Physics
Scientific paper
Apr 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003jgra..108.1143s&link_type=abstract
Journal of Geophysical Research (Space Physics), Volume 108, Issue A4, pp. SMP 2-1, CiteID 1143, DOI 10.1029/2002JA009489
Physics
130
Magnetospheric Physics: Energetic Particles, Precipitating, Magnetospheric Physics: Plasma Waves And Instabilities, Ionosphere: Plasma Waves And Instabilities, Magnetospheric Physics: Magnetosphere-Inner
Scientific paper
During magnetic storms, relativistic electrons execute nearly circular orbits about the Earth and traverse a spatially confined zone within the duskside plasmapause where electromagnetic ion cyclotron (EMIC) waves are preferentially excited. We examine the mechanism of electron pitch-angle diffusion by gyroresonant interaction with EMIC waves as a cause of relativistic electron precipitation loss from the outer radiation belt. Detailed calculations are carried out of electron cyclotron resonant pitch-angle diffusion coefficients Dαα for EMIC waves in a multi-ion (H+, He+, O+) plasma. A simple functional form for Dαα is used, based on quasi-linear theory that is valid for parallel-propagating, small-amplitude electromagnetic waves of general spectral density. For typical observed EMIC wave amplitudes (1-10nT), the rates of resonant pitch-angle diffusion are close to the limit of ``strong'' diffusion, leading to intense electron precipitation. In order for gyroresonance to take place, electrons must possess a minimum kinetic energy Emin which depends on the value of the ratio (electron plasma frequency/electron gyrofrequency); Emin also depends on the properties of the EMIC wave spectrum and the ion composition. Geophysically interesting scattering, with Emin comparable to 1 MeV, can only occur in regions where (electron plasma frequency/electron gyrofrequency) >=10, which typically occurs within the duskside plasmapause. Under such conditions, electrons with energy >=1 MeV can be removed from the outer radiation belt by EMIC wave scattering during a magnetic storm over a time-scale of several hours to a day.
Mansergh Thorne Richard
Summers Danny
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