpretation that the ribbon is the result of 2nd-generation pickup ions "trapped" in the interstellar magnetic field because their motion is very-nearly normal to the field [1][2]. The process of charge exchange in the solar wind, which produces the observed 'pickup' ions produces in addition to the ion, a neutral hydrogen atom with the solar wind velocity. These 'solar-wind neutrals', which we term 'SWN' move radially outward into the local interstellar medium. They have a probability of being ionized a second time and will then again respond to the ambient, fluctuating interstellar magnetic field. The magnetic field acts in two ways to concentrate the ions so created in the direction normal to the interstellar magnetic field. First, any ions created by stripping will build up to a very high intensity where they are moving normal to the essentially static magnetic field. Second, the subsequent third charge exchange which produces an ENA must involve a particle gyrating around the magnetic field in a plane including the Sun. Both of these effects will act to produce 2nd-generation ENAs moving toward the inner heliosphere. We suggest that fluctuations in the direction of the interstellar turbulent magnetic field on the scale of the ribbon will contribute significantly to the observed width of the ribbon and to the observed temporal variations. © 2010 American Institute of Physics.
• Neugebauer, M., & Giacalone, J. (2010). Progress in the study of interplanetary discontinuities. AIP Conference Proceedings, 1216, 194-197.
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  Abstract: This paper summarizes some of the recent rebirth of interest in interplanetary discontinuities. Vasquez et al. have developed a new method of searching for discontinuities that allows the study of structures with small angles of rotation. Those discontinuities are consistent with the in situ generation of discontinuities by Alfvénic turbulence. Borovsky has proposed that discontinuities with large rotation angles are the boundaries of flux tubes originating at the Sun. We conclude that both the Sun and turbulence are important sources of interplanetary discontinuities. We also argue that, at least in the slow solar wind, Tsurutani's in-situ generation by phase-steepened Alfvén waves may be a manifestation of exhaust fan reconnection. We furthermore suggest that such reconnection may be responsible for the Walen ratio ([4πρ]1/2|Δv|/|ΔB|) across rotational discontinuities being less than the theoretically predicted value of unity. Whether or not the wind consists of discrete flux tubes rather than being simply discontinuous remains to be determined. © 2010 American Institute of Physics.
• Chollet, E. E., Giacalone, J., Skoug, R. M., Steinberg, J. T., & Gosling, J. T. (2009). Spatial offsets of interplanetary ion and electron source regions. Astrophysical Journal Letters, 705(2), 1492-1495.
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  Abstract: Observations of impulsive solar energetic particles provide unique insight into the process of particle acceleration in the solar atmosphere. X-ray and γ-ray observations of precipitating particles from solar flares have shown offsets between the ion and the electron emission. We present Advanced Composition Explorer (ACE) observations of interplanetary energetic ion and suprathermal electron events with intensity variations related to connection or lack thereof to the particle source. These results indicate an offset between the acceleration regions of ions and electrons of the same order of magnitude as that observed in the γ-ray events. However, if the particle event originates at the magnetic footpoints of an interplanetary coronal mass ejection, the ACE observations do not exhibit this offset, suggesting that different magnetic geometry or acceleration processes may be present in those regions. © 2009. The American Astronomical Society. All rights reserved.
• Giacalone, J., & Jokipii, J. R. (2009). The acceleration of stationary charged dust grains by propagating collisionless shock waves. Astrophysical Journal Letters, 701(2), 1865-1871.
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  Abstract: We consider the acceleration of charged particles, which are initially completely at rest with respect to the local upstream plasma rest frame, by collisionless shocks propagating through a static, irregular magnetic field. A relevant example is the interaction of cold, charged interstellar dust grains with a shock associated with a supernova blast wave propagating through the fluctuating interstellar magnetic field. We treat the dust grains as test particles moving under the influence of electromagnetic forces arising from a magnetic field which has an average plus a fluctuating part, and is static in the local plasma frame. The only electric field is that which arises from the flow of plasma across the magnetic field. We find that a significant fraction of the dust grains are accelerated to more than 10 times the shock speed within 100 cyclotron periods. The percentage of those incident on the shock that are accelerated depends strongly on the turbulence variance, but is essentially independent of average shock-normal angle provided the fluctuation amplitude is of the same order as the mean. Our results are relevant to the "injection problem" in shock acceleration of charged particles. © 2009 The American Astronomical Society. All rights reserved.
• Hsieh, K. C., Frisch, P. C., Giacalone, J., Jokipii, J. R., Kóta, J., Larson, D. E., Lin, R. P., Luhmann, J. G., & Wang, L. (2009). A re-interpretation of STEREO/STE observations and its consequences. Astrophysical Journal Letters, 694(1 PART 2), L79-L82.
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  Abstract: We present an alternate interpretation of recent STEREO /STE observations which were attributed to energetic neutral atoms (ENAs) from the heliosheath. The inferred ENA intensities, as a function of longitude, are very similar to the instrument response, implying that the source or sources are quite narrow. Such narrow sources may be quite difficult to ascribe to the available sources of ENAs, such as the charge exchange of energetic charged particles with ambient neutrals, which tend to be much broader. We point out that the largest intensity maximum observed by STEREO/STE is centered at the same ecliptic longitude as the brightest known X-ray source, Sco X-l. If this is indeed the source of the detected flux, it naturally accounts for the small source width. We find that the observed energy spectrum and intensity are also consistent with the X-rays from Sco X-l. If this interpretation is correct, then observers must take care in analyzing ENA data based on detectors sensitive to radiation other than ENAs. The problem of energy dissipation in the solar wind termination shock remains unsolved, while current understanding of the interaction between the solar wind and interstellar wind awaits future observations. ©2009. The American Astronomical Society. All rights reserved.
• Chollet, E. E., & Giacalone, J. (2008). Multispacecraft analysis of energetic ion flux dropouts. Astrophysical Journal, 688(2), 1368-1373.
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  Abstract: We present an analysis of dispersionless flux dropouts in solar energetic particles (SEPs) associated with impulsive solar flares observed by ACE/ULEIS and Wind/STEP. These flux dropouts are thought to be caused by an observer encountering magnetic field lines that are populated with particles or unpopulated, depending on their connection to the source. Since ACE and Wind typically have spatial separations less than or of order a correlation scale of the turbulent component of the interplanetary magnetic field (Lc ∼ 106 km), they are ideal for studying the effects of the turbulent magnetic field on impulsive SEP events, especially those that exhibit intensity dropouts. By examining the timing of the dropout events seen by each spacecraft and accounting for the convection of frozen-in magnetic fields by the solar wind, we have found that both spacecraft generally see the same event features when they are separated by less than Lc and different features when they are separated by more than Lc. This is consistent with the propagation of impulsive SEPs along random walking magnetic lines of force. We find that dropouts occur in approximately half of the impulsive SEP events in our sample, indicating that this is a fairly common phenomenon. Moreover, we find that there is not a clear correspondence between the timing of these events and changes in the local interplanetary magnetic field more often than random coincidence. This supports the idea that intensity dropouts are mostly caused by field line mixing rather than by localized magnetic structures. © 2008. The American Astronomical Society. All rights reserved.
• Giacalone, J. (2008). Particle acceleration at a perpendicular shock in the limit of weak pitch-angle scattering. AIP Conference Proceedings, 1039, 227-232.
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  Abstract: We discuss the physics of charged-particle acceleration at nearly perpendicular shocks focusing on the limit of weak pitch-angle scattering. Recent observations of large anisotropics of energetic particles upstream of the solar-wind termination shock suggest the particles are very weakly scattered. This raises questions about how rapidly the particles are accelerated by the shock, and whether there is a significant injection problem. We perform new numerical simulations of test protons accelerated by a synthesized termination shock. In our model, the turbulent magnetic field is generated by summing over a large number of discrete plane waves with amplitudes determined from a specified power spectrum and random phases and propagation directions. We study the effect of removing magnetic fluctuations with scales that resonate with the particles in order to model the case where the scattering is very weak (long parallel mean-free paths). Field-line meandering, which we have previously found to be important at quasi-perpendicular shocks, is included. The results are discussed in the context of the Voyagers observations as well as fundamental theory of diffusive shock acceleration. Our primary conclusion is that by removing the short wavelength magnetic fluctuations the efficiency of particle acceleration at the shock is greatly reduced. © 2008 American Institute of Physics.
• Giacalone, J., & Neugebauer, M. (2008). The energy spectrum of energetic particles downstream of turbulent collisionless shocks. Astrophysical Journal, 673(1), 629-636.
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  Abstract: Using simple analytic considerations, numerical simulations, and data analysis, we discuss the physics of charged-particle acceleration by turbulent, rippled, collisionless shocks. The standard theory of diffusive shock acceleration predicts that the energetic-particle energy spectrum, in the region of shocked plasma, is a function of the plasma density jump. But because of the interaction of the shock with plasma turbulence, the jump in plasma density varies in time and from place to place on the shock front. Here we show that for reasonable parameters, the shape of the energetic-particle energy spectra downstream of any given shock is nearly independent of location along the shock front, even though the density jump varies. This is because energetic particles are mobile and sample many turbulent fluctuations during their acceleration. This result holds for shocks having smaller scale ripples than the large-scale radius of curvature (Dc) of the shock. Thus, it applies to the interpretation of spacecraft observations of traveling interplanetary shocks provided the spacecraft separation is less thanDc. This result is confirmed with simple analytic considerations and numerical simulations that solve the combined magnetohydrodynamic equations for a plasma and energetic test particles using the well-known Parker transport equation. This conclusion is further supported by our analysis of ACE and Geotail observations of a few interplanetary shocks. © 2008. The American Astronomical Society. AU rights reserved.
