Effects of a geomagnetic pulsation on electron precipitation spectra

Kavanagh, A., Honary, F. and Senior, A.

Lancaster University, Lancaster, UK

Electrons with energies in excess of 30 keV form a potential source population for relativistic electrons in the outer radiation belt. One loss mechanism of these sub-relativistic electrons from the magnetosphere is precipitation linked to substorm activity, whether directly or following gradient-curvature drift of the freshly injected electron population. This can be observed using cosmic noise absorption measurements from a riometer. The precipitation is caused by the scattering of electrons into the loss cone by VLF whistler-mode waves; however, the precipitation can itself be modulated on timescales of seconds to tens of minutes. Using EISCAT data we investigate the change in energy spectra within a Pc5 pulsation (260 seconds) to determine the effect on the different levels of particle energy. The Coroniti-Kennel theory of ULF wave-electron interaction predicts a change in the shape of the high energy tail; alternatively, a shift in the whole spectrum would indicate that the pulsation in the precipitation is caused by acceleration in a parallel electric field such as that caused by kinetic Alfven wave.