Modeling Ring Current Ion Anisotropy and Plasma Instability in Non-Dipolar Magnetic Fields

Details Modeling Ring Current Ion Anisotropy and Plasma Instability in Non-Dipolar Magnetic Fields Modeling Ring Current Ion Anisotropy and Plasma Instability in Non-Dipolar Magnetic Fields

Dec 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsm24a..05j&link_type=abstract

American Geophysical Union, Fall Meeting 2010, abstract #SM24A-05

Physics

[2753] Magnetospheric Physics / Numerical Modeling, [2772] Magnetospheric Physics / Plasma Waves And Instabilities, [2778] Magnetospheric Physics / Ring Current, [2788] Magnetospheric Physics / Magnetic Storms And Substorms

Scientific paper

Intense plasma waves, which may cause significant acceleration or loss of energetic particles, are excited in the inner magnetosphere during magnetically active periods. The free energy for these waves is supplied from the anisotropic ring current ion and electron distributions. We evaluate the spatial and temporal development of the ring current during several high-speed streams driven geomagnetic storms, using our newly improved kinetic model (RAM) which has been extended for non-dipolar magnetic field geometry. The RAM is two-way coupled with a 3-D equilibrium code that calculates self-consistently the magnetic field (SCB) in force balance with the anisotropic ring current distributions. The plasma boundary conditions of RAM-SCB are specified from LANL data measured at geosynchronous orbit. We investigate the effects of non-dipolar magnetic field configuration on ring current evolution like the formation of ion ring distributions due to energy dependent drifts, charge exchange losses, and injection boundaries between open and closed drift paths. We find that as strong depressions in the self-consistent magnetic field develop on the nightside during the main phase of a storm, the particles’ gradient-curvature drift velocity increases, the ion fluxes are reduced and the ring current is confined close to Earth. As a result of drift-shell splitting, the pitch angle anisotropy decreases at large L shells on the nightside and increases on the dayside. We calculate the linear growth rate of EMIC and magnetosonic waves in the equatorial plane and identify regions for potential excitation of these plasma instabilities in the inner magnetosphere during storm time.

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