• Mewaldt, R. A., Cohen, C. M., Giacalone, J., Mason, G. M., Chollet, E. E., Desai, M. I., Haggerty, D. K., Looper, M. D., Selesnick, R. S., & Vourlidas, A. (2008). How efficient are coronal mass ejections at accelerating solar energetic particles?. AIP Conference Proceedings, 1039, 111-117.
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  Abstract: The largest solar energetic particle (SEP) events are thought to be due to particle acceleration at a shock driven by a fast coronal mass ejection (CME). We investigate the efficiency of this process by comparing the total energy content of energetic particles with the kinetic energy of the associated CMEs. The energy content of 23 large SEP events from 1998 through 2003 is estimated based on data from ACE, GOES, and SAMPEX, and interpreted using the results of particle transport simulations and inferred longitude distributions. CME data for these events are obtained from SOHO. When compared to the estimated kinetic energy of the associated coronal mass ejections (CMEs), it is found that large SEP events can extract ∼10% or more of the CME kinetic energy. The largest SEP events appear to require massive, very energetic CMEs. © 2008 American Institute of Physics.
• Chollet, E. E., Giacalone, J., Mazur, J. E., & Dayeh, M. A. (2007). A new phenomenon in impulsive-flare-associated energetic particles. Astrophysical Journal, 669(1), 615-620.
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  Abstract: We present ACE/ULEIS and Wind/STEP observations of a new and unusual feature of energetic ions between 0.02 and 3 MeV nucleon-1 associated with impulsive solar flares. In addition to the usual velocity dispersion associated with the transit in the heliospheric magnetic field of energetic particles from a small localized source on the Sun, these events also show intermittent behavior that may be related to the magnetic flux tube structure of the solar wind. These are anomalous bursts of low-energy particles, which we call "tassels." Tassels are enhancements of ions extending to much lower energies than those associated with the main event. In one year of data from 2000 June to 2001 July, we have identified two events with tassels, both of which occur simultaneously with interplanetary coronal mass ejections (ICMEs). The tassels may be a superposition of two events, either gradual and impulsive or two impulsive events. Since the tassels could be interpreted as ions arriving earlier than those with the same energy in the main velocity dispersion, we suggest that the tassels occur when the spacecraft intercepts a flux tube with a relatively shorter path length. The decrease in path length may be caused by a decrease in scattering or a shorter travel distance, since flux tubes may be distorted by the passage of the ICME. These tassel events may allow us to infer some of the structure of the ICME. © 2007. The American Astronomical Society. All rights reserved.
• Giacalone, J., & Jokipii, J. R. (2007). Large-scale turbulence, shocks, and charged-particle acceleration. AIP Conference Proceedings, 932, 243-257.
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  Abstract: We discuss the physics of particle acceleration by shocks moving in turbulent astrophysical plasmas. We suggest that the observed lack of agreement of energetic particles and shock properties in the heliosphere is likely to be a result of fluctuations and turbulence in the upstream fluid. Shock acceleration takes time, so the observations of particles at any given point and time at a shock reflects some combination of the history prior to the time of observation. Further, since the particles are mobile, there is spatial averaging as well. It follows that the shock properties observed by a spacecraft should not correlate well with the accelerated particles. Additionally, the upstream turbulence, and in particular, the fluctuations in plasma density have a large effect on the downstream magnetic field. These effects may also help to understand the magnetic field observed by Voyager 1 in the heliosheath. © 2007 American Institute of Physics.
• Giacalone, J., & Jokipii, J. R. (2007). Magnetic field amplification by shocks in turbulent fluids. Astrophysical Journal, 663(1 II), L41-L44.
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  Abstract: We consider the effect of preexisting, large-scale, broadband turbulent density fluctuations on propagating hydromagnetic shock waves. We present results from several numerical simulations that solve the two-dimensional magnetohydrodynamic equations. In our simulations, a plasma containing large-scale, low-amplitude density and magnetic field turbulence is forced to flow into a rigid wall, forming a shock wave. We find that the density fluctuations not only distort the shape of the shock front and lead to a turbulent postshock fluid, but they also produce a number of important changes in the postshock magnetic field. The average downstream magnetic field is increased significantly, and large fluctuations in the magnetic vector occur, with the maximum field strength reaching levels such that magnetic stresses are important in the postshock region. The downstream field enhancement can be understood in terms of the stretching and forcing together of the magnetic field entrained within the turbulent fluid of the postshock flow. We suggest that these effects of the density fluctuations on the magnetic field are observed in astrophysical shock waves such as supernova blast waves and the heliospheric termination shock. © 2007. The American Astronomical Society. All rights reserved.
• Jokipii, J. R., & Giacalone, J. (2007). Adiabatic compression acceleration of fast charged particles. Astrophysical Journal, 660(1 I), 336-340.
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  Abstract: In this paper we introduce a mode of acceleration of fast, low-rigidity charged particles at shocks and compressions which does not appear to have been discussed previously. The particles propagate along the fluctuating magnetic field without scattering. The acceleration occurs when the disturbance propagates normal to a magnetic field which is turbulent on large scales. If the low-rigidity particles have speeds much greater than the speed of the disturbance, they can follow the random magnetic field lines, which meander back and forth across the compression. Because of the difference between the downstream and upstream flow speeds, the particles can be accelerated, much as in standard diffusive shock acceleration. In this picture, scattering in pitch angle is not necessary for considerable acceleration to occur. We suggest that this completely scatter-free process may accelerate low-energy superthermal electrons, for which resonant scattering may not be possible, up to energies where they can interact resonantly with longer wave-length waves generated by the ions and subsequently be accelerated by standard diffusive shock acceleration to energies comparable with the ions. © 2007. The American Astronomical Society, All rights reserved.
• Jokipii, J. R., Giacalone, J., & Kóta, J. (2007). The physics of particle acceleration at the heliospheric termination shock. Planetary and Space Science, 55(15), 2267-2272.
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  Abstract: Cosmic rays are ubiquitous in space, and the essential similarity of their energy spectra in many different regions places significant general constraints on the mechanisms for their acceleration and confinement. Diffusive shock acceleration is at present the most successful acceleration mechanism proposed, and, together with transport in Kolmogorov turbulence, can account for the universal specta. A unique laboratory for studying the acceleration and transport of charged particles is the outer heliosphere, including the solar wind termination shock and heliosheath. A widely accepted paradigm for the transport and acceleration of energetic particles in the heliosphere has evolved over the last few decades. This picture has successfully explained many features of the modulation of galactic cosmic rays and the transport and acceleration of anomalous cosmic rays at the solar-wind termination shock. Recent Voyager observations near and beyond the termination shock have revealed new, and in some cases, unexpected phenomena which have led to questions concerning the established paradigm. The physical interpretation of the observations requires a blunt termination shock, rapid inward motion of the shock and temporal variations over time scales ranging from hours to 22 years. Incorporation of these into the physics has promise of explaining most, if not, all of the observed phenomena while retaining the advantages of the termination shock paradigm for both galactic and anomalous cosmic rays. © 2007.
• Roberts, D. A., Giacalone, J., Jokipii, J. R., Goldstein, M. L., & Zepp, T. D. (2007). Spectra of polar heliospheric fields and implications for field structure. Journal of Geophysical Research A: Space Physics, 112(8).
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  Abstract: The predictions of the "Fisk" model for a peak at the equatorial solar rotation frequency in the spectrum of the latitudinal component of the heliospheric magnetic field were found to give values significantly larger than those observed. The observed values were statistically the same as observed in the ecliptic and were consistent with random fluctuations about the (null) Parker field component. These conclusions are based on spectra of field and plasma quantities using Ulysses data from the first southern and northern polar passes. There was also no evidence for solar photospheric differential rotation in the latitudinal component. A related search for signatures of the differential rotation (not directly part of the Fisk magnetic field model) yielded the strongest evidence for a photospheric influence on the radial component of the solar wind velocity and related "compressive" quantities. Copyright 2007 by the American Geophysical Union.
• Carr, C. M., Horbury, T. S., Balogh, A., Bale, S. D., Baumjohann, W., Bavassano, B., Breen, A., Burgess, D., Cargill, P. J., Crooker, N., Erdös, G., Fletcher, L., Forsyth, R. J., Giacalone, J., Glassmeier, K. -., Hoeksema, J. T., Goldstein, M. X., Lockwood, M., Magnes, W., , Maksimovic, M., et al. (2006). A magnetometer for the Solar Orbiter Mission. European Space Agency, (Special Publication) ESA SP.
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  Abstract: The magnetometer is a key instrument to the Solar Orbiter mission. The magnetic field is a fundamental parameter in any plasma: a precise and accurate measurement of the field is essential for understanding almost all aspects of plasma dynamics such as shocks and stream-stream interactions. Many of Solar Orbiter's mission goals are focussed around the links between the Sun and space. A combination of in situ measurements by the magnetometer, remote measurements of solar magnetic fields and global modelling is required to determine this link and hence how the Sun affects interplanetary space. The magnetic field is typically one of the most precisely measured plasma parameters and is therefore the most commonly used measurement for studies of waves, turbulence and other small scale phenomena. It is also related to the coronal magnetic field which cannot be measured directly. Accurate knowledge of the magnetic field is essential for the calculation of fundamental plasma parameters such as the plasma beta, Alfven speed and gyroperiod. We describe here the objectives and context of magnetic field measurements on Solar Orbiter and an instrument that fulfils those objectives as defined by the scientific requirements for the mission.
