Magnetic field line curvature induced pitch angle diffusion in the radiation belts

Details Magnetic field line curvature induced pitch angle diffusion in the radiation belts Magnetic field line curvature induced pitch angle diffusion in the radiation belts

Dec 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufmsm41a1131y&link_type=abstract

American Geophysical Union, Fall Meeting 2004, abstract #SM41A-1131

Physics

2716 Energetic Particles, Precipitating, 2720 Energetic Particles, Trapped, 2730 Magnetosphere: Inner

Scientific paper

Magnetic field line curvature (FLC) affects particle populations throughout the magnetosphere. Strongly curved field lines quickly isotropize particle distributions with relatively low energies in the tail and keep the loss cone well supplied. In the inner magnetosphere, weaker curvature allows higher energy particles to remain trapped for longer periods of time, but limits on lifetimes are still imposed. Because of the exponential nature of the onset of non-adiabaticity (leading to pitch angle scattering), rough estimates for the importance of this mechanism assume an ``on/off'' switch. If ǎrepsilon is above threshold, the particles are quickly scattered, while populations with ǎrepsilon below this value are not affected at all. Here ǎrepsilon is the ratio between the maximum gyroradius a particle on a particular field line may have and that field line's minimum radius of curvature. We investigate the effects of magnetic field line curvature in the inner magnetosphere using the pitch angle diffusion equation for phase space density with the diffusion coefficient based on an empirically derived FLC induced pitch angle scattering model. A range of numerically calculated results shows the effects of varying not only ǎrepsilon, but various magnetic field parameters. Using these results in conjunction with magnetic field parameters calculated from a combination of the Tsygenenko 2001 and IGRF magnetic field models we explore the effects of both Dst and the dipole tilt angle on different particle populations. We show results that support the ``on/off'' model with threshold values of ǎrepsilon varying between 0.15 and 0.38. Higher speed populations do not require as large of values of ǎrepsilon to diffuse at the same rate as lower speed populations.

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