Physics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsm41b2019d&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #SM41B-2019
Physics
[2720] Magnetospheric Physics / Energetic Particles: Trapped, [2730] Magnetospheric Physics / Magnetosphere: Inner, [2752] Magnetospheric Physics / Mhd Waves And Instabilities, [2774] Magnetospheric Physics / Radiation Belts
Scientific paper
We examine the process of outer radiation belt energization and magnetopause loss driven by ultra low frequency (ULF) waves during geomagnetic storms. We consider energization arising through the adiabatic transport of electrons into regions of higher magnetic field strength, via drift-resonant interactions with the ULF waves. A useful way to view this process is by the mapping of phase space density (PSD) along electron drift-trajectories according to Liouville's theorem. In this context, the impact of ULF wave activity is arguably most significant when the resulting transport links un-trapped and trapped electron drift trajectories, in which case it is important to ask where the un-trapped trajectories originate. For example, electron trajectories originating in the night-side plasmasheet provide an enhancement in PSD at lower L-shell. On the other hand, electron trajectories intersecting the magnetopause enable the transport of an absence of phase space density or "PSD hole", leading to a radiation belt PSD depletion. The location of the last closed drift shell in relation to the magnetopause and regions of ULF wave activity therefore plays a pivotal role in determining whether ULF wave driven transport enhances or depletes electron phase space density. This is demonstrated using a numerical model for ideal MHD waves within a magnetosphere including day/night asymmetry and a parabolic magnetopause to drive the adiabatic transport of equatorially mirroring electrons. The electron transport model also includes a simple convection electric field model, a PSD plasmasheet source and magnetopause loss. Narrow band ULF waves are launched from the dayside magnetopause and are found to most significantly perturb electron trajectories in the afternoon sector. Parametrically scanning the convection electric field (Ec), we find that ULF wave driven transport results in a rapid PSD depletion for low values of Ec and a significant PSD enhancement for high values of Ec, depending on the ULF wave amplitude, and the location of the separatrix between trapped and untrapped electrons (controlled by Ec) in the afternoon sector where the ULF wave interaction is strongest.
Degeling A. W.
Rankin Robert
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