• Giacalone, J., & Jokipii, J. R. (2006). Energetic particle intensities and anisotropies near the solar wind termination shock. Astrophysical Journal Letters, 649(2 II), L137-L140.
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  Abstract: We address the physics of intensity and anisotropy variations in energetic particles near the solar wind termination shock. We show that rapid, large-amplitude, and highly anisotropic particle events seen upstream of the shock can be understood in terms of the passage across the spacecraft of different filled and unfilled magnetic flux tubes. These are created by large-scale magnetic irregularities that are advected passed the spacecraft and compress as they cross the termination shock. We find significant streaming anisotropies of 50 keV-1 MeV protons in the unshocked solar wind, with front-to-back intensity ratios exceeding a factor of 2, for 5 day averaged values. In contrast, downstream of the shock, our results indicate that the particle distributions are much more uniform and isotropic. However, there is a large-scale, nonzero azimuthal particle anisotropy downstream of the shock. This is caused by the nonradial heliosheath plasma flow necessitated by the nonspherical shock. Our results are consistent with recent Voyager 1 observations. © 2006. The American Astronomical Society. All rights reserved.
• Giacalone, J., & Jokipii, J. R. (2006). Shock acceleration of high-energy cosmic rays: The importance of the magnetic-field angle. Journal of Physics: Conference Series, 47(1), 160-167.
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  Abstract: The physics of particle acceleration by collisionless shocks is addressed using analytic theory and numerical simulations. In this paper we focus on the importance of the angle between the shock normal and upstream mean magnetic field, θBn, in determining the energy spectrum of the accelerated particles. We show that the acceleration rate is strongly dependent on θBn and is a maximum at perpendicular shocks. Moreover, we demonstrate that for a wide range of reasonable parameters, the acceleration effciency is weakly dependent on the shock normal angle. When applied to acceleration at supernovae blast waves, we find, therefore, for any given time interval, the highest-energy cosmic rays originate from regions in which the shock moves normal to the mean magnetic field. We also find that maximum energy is larger than that obtained using the well-known Bohm-limit. © 2006 IOP Publishing Ltd.
• Giacalone, J., & Jokipii, J. R. (2006). Test-particle numerical simulations of energetic particles near the termination shock. AIP Conference Proceedings, 858, 202-206.
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  Abstract: We present the results of recent non-diffusive test-particle numerical simulations of energetic-particle transport near the solar-wind termination shock. Here we focus on a distinct aspect of this problem: variations (spatial and temporal) in the intensities and anisotropies of low-energy protons (50 keV). Our simulations indicate that 50keV proton intensities are highly variable upstream of the shock with large anisotropies that are directed primarily away from the shock, whereas downstream of the shock, the intensity variations have a much smaller amplitude and the anisotropies are smaller. Our results are qualitatively consistent with recent Voyager 1 observations. © 2006 American Institute of Physics.
• Giacalone, J., & Kóta, J. (2006). Acceleration of solar-energetic particles by shocks. Space Science Reviews, 124(1-4), 277-288.
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  Abstract: Our current understanding of the acceleration of solar-energetic particles is reviewed. The emphasis in this paper is on analytic theory and numerical modeling of the physics of diffusive shock acceleration. This mechanism naturally produces an energy spectrum that is a power law over a given energy interval that is below a characteristic energy where the spectrum has a break, or a rollover. This power law is a common feature in the observations of all types of solar-energetic particles, and not necessarily just those associated with shock waves (e.g. events associated with impulsive solar flares which are often described in terms of resonant stochastic acceleration). Moreover, the spectral index is observed to have remarkably little variability from one event to the next (about 50%). Any successful acceleration mechanism must be able to produce this feature naturally and have a resulting power-law index that does not depend on physical parameters that are expected to vary considerably. Currently, only diffusive shock acceleration does this. © Springer Science+Business Media, Inc. 2007.
• Hilchenbach, M., Orsini, S., Hseih, K. C., Antonucci, E., Barabash, S., Bamert, K., Bruno, R., Collier, M. R., Czechowski, A., D'Amicis, R., Angelis, E. D., Dandouras, I., Lellis, A. D., Esser, R., Giacalone, J., Gruntman, M., Habbal, S. R., Jokipii, J. R., Kallio, E., , Kota, J., et al. (2006). Solar orbiter neutral solar-wind detector. European Space Agency, (Special Publication) ESA SP.
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  Abstract: Neutral hydrogen atoms, which give rise to the prominent solar Ly-α corona, are closely coupled to the emerging solar-wind plasma. The density ratio of neutral hydrogen to protons is minute, ∼10-6; therefore, the neutral atoms are tracers in the solar wind. In-situ observations of the neutral atoms, their flight paths (imaging), density, and velocity distributions are a new tool to the understanding of the Ly-α corona, i.e. setting limits on the plasma velocity distribution along the solar magnetic field lines. The other goal of the neutral solar-wind instrumentation is the in-situ observation of the interactions between solar wind plasma and dust grains near the Sun. We will discuss the science objectives and the potential "zero charge" solar-wind instrument envelope onboard Solar Orbiter.
• Neugebauer, M., Giacalone, J., Chollet, E., & Lario, D. (2006). Variability of low-energy ion flux profiles on interplanetary shock fronts. Journal of Geophysical Research A: Space Physics, 111(12).
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  Abstract: Time-intensity profiles of 20-126 keV ions across interplanetary shocks are studied using data from ACE and Wind to determine the dependence of the profiles on spacecraft separation. Each pair of time-intensity profiles is examined to determine whether or not the same features (flat, classic energetic storm particle (ESP) rise, spikes, step functions, or complex patterns) are seen at both spacecraft. The persistence of particle profile patterns has a scale length in the plane of the shock of ∼2.9 Mkm, but the scale length along the shock normal direction is not well determined. Copyright 2006 by the American Geophysical Union.
• Pei, C., Jokipii, J. R., & Giacalone, J. (2006). Effect of a random magnetic field on the onset times of solar particle events. Astrophysical Journal Letters, 641(2 I), 1222-1226.
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  Abstract: We present the results of numerical simulations of solar energetic particles (SEPs) moving in a model helio-spheric magnetic field. We find that the onset time of a given SEP event can be sooner than estimated by assuming that particles move along the usual Parker spiral, which is generally believed to be the earliest time. This is because for a random magnetic field, some magnetic field lines are shorter than the nominal (Parker spiral) length. This is important with regard to the physics of injection and/or acceleration at the origin of the particle event. © 2006. The American Astronomical Society. All rights reserved.
• Giacalone, J. (2005). Particle acceleration at shocks moving through an irregular magnetic field. Astrophysical Journal Letters, 624(2 I), 765-772.
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  Abstract: We use nondiffusive, nonrelativistic, test-particle numerical simulations to address the physics of particle acceleration by collisionless shocks. We focus on the importance of the shock normal angle, (θBn), in determining the energy spectrum of the accelerated particles. For reasonable parameters, we find that the injection velocity is weakly dependent on the mean shock normal angle and that low-energy particles are readily accelerated to high energies irrespective of 〈θBn〉. Our results are applicable for shocks that are nearly planar on scales larger than the coherence scale of the upstream magnetic turbulence and for particles whose gyroradii are smaller than this scale. We confirm previous results showing that the acceleration rate is larger for nearly perpendicular shocks compared to parallel shocks. However, we also find that the acceleration rate at parallel shocks moving through large-scale magnetic fluctuations is larger than that predicted by simple first-order Fermi acceleration. Our results can be understood in terms of the nature of the large-scale fluctuations and their effect on particle transport. © 2005. The American Astronomical Society. All rights reserved.
• Giacalone, J. (2005). Particle acceleration in the sun and heliosphere. European Space Agency, (Special Publication) ESA SP, 55-60.
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  Abstract: Our current understanding of the acceleration of energetic charged particles of heliospheric origin is reviewed. This paper outlines the key points, topics, and open issues that were discussed in the tutorial talk on energetic particles in the Sun and heliosphere. Because of the broad scope of this topic, much of the review focused on solar energetic particles. Moreover, while a few acceleration mechanisms were discussed, much of the emphasis was placed on the physics of diffusive shock acceleration. This mechanism naturally leads to power-law energy spectra which are commonly observed in the distributions of energetic particles in space plasmas. The theme of the tutorial was that the energy spectrum of most solar-energetic particle events, as well as other energetic nuclei of heliospheric origin, and galactic cosmic rays, share one common characteristic: they are all power laws below a characteristic energy. Moreover, the spectral index does not vary much from one event to the next. Any successful acceleration mechanism must be able to produce this feature naturally. Currently, only diffusive shock acceleration does this.
• Giacalone, J. (2005). The efficient acceleration of thermal protons by perpendicular shocks. Astrophysical Journal Letters, 628(1 II), L37-L40.
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  Abstract: The physics of charged-particle acceleration from near-thermal to much higher energies by collisionless shocks is investigated using large-scale self-consistent plasma simulations. The focus here is on acceleration at shocks that move normal to the average magnetic field. It is shown that a fraction of thermal protons incident on a perpendicular shock are readily accelerated to energies much higher than the ram energy of the incident plasma. This indicates that there is not an injection problem at perpendicular shocks. It is found that some (initially) thermal protons are reflected by the shock and move upstream along magnetic field lines that are multiply connected to other locations on the shock. This leads to efficient acceleration and results in a distribution function, averaged over a large spatial region downstream of the shock, having a high-energy tail that originates directly from the thermal population. It can be concluded from our results that perpendicular shocks are important sites of particle acceleration in a wide variety of astrophysical plasmas. © 2005. The American Astronomical Society. All rights reserved.
