Observations and Modeling of Low-Energy Ring Current Particles in the Dawn Sector of the Inner Magnetosphere During Geomagnetic Storms

Details Observations and Modeling of Low-Energy Ring Current Particles in the Dawn Sector of the Inner Magnetosphere During Geomagnetic Storms Observations and Modeling of Low-Energy Ring Current Particles in the Dawn Sector of the Inner Magnetosphere During Geomagnetic Storms

May 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agusmsm23c..03b&link_type=abstract

American Geophysical Union, Spring Meeting 2005, abstract #SM23C-03

Mathematics

Logic

2712 Electric Fields (2411), 2716 Energetic Particles, Precipitating, 2730 Magnetosphere: Inner, 2764 Plasma Sheet

Scientific paper

Four Defense Meteorological Satellite Program (DMSP) satellites detected fluxes of low-energy ions precipitating well equatorward of auroral electrons in the dawn/morning magnetic local time sector during the magnetic storm of October 29-31, 2003. Ion precipitation weakened and vanished after recover began. A survey of the DMSP database reveals that near-dawn ion precipitation is a main-phase characteristic of all large magnetic storms. The CRRES satellite observed similar ion signatures near the magnetospheric equator during the magnetic storm of March 24, 1991. To explain the observations, we calculated drift paths of test-particles in the equatorial plane in the inner magnetosphere using a modified Volland-Stern electric field model. We allowed the driving electric field and the shielding parameter to vary in time, as indicated by the March 1991 storm dynamics. In all cases we follow the drift trajectories of ions and electrons with selected values of magnetic moment μ above, equal to and below μc, where μc is defined as the critical magnetic moment for which the westward gradient-curvature drift exactly matches its eastward corotation drift. The main difference between the storm's dynamic and lull stages is that ions with 0 < μ < μc penetrate inside the zero-energy Alfvén boundary (ZEAB). Furthermore, low-energy ions with μ ~ μc drift to the dawn sector inside the ZEAB. To reconcile DMSP and CRRES observations with allowed ion drift paths, the data suggest two source populations for near-dawn ion precipitation. The lowest-energy ions were initially energized in the evening local-time sector of the plasmasphere and subsequently co-rotated eastward. Higher-energy ions with μ < μc originated in the plasma sheet and drifted close to the Earth under the combined influences of time-varying electric fields and azimuthal gradients in the Earth's magnetic field generated by the stormtime ring current. After the electric field was shielded from the inner magnetosphere the newly injected ions also co-rotated into the dawn sector. Ion precipitation in the dawn sector results from a combination of pitch-angle scattering by ambient waves and by the dictates of drift paths that carry ions to very low L-shells.

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