Physics
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufmsm41c..01z&link_type=abstract
American Geophysical Union, Fall Meeting 2006, abstract #SM41C-01
Physics
2720 Energetic Particles: Trapped, 2740 Magnetospheric Configuration And Dynamics, 2760 Plasma Convection (2463), 2774 Radiation Belts
Scientific paper
When a gas is compressed, its temperature increases and particles in the gas are accelerated. Particle acceleration at collision shock waves acts on the same mechanism although the compression at the shock is very abrupt and particles need to depend on spatial diffusion to achieve energies more than 4 times their original energy. This is a first-order particle acceleration process and it is much more effective than the second-order energy diffusion in many space plasma environments. Based on the adiabatic theory of particle motion and the frozen-in-law of space plasma, we can write the rate of particle energy increase and particle pitch-angle change in terms of the divergence of plasma flow. It shows that particles are accelerated whenever the plasma with its embedded magnetic fields is compressed. If compression is in direction perpendicular to the magnetic field, particle pitch-angle gets larger and the particle distribution becomes more pancake-like. Inside the magnetosphere, a shock is unlikely, but plasma compression can still occur. This perhaps is driving particle acceleration during magnetic storm periods, but it should also occur during quiet times at lower rate. Using a model map of magnetospheric convection pattern, we found that the compression of magnetospheric plasma can play important roles in particle acceleration and trapping. It is a large-scale phenomenon. The strongest compressional acceleration occurs ~6-12 Re on the night-side plasma sheet. It has a correlation with the speed of external solar wind that drives the magnetospheric convection and the location of plasmapause that indicates the level of magnetospheric convection. In this paper, we are going to show how particle acceleration initiates and how the particle flux increases propagate through the magnetosphere during an enhancement of magnetospheric convection of magnetic storm. We will also discuss to role of particle diffusion in the acceleration process.
Qin Gan
Zhang Minghui
Zhu Yaming
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