• Giacalone, J. (2005). The importance of field-line meandering in particle acceleration at shocks. AIP Conference Proceedings, 781, 213-218.
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  Abstract: We discuss the physics of particle acceleration by shocks emphasizing the importance of the large-scale fluctuating magnetic field. In particular, we discuss the implications for shock acceleration of large cross-field transport due to particles moving nearly along meandering magnetic field lines. It is found that this effect significantly aids in the acceleration of low-energy particles at perpendicular shocks and that there is no injection problem. New results from test particle and self-consistent "hybrid" simulations are presented that support this. © 2005 American Institute of Physics.
• Jokipii, J. R., Kóta, J., & Giacalone, J. (2005). Magnetic field structure and ACR acceleration at the termination shock. European Space Agency, (Special Publication) ESA SP, 23-28.
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  Abstract: Anomalous cosmic rays are thought to be accelerated at the termination shock of the solar wind. Voyager 1 observations in the outer heliosphere, upstream of the termination shock and, recently, in the heliosheath impose important constraints on anomalous cosmic rays (ACR) acceleration at the heliospheric termination shock. Here we summarize the three-dimensional, vector anisotropies (radial, azimuthal and latitudinal) of the ACR and show how they depend on the large-scale structure of termination shock. The observations can be understood if the shape of the termination shock is not spherical, both globally and on a small scale. We also discuss the effects of radial motion of the termination shoe. This can alter the magnetic structure and change the intensity and energy spectra both upstream of the shock and in the heliosheath. Recent observations of the magnetic field from the Voyager 1 spacecraft, where, in the heliosheath, the magnetic field has remained directed outward from the Sun for several months suggest that the shock is moving rapidly inward. The implications for the energy spectrum of the ACR are also discussed.
• Mewaldt, R. A., Cohen, C. M., Mason, G. M., Haggerty, D. K., Looper, M. D., Vourlidas, A., Desai, M. I., Giacalone, J., Labrador, A. W., Leske, R. A., & Mazur, J. E. (2005). How efficient are coronal mass ejections at accelerating solar energetic particles?. European Space Agency, (Special Publication) ESA SP, 67-70.
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  Abstract: The largest solar energetic particle (SEP) events are thought to be caused by shocks driven by fast coronal mass ejections (CMEs). We study the efficiency of this process by comparing the energy content of energetic particles in large SEP events to the kinetic energy of the associated CMEs. The SEP observations are from 17 events observed by ACE, SAMPEX, and GOES during 1998-2003 and the CME observations are from SOHO. In situ solar-wind data show that CME kinetic energy estimates from SOHO/LASCO for the October 28, 2003 event are much more accurate than those from SMEI. The ratio of SEP to CME kinetic energies is found to range from ∼0.1% to ∼20%. The largest SEP events have an average SEP/CME kinetic-energy ratio of ∼10%, similar to that estimated for cosmic-ray acceleration by supernova shocks.
• Neugebauer, M., & Giacalone, J. (2005). Multispacecraft observations of interplanetary shocks: Nonplanarity and energetic particles. Journal of Geophysical Research A: Space Physics, 110(A12).
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  Abstract: Numerical simulations of the evolution of interplanetary shocks exhibit growth of distortions of the shock front and nonuniformity of energetic particles from place to place near the shock surface. In this work we use multispacecraft (ACE, Wind, IMP 8, Geotail, Interball-Tail, SOHO, and Genesis) observations near Earth to search for such effects. On scales of 105 to 106 km, most of the 26 shocks studied were inconsistent with planar structures or with spherical structures with a radius of 1 AU. The average local radius of curvature was ∼3 × 106 km. There were also differences in the intensities and time profiles of energetic particle fluxes seen at both ACE and Wind. Cpyright 2005 by the American Geophysical Union.
• Giacalone, J. (2004). Large-scale hybrid simulations of particle acceleration at a parallel shock. Astrophysical Journal Letters, 609(1 I), 452-458.
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  Abstract: Using one-dimensional hybrid simulations with very large spatial domains, we study the acceleration of protons by a parallel collisionless shock to energies higher than have been obtained previously with self-consistent plasma simulations of this type. Energy spectra and energetic particle fluxes are determined for four simulations with different-sized spatial domains. We find that the density of energetic particles upstream decays with distance from the shock and approaches a constant. The energetic particles also excite magnetic fluctuations. We find that the variance of these transverse fluctuations decreases with distance from the shock into the upstream region. This implies that the mean free path, λ, of the energetic particles increases with distance from the shock. Since our simulations are spatially limited, the downstream energy spectra are expected to deviate from a power law and become exponential at a characteristic energy Ec. However, we find that because λ increases with distance upstream, Ec is smaller than expected from a simple application of the diffusive theory (which assumes a constant mean free path and a free-escape boundary). Our results are qualitatively consistent with diffusive theories of the coupling of the particles and self-generated waves. However, in contrast to these theories, the hybrid-simulated energetic particle flux approaches a constant at some point far upstream, rather than vanishing, as assumed in the diffusion theory.
• Giacalone, J., & Jokipii, J. R. (2004). Magnetic footpoint diffusion at the Sun and its relation to the heliospheric magnetic field. Astrophysical Journal Letters, 616(1 I), 573-577.
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  Abstract: We discuss the physics associated with the motion of the radial magnetic field footpoints at the Sun and its relation to the heliospheric magnetic field. Using the observed photospheric convection spectrum, we construct a model for the heliospheric magnetic field and relate it to observations made by Ulysses in the outer heliosphere in the fast solar wind during solar minimum. We find excellent agreement between both the magnitude and the radial variation of the large-scale transverse magnetic variance observed by Ulysses compared to the model calculations using the observed supergranulation velocity spectrum. This suggests that the model represents the physics well. We then calculate the spatial diffusion coefficient associated with the observed magnetic footpoint motion at the solar photosphere. The calculations are based on the motion of passive additives embedded within the transverse photospheric flows. Two different models for the temporal evolution of the transverse velocity are considered. We find that the diffusion coefficient associated with these motions is in the range κ ≈ 1500-1920 km2 s-1. This is approximately 3 times larger than is commonly used in models of the long-term solar magnetic field. It is also larger than is inferred from actual measurements of the dispersion of magnetic features on the Sun. The cause of this discrepancy is not yet clear.
• Jokipii, J. R., & Giacalone, J. (2004). Radial streaming anisotropies of charged particles accelerated at the solar wind termination shock. Astrophysical Journal Letters, 605(2 II), L145-L148.
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  Abstract: Recent observations of an increase in energetic particle intensities on the Voyager 1 spacecraft, for several months in late 2002 to early 2003, suggest new phenomena associated with its approach to the termination shock of the solar wind. An important diagnostic used by the experimenters to interpret the event has been the radial anisotropy of the energetic particle distribution. In this Letter we consider the transport of energetic charged particles accelerated at the termination shock, both in the diffusion approximation and by directly integrating test particle trajectories in a turbulent magnetic field. We determine the radial anisotropy in a number of models. In general, we find that the radial anisotropy of the particles is complicated and that it cannot reliably be used to determine the radial velocity of the background plasma. In all cases considered, we find that the average radial anisotropy in the region upstream of the shock is directed toward the shock and is less than or equal to the Compton-Getting anisotropy in the slower wind downstream. We attribute the difference from the Compton-Getting anisotropy to the diffusive anisotropy, which is directed upstream away from the shock and which is part of the acceleration process. We suggest that the small radial anisotropy observed on Voyager 1 at low energies may actually be an indication that Voyager 1 was located upstream of the shock during the entire event. In addition, we find large fluctuating anisotropies along the magnetic field (nearly transverse to the radial direction).
• Jokipii, J. R., Giacalone, J., & Kóta, J. (2004). Transverse streaming anisotropies of charged particles accelerated at the solar wind termination shock. Astrophysical Journal Letters, 611(2 II), L141-L144.
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  Abstract: We address the anisotropy, transverse to the heliographic radial direction, of energetic charged particles accelerated at the termination shock of the solar wind. We consider the transport of energetic charged particles both in the diffusion approximation and by directly integrating test particle trajectories in a turbulent magnetic field. We find that the nature and directions of the transverse anisotropies observed on Voyager 1 can be interpreted in terms of existing models of the heliosphere, if Voyager 1 were still upstream of the termination shock. In particular, the observations are consistent with recent models in which either the upstream heliospheric termination shock flares out from the nose of the heliosphere, so that its heliocentric radius increases away from the nose, or the heliosphere is offset from the direction of the incoming neutral wind, or both. In these pictures a Parker spiral magnetic field line from the Sun intersects the termination shock many times, not just once, and the closest intersection to Voyager 1 is on the direction along the field that leads back to the Sun, as is observed. We suggest that the recent Voyager 1 observations of energetic particle anisotropies, both radial and transverse, are expected in a scenario in which Voyager 1 did not cross the termination shock.
• Lembege, B., Giacalone, J., Scholer, M., Hada, T., Hoshino, M., Krasnoselskikh, V., Kucharek, H., Savoini, P., & Terasawa, T. (2004). Selected problems in collisionless-shock physics. Space Science Reviews, 110(3-4), 161-226.
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  Abstract: The physics of collisionless shocks is a very broad topic, which has been well studied for many decades. However, there are a number of important issues which remain unresolved. Moreover, there have been new findings, which cast doubt on well-established ideas. The purpose of this review is to address a subset of unresolved problems in collisionless shock physics from a theoretical and/or numerical modeling point of view. The topics which are addressed are: the nonstationarity of the shock front, the heating and dynamics of electrons through the shock layer, particle diffusion in turbulent electric and magnetic fields, particle acceleration, and the interaction of pickup ions with collisionless shocks.
