Other
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufmsm53b1292z&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #SM53B-1292
Other
2114 Energetic Particles (7514), 2720 Energetic Particles: Trapped, 2760 Plasma Convection (2463), 2774 Radiation Belts
Scientific paper
Diffusive compress acceleration of energetic charged particle is similar to diffusive shock acceleration. The particle acceleration occurs through either drift acceleration or Fermi process. 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. Particles are accelerated whenever the plasma with its embedded magnetic fields is compressed. This is a first-order particle acceleration mechanism. Shock is just an extreme profile of compression, but particle acceleration does not have to have a shock present. In this acceleration theory, diffusion is only needed to keep the particles near the acceleration site long enough to get the particles to much higher energies than their initial energies. Inside the magnetosphere, a shock is unlikely, but plasma compression still occurs. 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 compression acceleration occurs ~6-12 Re on the night-side and there particles can double their energies in matter of a few minutes. The acceleration 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. Energetic electrons accelerated at near- Earth tail will drift to the dawn side and emit whistler waves or other electron-related waves, and energetic ions will drift to dusk side and emit ion cyclotron waves and form partial ring current there. When magnetospheric convection is enhanced, particularly during a fast sunward flow in the tail, the acceleration becomes stronger and particle acceleration site gets closer to the Earth. These could change the radiation belt content and disrupt the magnetospheric current system.
Qin Gan
Zhang Minghui
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