Physics
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmsm54b..04n&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #SM54B-04
Physics
[2704] Magnetospheric Physics / Auroral Phenomena, [2730] Magnetospheric Physics / Magnetosphere: Inner
Scientific paper
The diffuse aurora constitutes one of the most important loss processes of plasma sheet electrons, supplying the majority of ionizing energy input into the high-latitude region during conditions of both low and high solar wind driving. It is generally agreed that wave-particle interactions, including scattering losses by electrostatic electron cyclotron harmonic (ECH) waves and electromagnetic whistler-mode chorus waves, play an essential role in the occurrence of the diffuse aurora. However, the precise role of each wave mode has remained a source of controversy for many years. To quantify the scattering effects of these two wave modes, we have improved the methodology for computation of quasi-linear diffusion coefficients and adopted statistical wave models based on the survey of ECH waves and chorus using the entire CRRES database. Our results demonstrate that, whistler-mode chorus is the dominant mechanism for loss of injected plasma sheet electrons from the inner magnetosphere (4 < L < 7) over the midnight-to-dawn (0000-0600) MLT sector. Observed chorus waves cause rapid pitch angle scattering, on timescales of a few hours, for plasma sheet electrons from hundreds of eV to tens of keV over a broad range of pitch angle up to ~80 deg. Such scattering is responsible for diffuse auroral precipitation and the formation of “pancake” pitch angle distributions. In contrast, ECH waves can only induce efficient precipitation loss of electrons below ~ 100 eV but have little scattering influence on plasma sheet electrons > 1 keV, suggesting rather minor contributions from ECH waves to the diffuse auroral precipitation. Our results also show that the scattering effects on plasma sheet electrons by the waves are strongly dependent on the level of geomagnetic activity.
Chen Leon L.
Horne Richard B.
Mansergh Thorne Richard
Meredith Nigel P.
Ni Binbin
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