• Giacalone, J. (2003). The physics of particle acceleration by collisionless shocks. Planetary and Space Science, 51(11), 659-664.
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  Abstract: Using analytic theory, test-particle simulations, and self-consistent hybrid simulations, we show that quasi-perpendicular shocks - those which propagate nearly perpendicular to the upstream magnetic field - accelerate particles directly out of the incident thermal population to energies much higher than the upstream ram energy of the plasma. It has already been established that quasi-parallel shocks - those which propagate nearly in the same direction as the upstream magnetic field - efficiently accelerate particles directly out of the incident thermal population; however, this has not yet been established for quasi-perpendicular shocks. Our results can be understood within the framework of the diffusive shock acceleration theory. We find that the accelerated-particle spectrum obtained from a more-general self-consistent hybrid plasma simulation are quantitatively consistent with a less-sophisticated test-particle simulation. The implications of this are discussed. © 2003 Elsevier Ltd. All rights reserved.
• Zhang, M., McKibben, R. B., Lopate, C., Jokipii, J. R., Giacalone, J., Kallenrode, M. -., & Rassoul, H. K. (2003). Ulysses observations of solar energetic particles from the 14 July 2000 event at high heliographic latitudes. Journal of Geophysical Research A: Space Physics, 108(A4).
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  Abstract: At the time of the solar flare on the Bastille Day of2000, the Ulysses spacecraft was at 3.17 AU from the Sun, 62° south in heliographic latitude, and 116° in longitude east of the Earth. Solar wind and magnetic field measurements by Ulysses indicate that the coronal mass ejection (CME) of this event had a limited size in both latitude and longitude, although it was a halo CME as seen in the Solar and Heliospheric Observatory coronagraph images. The event produced large fluxes of energetic particles up to energies >100 MeV at both Ulysses and the Earth. Enhancements of energetic particles were immediately observed at the Earth, with their onset times consistent with the velocity dispersion due to the streaming of particles along magnetic field lines from the location of particle acceleration in the corona to the Earth. To the contrary, at Ulysses, the energetic particles from the solar event were not detected until 4-11 hours later, and the increases of particle intensity were much more gradual. The onset times of particles in different energy channels were not organized by particle speed; rather they depended on both particle rigidity and speed, indicating that the transport of particles to Ulysses at high latitudes had a diffusive nature. The first-order anisotropy in the 40-90 MeV proton flux was significantly larger than what is expected from the Compton-Getting effect for many hours after the onset. The direction of the first-order anisotropy was not along the projection of local magnetic fields onto the scan plane of the detector and it was not affected by the polarity of the field either, indicating that the particles did not arrive at Ulysses through propagation along magnetic field lines and rather much of the anisotropy was produced by cross-field diffusion in the presence of a cross-field density gradient pointing toward the low latitude direction. All these observations are consistent with easy particles transport across the mean heliospheric magnetic fields. The apparent difficulty for the theory is that the observations require a cross-field diffusion that is too fast to be explained by random walk of field lines due only to supergranulation. Copyright 2003 by the American Geophysical Union. solar energetic particles, diffusion, interplanetary magnetic fields.
• Giacalone, J. (2002). The heliospheric magnetic field probed with fast charged particles. COSPAR Colloquia Series, 14(C), 217-223.
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  Abstract: We discuss the physics of the transport of energetic charged particles in the heliosphere. We put this in the context of using fast charged particles as probes of the heliospheric magnetic field. Since these particles move rapidly in the electromagnetic fields within space, they provide information about the global nature of the field itself. Although the magnetic field can be observed at a point in time and space using a magnetometer, the global field is not easily determined. This is where the information from energetic-particle observations, combined with analytic theory and modeling, can be valuable. © 2002 Elsevier B.V. All rights reserved.
• Giacalone, J., Jokipii, J. R., & Kóta, J. (2002). Particle acceleration in solar wind compression regions. Astrophysical Journal Letters, 573(2 I), 845-850.
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  Abstract: We present the results of a theoretical investigation of the acceleration of charged particles in regions of gradual solar wind compression. The mechanism we describe is similar to diffusive shock acceleration, except that it invokes a gradual compression of the plasma over many gyroradii rather than a shock. Recent observations of energetic particles associated with corotating interaction regions (CIRs) at 1 AU suggest that the particles were accelerated within the compression region between the fast and slow solar wind rather than at the associated forward and reverse shocks, which are at larger heliocentric distances. We show that nondiffusive effects such as magnetic mirroring are important in the inner heliosphere, particularly the injection of low-energy particles (e.g., pickup ions and suprathermal solar wind ions). We integrate the trajectories of an ensemble of test particles moving in synthesized electromagnetic fields, which are similar to what is currently known about corotating interaction regions in the inner heliosphere, prior to the formation of the forward and reverse shocks. We show that compression regions associated with CIRs at 1 AU with widths ∼0.03 AU can accelerate particles up to ∼10 MeV and produce energy spectra which are remarkably similar to recent observations.
• Giacalone, J. (2001). The Injection Problem. COSPAR Colloquia Series, 11(C), 377-385.
• Giacalone, J. (2001). The latitudinal transport of energetic particles associated with corotating interaction regions. Journal of Geophysical Research A: Space Physics, 106(A8), 15881-15887.
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  Abstract: We investigate the effect of large-scale magnetic turbulence in the solar wind on the transport of ∼1-10-MeV protons associated with corotating interaction regions (CIRs). We develop a quantitative model of the heliospheric magnetic field which is determined by the motions of magnetic foot points near the solar photosphere. The trajectories of many test particles are numerically integrated in this field to examine the variation of the particle distribution function with latitude. The foot points of the magnetic field lines, which extend radially from the source surface, execute a random walk in latitude and longitude. We find that the resulting long-wavelength magnetic fluctuations lead to significant latitudinal field line diffusion which simultaneously leads to significant latitudinal transport of CIR-associated energetic particles. The results from our model are qualitatively consistent with recent Ulysses observations of recurrent energetic particle intensity enhancements at high heliographic latitudes. Copyright 2001 by the American Geophysical Union.
• Giacalone, J., & Jokipii, J. R. (2001). The transport of energetic particles and cosmic rays in the heliosphere. Advances in Space Research, 27(3), 461-469.
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  Abstract: We discuss recent observations of energetic particles and cosmic rays lending insight into how these particles are influenced by the interplanetary magnetic field and what can be learned about the field itself by using the energetic particles as probes. Two recent observations on which we focus attention are those by Ulysses at high heliographic latitudes and those by the Advanced Composition Explorer of impulsive solar flare events. The Ulysses observations of low-rigidity energetic particles at high latitudes associated with corotating interaction regions at lower latitudes are consistent with propagation in a stochastic field superimposed on a Parker spiral. These observations indicate that the particles undergo a significant cross-field diffusion. More-recent observation of energetic particles from impulsive solar flare events show structure on a fine scale which seems also to reflect the field-line meandering. Large small-scale gradients normal to the local magnetic field are shown to be completely consistent with significant cross-field diffusion on larger time scales. © 2001 COSPAR. Published by Elsevier Science Ltd. All rights reserved.
• Giacalone, J., & Ellison, D. C. (2000). Three-dimensional numerical simulations of particle injection and acceleration at quasi-perpendicular shocks. Journal of Geophysical Research A: Space Physics, 105(A6), 12541-12556.
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  Abstract: We present results from three-dimensional numerical simulations of quasi-perpendicular collisionless shocks in order to determine whether cross-field diffusion, which is otherwise artificially suppressed in simulations which contain at least one ignorable spatial coordinate, is large enough to efficiently accelerate thermal particles and/or pickup ions. We find that although the simulated downstream distribution functions are quite steep, a fraction of the particles are accelerated to energies well above the thermal energy. This occurs only if the system contains fluctuations with wavelengths that are considerably larger than the gyroradii of the particles of interest (the high-energy ones). We find that this is due to the fact that the transport of the particles normal to the shock, against the downstream convection, is mostly influenced by the meandering of field lines on large scales. We also show that if the system does not contain these long-wavelength waves, the scattering is not sufficient to accelerate thermal particles or pickup ions. We use two different types of simulations to demonstrate this. In the first set of simulations we use the well-known hybrid simulation which treats the interaction between the particles and fields self-consistently. For computational tractability these simulations use very small spatial domains, and the effect of the large-scale field-line random walk is suppressed. However, this approximation accurately addresses the physics of the scattering at resonant wavelengths. Test-particle simulations, which are more computationally tractable than the hybrid simulations, are also performed for larger systems and to illustrate the effect of the long-wavelength waves. Copyright 2000 by the American Geophysical Union.
• Giacalone, J., Jokipii, J. R., & Mazur, J. E. (2000). Small-scale gradients and large-scale diffusion of charged particles in the heliospheric magnetic field. Astrophysical Journal Letters, 532(1 PART 2), L75-L78.
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  Abstract: We have carried out numerical simulations of the propagation of energetic charged particles in a turbulent magnetic field similar to that observed in the solar wind. If the particles are released impulsively near the Sun, in a region small compared with the field coherence scale (a solar flare, for example), they exhibit characteristic fluctuations in intensity at 1 AU (dropouts) associated with very steep localized gradients. These numerical simulations are quantitatively very similar to recent observations by the Advanced Composition Explorer spacecraft and are the result of the convection of alternatively filled and empty flux tubes past the spacecraft. These fluctuations occur naturally as part of the particle transport in the same field, which results in large-scale cross field diffusion and which has previously been used to study the propagation of corotating interaction region-associated particles to high heliographic latitudes.
