Relationship of the Van Allen radiation belts to solar wind drivers |
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| Institution: | 1. Physics and Astronomy Department, Dartmouth College, Hanover, NH 03755, USA;2. Space Sciences Applications Laboratory, The Aerospace Corporation, Los Angeles, CA, USA;1. Osservatorio Astronomico di Capodimonte, Istituto Nazionale di Astrofisica, Napoli, Italy;2. Department of Physics “E. Pancini”, University of Naples “Federico II”, Napoli, Italy;3. John Hopkins University Applied Physical Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723, USA;1. Center for Mathematics and Computer Science (CWI), Amsterdam, The Netherlands;2. T-5 Applied Mathematics and Plasma Physics, Los Alamos National Laboratory, 87545 Los Alamos, NM, USA;3. CCS-7 Applied Computer Science, Los Alamos National Laboratory, 87545 Los Alamos, NM, USA;1. GSI Helmholtz Center for Heavy Ion Research, Biophysics Department, Darmstadt, Germany;2. Technical University of Darmstadt, Institute of Condensed Matter Physics, Darmstadt, Germany;1. Institute of Radio Physics and Electronics, University of Calcutta, Kolkata 700009, India;2. Narula Institute of Technology, Kolkata 700109, India;1. Geophysical Institute, Slovak Academy of Sciences, Dúbravská cesta 9, 845 28 Bratislava, Slovak Republic;2. Geomagnetic Observatory, Geophysical Institute, Slovak Academy of Sciences, Komárňanská 108, 947 01 Hurbanovo, Slovak Republic;3. Institute of Geophysics, Academy of Sciences of the Czech Republic, Bo?ní II/1401, 141 31 Prague 4, Czech Republic |
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| Abstract: | Discovery of the Van Allen radiation belts by instrumentation flown on Explorer 1 in 1958 was the first major discovery of the Space Age. A view of the belts as distinct inner and outer zones of energetic particles with different sources was modified by observations made during the Cycle 22 maximum in solar activity in 1989–1991, the first approaching the activity level of the International Geophysical Year of 1957–1958. The dynamic variability of outer zone electrons was measured by the NASA–Air Force Combined Radiation Release and Effects Satellite launched in July 1990. This variability is caused by distinct types of heliospheric structure which vary with the solar cycle. The largest fluxes averaged over a solar rotation occur during the declining phase from solar maximum, when high-speed streams and co-rotating interaction regions (CIRs) dominate the inner heliosphere, leading to recurrent storms. Intense episodic events driven by high-speed interplanetary shocks launched by coronal mass ejections (CMEs) prevail around solar maximum when CMEs occur most frequently. Only about half of moderate storms, defined by intensity of the ring current, lead to an overall flux increase, emphasizing the need to quantify loss as well as source processes; both increase when the magnetosphere is strongly driven. Three distinct types of acceleration are described in this review: prompt and diffusive radial transport, which increases energy while conserving the first invariant, and local acceleration by waves, which change the first invariant. The latter also produce pitch angle diffusion and loss, as does outward radial transport, especially when the magnetosphere is compressed. The effect of a dynamic magnetosphere boundary on radiation belt electrons is described in the context of MHD-test particle simulations driven by measured solar wind input. |
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