• Mazur, J. E., Mason, G. M., Dwyer, J. R., Giacalone, J., Jokipii, J. R., & Stone, E. C. (2000). Interplanetary magnetic field line mixing deduced from impulsive solar flare particles. Astrophysical Journal Letters, 532(1 PART 2), L79-L82.
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  Abstract: We have studied fine-scale temporal variations in the arrival profiles of ∼20 keV nucleon-1 to ∼2 MeV nucleon-1 ions from impulsive solar flares using instrumentation on board the Advanced Composition Explorer spacecraft at 1 AU between 1997 November and 1999 July. The particle events often had short-timescale (∼3 hr) variations in their intensity that occurred simultaneously across all energies and were generally not in coincidence with any local magnetic field or plasma signature. These features appear to be caused by the convection of magnetic flux tubes past the observer that are alternately filled and devoid of flare ions even though they had a common flare source at the Sun. Thus, we have used the particles to study the mixing of the interplanetary magnetic field that is due to random walk. We deduce an average timescale of 3.2 hr for these features, which corresponds to a length of ∼0.03 AU.
• Scholer, M., Kucharek, H., & Giacalone, J. (2000). Cross-field diffusion of charged particles and the problem of ion injection and acceleration at quasi-perpendicular shocks. Journal of Geophysical Research A: Space Physics, 105(A8), 18285-18293.
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  Abstract: It is an open question how charged particles are injected at quasi-perpendicular shocks into a first-order Fermi acceleration mechanism. Cross-field diffusion of solar wind ions is a possible injection process. However, in a system with at least one ignorable spatial dimension, charged particles moving in fluctuating fields are tied to the magnetic field lines. We have therefore determined the cross-field diffusion coefficient of charged particles in self-consistently generated turbulence by three-dimensional hybrid simulations. The initial setup consists of a homogeneous magnetic field with an isotropic core plasma plus a second, nongyrotropic ion distribution. The combined distributions resemble the distribution found immediately downstream of the quasi-perpendicular Earth bow shock: Part of the solar wind is transmitted (core) and part is specularly reflected and subsequently convected downstream (nongyrotropic part). Such a particle distribution excites the Alfvén ion cyclotron and mirror mode instability. The turbulence scatters the nongyrotropic ions both parallel and perpendicular to the field. The perpendicular and the parallel diffusion coefficients have been determined for two values of the density of the nongyrotropic distributions, nb. The ratio of the two diffusion coefficients is smaller than the value predicted by hard sphere scattering theory, i.e., parallel scattering is considerably stronger than scattering perpendicular to the field. The power in the magnetic field fluctuations in the high nb case is comparable to the power obtained in a two-dimensional quasi-perpendicular shock simulation immediately behind the shock ramp. On the basis of perpendicular scattering time it is suggested that cross-field diffusion in the turbulent wave field generated by the specularly reflected ions is sufficient to inject and accelerate these ions efficiently at quasi-perpendicular shocks. Copyright 2000 by the American Geophysical Union.
• Giacalone, J. (1999). Particle transport and acceleration at corotating interaction regions. Advances in Space Research, 23(3), 581-590.
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  Abstract: The transport and acceleration of energetic nuclei associated with corotating interaction regions is discussed with emphasis on its importance relative to global heliospheric phenomena such as anomalous cosmic rays, the distant heliosphere, and propagation to high latitudes. We will discuss aspects of particle acceleration at the forward and reverse shocks bounding CIRs which support the idea that accelerated pickup ions are important contributors to energetic ions in the heliosphere. We will outline our current understanding of the source of CIR-associated energetic nuclei based on multi-spacecraft observations of the spatial variation of low-energy cosmic rays, as well as that of freshly ionized pickup ions. We will also discuss the propagation of CIR-associated energetic particles to high heliographic latitudes. We will present a model of the interplanetary magnetic field and show results from a numerical simulation which suggest that particles undergo significant latitudinal diffusion. ©1999 COSPAR. Published by Elsevier Science Ltd.
• Giacalone, J., & Jokipii, J. R. (1999). The transport of cosmic rays across a turbulent magnetic field. Astrophysical Journal Letters, 520(1 PART 1), 204-214.
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  Abstract: We present a new analysis of the transport of cosmic rays in a turbulent magnetic field that varies in all three spatial dimensions. The analysis utilizes a numerical simulation that integrates the trajectories of an ensemble of test particles from which we obtain diffusion coefficients based on the particle motions. We find that the diffusion coefficient parallel to the mean magnetic field is consistent with values deduced from quasi-linear theory, in agreement with earlier work. The more interesting and less understood transport perpendicular to the average magnetic field is found to be enhanced (above the classical scattering result) by the random walk, or braiding, of the magnetic field. The value of κ⊥ obtained is generally larger than the classical scattering value but smaller than the quasi-linear value. The computed values of κ⊥/κ∥, for a representation of the interplanetary magnetic field, are 0.02-0.04; these values are of the same general magnitude as those assumed in recent numerical simulations of cosmic-ray modulation and transport in the heliosphere, and give reasonable agreement with spacecraft observations of cosmic rays. Some consequences of these results for the interpretation of heliospheric observations are discussed.
• Giacalone, J. (1998). Cosmic-ray transport coefficients. Space Science Reviews, 83(1-2), 351-363.
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  Abstract: A review of cosmic-ray transport coefficients, based on historic and recent observations and theoretical insights, is presented. Particular emphasis is on the transport of cosmic rays across the magnetic field, which is of foremost importance, and is presently poorly understood and widely debated. © 1998 Kluwer Academic Publishers.
• Jokipii, J. R., & Giacalone, J. (1998). The theory of anomalous cosmic rays. Space Science Reviews, 83(1-2), 123-136.
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  Abstract: Anomalous cosmic rays are a heliospheric phenomenon in which interstellar neutral atoms stream into the heliosphere, are ionized by either solar radiation or the solar wind, and are subsequently accelerated to very high energies, greater than 1 GeV. Current thinking has the bulk of the acceleration to very-high energies taking place, by the mechanism of diffusive shock acceleration, at the termination shock of the solar wind. Detailed two-dimensional numerical simulations and models based on this picture show broad agreement with a number of the observed properties of anomalous cosmic rays. Recent improvements to this picture include the observation of multiply charged cosmic rays and the suggestion that some "preacceleration" of the initially ionized particles occurs in the inner heliosphere. © 1998 Kluwer Academic Publishers.
• Giacalone, J., & Jokipii, J. R. (1997). Spatial variation of accelerated pickup ions at co-rotating interaction regions. Geophysical Research Letters, 24(14), 1723-1726.
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  Abstract: The spatial distribution of accelerated particles at corotating interaction regions (CIR's) provides constraints on possible acceleration mechanisms. We point out some previously unrecognized aspects of acceleration at the forward and reverse shocks bounding CIRs, which support the idea that acceleration of pickup ions at these shocks is an important contributor to energetic ions in the inner heliosphere. We find that the acceleration of pickup ions is strongly favored at the reverse shock over the forward shock. Also, the scaling of the pickup-ion velocity distribution with respect to local solar wind speed is not necessarily useful within the CIR. Copyright 1997 by the American Geophysical Union.
• Giacalone, J., Burgess, D., Schwartz, S. J., Ellison, D. C., & Bennett, L. (1997). Injection and acceleration of thermal protons at quasi-parallel shocks: A hybrid simulation parameter survey. Journal of Geophysical Research A: Space Physics, 102(A9), 19789-19804.
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  Abstract: Collisionless shocks that propagate along the mean magnetic field are known to accelerate some fraction of the incident charged particles directly from the thermal pool to energies that are considerably higher than the energy at which the plasma rams into the shock. Using hybrid simulations, we address two issues: (1) the dependence of the injection/acceleration of thermal protons to energies much higher than the plasma ram energy on various shock parameters such as Mach number, plasma beta, etc., and (2) the effect of the high-energy particles, accelerated directly from the thermal population by the shock, on the macroscopic properties of the shock, most notably, on the density compression. We find that for supercritical Mach numbers the acceleration of the thermal plasma is efficient enough that the back pressure due to the energetic particles can significantly increase the density compression across the shock, above the value expected from the simple Rankine-Hugoniot prediction. Additionally, at low Alfvén Mach number,where the acceleration of the thermal plasma is inefficient, the density compression is smaller than the simple Rankine-Hugoniot prediction owing to the nonresonant fire hose instability. The acceleration efficiency increases with Mach number except at very high Alfvén Mach numbers, where it begins to decrease for Mach numbers greater than ∼ 10. This is due to the presence of a fixed, free-escape boundary that limits the size of the foreshock region measured in units of the mean-free paths of the accelerated particles. Additionally, we find that regardless of the upstream plasma parameters,the acceleration efficiency increases with both the density compression ratio across the shock and the distance to the free-escape boundary measured in units of the mean-free path of the energetic particles. Both of these are consistent with analytic theory and numerical models that use a phenomenological scattering law. Copyright 1997 by the American Geophysical Union.
• Giacalone, J., Jokipii, J. R., Decker, R. B., Krimigis, S. M., Scholer, M., & Kucharek, H. (1997). Preacceleration of anomalous cosmic rays in the inner heliosphere. Astrophysical Journal Letters, 486(1 PART I), 471-476.
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  Abstract: Because of the apparent difficulty in accelerating previously unaccelerated pickup ions locally at the solar wind termination shock, a model for anomalous cosmic-ray protons is considered in which the initial acceleration of pickup ions to ∼ 10-20 MeV occurs in the inner heliosphere. These accelerated pickup ions are assumed to be accelerated either by propagating interplanetary shocks or by some other, unspecified process. Voyager 2 Low-Energy Charged Particle (LECP) observations at low energies are used to normalize their spectra. The ions are then transported to the termination shock, where they are further accelerated to anomalous cosmic-ray energies. We use a well-established transport model to simulate this process. In this model, the two-dimensional cosmic-ray transport equation is solved using the assumed (and normalized) source of energetic particles (∼0.01-20 MeV) located at 10 AU. We show that the computed spectra at higher energies (≳100 MeV) are consistent with observed anomalous cosmic-ray fluxes and suggest that interplanetary shocks, especially those in the inner heliosphere, may play an important role in the initial acceleration of pickup ions leading to anomalous cosmic rays. © 1997. The American Astronomical Society. All rights reserved.
• Jokipii, J. R., & Giacalone, J. (1996). The acceleration of pickup ions. Space Science Reviews, 78(1-2), 137-148.
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  Abstract: The well-established association of pickup ions with anomalous cosmic rays shows that acceleration of pickup ions to energies above 1 GeV occurs. At present, diffusive shock acceleration of the pickup ions at the termination shock of the solar wind seems to be the best candidate for acceleration to the high energies of anomalous cosmic rays, accounting well for many of their observed properties. However, it is shown that acceleration of pickup ions from their initial energies by this process appears to be difficult at very strong, nearly perpendicular shocks such as the termination shock. This "injection" problem remains without a clear solution. A number of alternatives have been proposed for the initial acceleration of pickup ions to the point where diffusive acceleration at the termination shock can take over, but none of these processes has yet emerged as a clear favorite. © 1996 Kluwer Academic Publishers.
• Giacalone, J., & Jokipii, J. R. (1995). Simulations of pickup-ion acceleration at quasi-perpendicular shocks. Space Science Reviews, 72(1-2), 441-446.
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  Abstract: We present results from hybrid simulations (kinetic ion/fluid electron) of the interaction of interstellar pickup ions with collisionless shocks. Since cross-field transport is unphysically suppressed in the one-dimensional geometry used here, an ad hoc scattering algorithm is used to model this effect. This is a necessary step to accelerate the pickup ions from their initial low energies at quasi-perpendicular shocks to the high energies which are often observed associated with traveling interplanetary shocks by Ulysses. © 1995 Kluwer Academic Publishers.
• Giacalone, J. (1994). Cross-field diffusion of ions in one- and two-dimensional hybrid simulations of collisionless shocks. Geophysical Research Letters, 21(22), 2441-2444.
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  Abstract: It can be demonstrated analytically that under certain geometries used in numerical simulations of collisionless shocks in which there is at least one ignorable spatial coordinate, the transport of particles across the magnetic field is essentially zero. This notion is tested using one- and two-dimensional hybrid simulations (kinetic ions/ fluid electrons). We find, as the theorem predicts, the particles treated kinetically are tied to the same field line on which they start.
• Giacalone, J., & Jokipii, J. R. (1994). Charged-particle motion in multidimensional magnetic-field turbulence. Astrophysical Journal Letters, 430(2 PART 2), L137-L140.
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  Abstract: We present a new analysis of the fundamental physics of charged-particle motion in a turbulent magnetic field using a numerical simulation. The magnetic field fluctuations are taken to be static and to have a power spectrum which is Kolmogorov. The charged particles are treated as test particles. It is shown that when the field turbulence is independent of one coordinate (i.e., k lies in a plane), the motion of these particles across the magnetic field is essentially zero, as required by theory. Consequently, the only motion across the average magnetic field direction that is allowed is that due to field-line random walk. On the other hand, when a fully three-dimensional realization of the turbulence is considered, the particles readily cross the field. Transport coefficients both along and across the ambient magnetic field are computed. This scheme provides a direct computation of the Fokker-Planck coefficients based on the motions of individual particles, and allows for comparison with analytic theory.
• Giacalone, J., Burgess, D., Schwartz, S. J., & Ellison, D. C. (1993). Ion injection and acceleration at parallel shocks: Comparisons of self-consistent plasma simulations with existing theories. Astrophysical Journal Letters, 402(2), 550-559.
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  Abstract: We present a simulation study of particle acceleration by parallel collisionless shocks and compare our results with existing shock acceleration theories, in particular, diffusive and shock drift acceleration. We extend the earlier work in this field by drawing attention to the similarities and discrepancies between the results obtained from the more realistic, self-consistent simulations and these well-established theories. We have simulated several shocks of different Alfvén Mach number which propagate into a medium containing magnetic fluctuations, some of which are initially superposed on the background field, and some of which are generated self-consistently by energetic ions streaming ahead of the shock. Although the simulated characteristics of the energetic ions are in general agreement with the shock acceleration theories, we have found some surprising results. For example, the parallel shock, at times, exhibits features similar to that expected at more perpendicular shocks, although, on average the features are consistent with Fermi acceleration predictions (as expected at a parallel shock). Also, quasi-linear theory, which assumes that the magnetic fluctuations about the mean field are small in amplitude, agrees quite well with the simulation results, where the fluctuations are on the order of ΔB/B ∼ 1.

Proceedings Publications

• Esman, T., Espley, J., Gruesbeck, J., Fowler, C., Xu, S., Elrod, M., Harada, Y., Giacalone, J., Halford, A., & Verbiscer, A. (2023, may). Martian Ionospheric Magnetic Fluctuations. In EGU General Assembly Conference Abstracts.
• Goodrich, K. A., Wilson, I., Schwartz, S., Cohen, I. J., Turner, D. L., Whittlesey, P., Caspi, A., Rose, R., Smith, K., Allen, R., Burgess, D., Caprioli, D., Cassak, P., Eastwood, J., Giacalone, J., Gingell, I., Haggerty, C., Halekas, J., Hospodarsky, G., , Howes, G., et al. (2023, jul). Multi-point Assessment of the Kinematics of Shocks (MAKOS): A Heliophysics Mission Concept Study. In Bulletin of the American Astronomical Society, 55.
• Guo, F., Antiochos, S., Cassak, P., Chen, B., Chen, X., Dong, C., Downs, C., Giacalone, J., Haggerty, C., Ji, H., Karpen, J., Klimchuk, J., Li, W., Li, X., Oka, M., Reeves, K., Swisdak, M., & Tu, W. (2023, jul). Advancing Theory and Modeling Efforts in Heliophysics. In Bulletin of the American Astronomical Society, 55.
• Christian, E., Cohen, C., Cummings, A., Davis, A., Desai, M., De, N. G., Giacalone, J., Hill, M., Joyce, C., Labrador, A., Leske, R., Matthaeus, W., McComas, D., McNutt Jr., ., Mewaldt, R., Mitchell, D., Mitchell, J., Rankin, J., Roelof, E., , Schwadron, N., et al. (2022, mar). New Data from the IS??IS instrument Suite on Parker Solar Probe. In 37th International Cosmic Ray Conference.
• Cohen, C., Christian, E., Cummings, A., Davis, A., Desai, M., Nolfo, G. d., Giacalone, J., Hill, M., Joyce, C., Labrador, A., Leske, R., Matthaeus, W., McComas, D., Mewaldt, R., Mitchell, D., Mitchell, J., Rankin, J., Roelof, E., Schwadron, N., , Stone, E., et al. (2022, mar). Parker Solar Probe's Measurements of the 29 November 2020 Solar Energetic Particle Event. In 37th International Cosmic Ray Conference.
• Cohen, C., Mason, G. M., Jin, M., Nitta, N., Christian, E., Cummings, A., Desai, M., De, N. G., Giacalone, J., Hill, M., Joyce, C., Labrador, A., Leske, R., Matthaeus, W., McComas, D., McNutt, R., Mewaldt, R., Mitchell, D., Mitchell, J. G., , Rankin, J., et al. (2022, jul). Multi-spacecraft Observations of Heavy Ion Characteristics in the 28 October 2021 Solar Energetic Particle Event. In 44th COSPAR Scientific Assembly. Held 16-24 July, 44.
• Cohen, C., mason, G., Jin, M., Nitta, N., Christian, E., Cummings, A., Desai, M., De, N. G., Giacalone, J., Hill, M., Joyce, C., Labrador, A., Leske, R., Matthaeus, W., McComas, D., McNutt, R., Mewaldt, R., Mitchell, D., Mitchell, J., , Rankin, J., et al. (2022, oct). Heavy Ion Characteristics Observed by Multiple Spacecraft Observations in the 28 October 2021 Solar Energetic Particle Event. In The Third Triennial Earth-Sun Summit (TESS, 54.
• David, L., Fraschetti, F., Giacalone, J., Wimmer-Schweingruber, R. .., Berger, L., & Lario, D. (2022, mar). Energy Balance at Interplanetary Shocks: In-situ Measurement of the Fraction in Supra-thermal and Energetic Ions with ACE and Wind. In 37th International Cosmic Ray Conference.
• Fraschetti, F., Katsuda, S., Sato, T., Giacalone, J., & Jokipii, J. (2022, mar). Unfolding of the vortical amplification of the magnetic field at inward shocks of Supernova remnant Cassiopeia A. In 37th International Cosmic Ray Conference.
• Getachew, T., McComas, D., Joyce, C., Palmerio, E., Christian, E., Cohen, C., Desai, M., Giacalone, J., Hill, M., Matthaeus, W., McNutt, R., Mitchell, D., Mitchell, G., Rankin, J., Roelof, E., Schwadron, N., Szalay, J., Zank, G., Zhao, L., , Lynch, B., et al. (2022, oct). PSP/IS\ensuremath{\Theta}IS Observation of a Solar Energetic Particle Event Associated with a Streamer Blowout Coronal Mass Ejection during Encounter 6. In The Third Triennial Earth-Sun Summit (TESS, 54.
• Gkioulidou, M., Gkioulidou, M., Opher, M., Kornbleuth, M., Dialynas, K., Giacalone, J., Richardson, J., Zank, G., Fuselier, S., Mitchell, D., Krimigis, S., Roussos, E., & Baliukin, I. (2022, jul). On the energization of pickup ions downstream of the heliosheric termination shock, by comparing 0.52-55 keV observed ENA spectra to simulated ENAs inferred by proton hybrid simulations.. In 44th COSPAR Scientific Assembly. Held 16-24 July, 44.
• Guo, F., Li, X., Kong, X., Chen, B., Shen, C., Glesener, L., & Giacalone, J. (2022, oct). Confronting Current and Future Imaging Spectroscopic Observations with Integrated Multiphysics Models. In The Third Triennial Earth-Sun Summit (TESS, 54.
• Guo, F., Lo, M., Zhao, L., Giacalone, J., & Lario, D. (2022, oct). The Effect of Large-scale Turbulence on Energetic Particle Profiles across Interplanetary Shocks. In The Third Triennial Earth-Sun Summit (TESS, 54.
• Leske, R., Christian, E., Cohen, C., Cummings, A., Davis, A., Desai, M., De, N. G., Giacalone, J., Hill, M., Joyce, C., Labrador, A., Matthaeus, W., McComas, D., McNutt, R., Mewaldt, R., Mitchell, D., Mitchell, J. G., Rankin, J., Roelof, E., , Schwadron, N., et al. (2022, jul). Parker Solar Probe Observations of Near-Sun 3He-rich Solar Energetic Particle Events. In 44th COSPAR Scientific Assembly. Held 16-24 July, 44.
• Mitchell, J. G., De, N. G., Hill, M., Christian, E., Leske, R., Richardson, I. G., McComas, D., Wiedenbeck, M., Cohen, C., Giacalone, J., Labrador, A., McNutt, R., Mewaldt, R., Mitchell, D., Schwadron, N., Bale, S., Joyce, C., Niehof, J., & Szalay, J. (2022, jul). The First 3 Years of ISOIS Energetic Electron Measurements. In 44th COSPAR Scientific Assembly. Held 16-24 July, 44.
• Guo, F., Kong, X., Li, X., Shen, C., Chen, B., Daughton, W., Li, H., & Giacalone, J. (2021, jun). The roles of magnetic reconnection and flare termination shock in accelerating particles in solar flares. In American Astronomical Society Meeting Abstracts, 53.
• Nikoukar, R., Richardson, J., Roelof, E., Opher, M., Krimigis, S., Hamilton, D. C., Hill, M., Florinski, V., Decker, R., Kota, J., Giacalone, J., Dialynas, K., & Brown, L. (2021, jan). Energy Dependence of GCR Anisotropies in the VLISM. In 43rd COSPAR Scientific Assembly. Held 28 January - 4 February, 43.
• Trotta, D., Franci, L., Burgess, D., Hellinger, P., & Giacalone, J. (2020, may). The role of turbulence strength on the acceleration of transrelativistic electrons. In EGU General Assembly Conference Abstracts.
• De, N. G., Bruno, A., Ryan, J., Dalla, S., Giacalone, J., Richardson, I., & Christian, E. (2019, Jul). Long Duration Gamma-ray Flares and High Energy Solar Energetic Particles: Is there a Connection?. In 36th International Cosmic Ray Conference (ICRC2019), 36.
• Giacalone, J. (2019, Jan). Particle Acceleration at Shocks Moving Through Turbulent Plasmas. In APS Division of Plasma Physics Meeting Abstracts, 2019.
• Nolfo, G. A., Bruno, A., Ryan, J., Dalla, S., Giacalone, J., Richardson, I., Christian, E., Stochaj, S., Bazilevskaya, G., Boezio, M., Martucci, M., Mikhailov, V., & Munini, R. (2019, May). Comparing Long-Duration Gamma-Ray Flares and High-Energy Solar Energetic Particles. In Solar Heliospheric and INterplanetary Environment (SHINE 2019).
• Christian, E., Nolfo, G., Bruno, A., Boezio, M., Christian, E., Dalla, S., Giacalone, J., Martucci, M., Merg{\`e}, M., Munini, R., & Ricci, M. (2018, jul). Comparing Long Duration Gamma-ray Flares and High Energy Solar Energetic Particles; no. In Solar Heliospheric and INterplanetary Environment (SHINE 2018).
• Giacalone, J. (2018, jul). Energetic Particle Transport and Acceleration at Interplanetary Shocks. In 42nd COSPAR Scientific Assembly, 42.
• Lario, D., Berger, L., Wilson, L., Decker, R., Haggerty, D., Roelof, E., Wimmer-Schweingruber, R., & Giacalone, J. (2018, oct). Flat Proton Spectra in Large Solar Energetic Particle Events. In Journal of Physics Conference Series, 1100.
• Giacalone, J. (2017, sep). The Acceleration of Thermal Ions at a Strong, Quasi-Parallel Interplanetary Shock: A Hybrid Simulation. In Journal of Physics Conference Series, 900.
• {Cohen}, C., {Giacalone}, J., {Wiedenbeck}, M., , G. (2015, apr). "{Examining Particle Transport in Multi-Spacecraft $^{3}$He-Rich SEP Events}". In AAS/AGU Triennial Earth-Sun Summit, 1.
• Giacalone, J., & Jokipii JR, . (2012, Fall). Suprathermal Ions Associated with Strong Interplanetary Shocks. In AIP Conf. Proc, 1436, 130.
• Giacalone, J., Guo, F., & Giacalone, J. (2012, Fall). The acceleration of electrons at perpendicular shocks and its implication for solar energetic particle events. In AIP Conf. Proc, 1500, 93.
• Zank, G., Borovsky, J., Bruno, R., Cirtain, J., Cranmer, S., Elliott, H., Giacalone, J., Gonzalez, W., Li, G., Marsch, E., Moebius, E., Pogorelov, N., Spann, J., & Verkhoglyadova, O. (2012, Fall). SOLAR WIND 13: Proceedings of the Thirteenth International Solar Wind Conference. In SOLAR WIND 13: Proceedings of the Thirteenth International Solar Wind Conference, 1539.

Poster Presentations

• Christian, E., McComas, D., Cummings, A., Desai, M., Giacalone, J., Hill, M., Krimigis, S., Livi, S., Matthaeus, W., McNutt, R., Mewaldt, D., Roelof, E., Schwardron, N., Stone, E., von, R. T., & Wiedenbeck, M. E. (2013, Spring). Integrated Science Investigation of the Sun (ISIS) on Solar Probe Plus. American Geophysical Union, Spring Meeting.
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  Abstract: #SH41A-07
• Giacalone, J. (2013, February). The Heliosphere after Voyager and IBEX. High Altitude Observatory Colloquium Series.
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  Date: 02/20
• Giacalone, J. (2013, March). Theoretical Aspects of Solar Energetic Particle Acceleration and Transport. The First Solar Probe Plus Workshop. Pasadena, CA.
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  Date: 03/27
• Giacalone, J. (2012, April). Particle Acceleration at Astrophysicsl Shocks: Are Self-Excited Magnetic Fluctuations Important?. American Physical Society April Meeting. Atlanta, GA.
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  Date: 04/01
• Giacalone, J. (2012, December). Physical Processes that Disperse Solar Energetic Particles in Space and Their Relation to Multi-Point Measurements. Fall AGU. San Francisco.
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  Date: 12/04
• Giacalone, J. (2012, Fall). The Physics of Particle Acceleration From Thermal to Suprathermal Energies at Collisionless Shocks. American Geophysical Union, Fall Meeting.
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  Abstract: #SH32B-05
• Giacalone, J. (2012, June). Particle Acceleration at CIRs: A Theoretical Perspective. 2012 SHINE Workshop. Maui, HI.
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  Date: 06/26
• Giacalone, J. (2012, March). An Analysis of Solar-Energetic Particle Events Associated with Strong Interplanetary Shocks. 11th Astrophysics Conference on Space Weather and the Space Radiation Environment. Palm Springs, CA.
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  Date: 03/02
• Giacalone, J., Jokipii, J., & Kota, J. (2012, July). Cosmic Rays During the Most-Recent Sunspot Minimum. 39th COSPAR Scientific Assembly. Mysore, India.
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  Abstract: D3.1-22-12
• Guo, F., & Giacalone, J. (2012, Fall). The Acceleration of Electrons at Collisionless Shocks in the Existence of Large-scale Magnetic Fluctuations. American Geophysical Union, Fall Meeting.
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  Abstract: #SH33F-02
• Jokipii, J., Kota, J., & Giacalone, J. (2012, July). Constraints on the Origin of Anomalous Cosmic Rays. 39th COSPAR Scientific Assembly. Mysore, India.
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  Abstract: E1.18-12-12

Others

• Opher, M., Richardson, J., Giacalone, J., Kornbleuth, M., Brandt, P., Provornikova, E., Gkioulidou, M., Sok{\'o\l}, J., Buxner, S., Nikoukar, R., Holst, B., Gross, N., Swisdak, M., Dialynas, K., Dayeh, M. A., Zieger, B., Onubogo, C., Bair, E., Miller, J., , Reisenfeld, D., et al. (2023). Our Heliospheric Shield, a Case of a Habitable Astrosphere: Need to Revisit this region with In-Situ Measurements with Modern Instrumentation.