Ionospheric radar measurements of waves with equatorward phase propagation generated by energetic particles (Invited)

Abstract:

Energetic particles injected from the magnetotail into the Earth's inner magnetosphere will experience gradient-curvature drift and thus move around the Earth, constituting part of the global ring current. Such drifting particles can drive MHD wave modes through wave-particle interactions, leading to perturbations in the electric and magnetic fields in the magnetosphere and ionosphere.

Such particle-driven waves generally have a small azimuthal scale length, and this results in a strong attenuation of the wave between the ionosphere and the ground, making ionospheric radars particularly useful instruments for their study. In addition, a subset of such waves have a strong equatorward phase propagation (a small scale length in latitude), which results in further attenuation. Such events have been observed by a variety of radar systems over the last 20 years at L-shells ranging from 5 - 15. The latitude of the observations has previously been determined to have a strong influence on the driving particle energies, and hence the wave characteristics. Here we report on recent progress in our understanding of such waves, made possible through the combination of the SuperDARN radar array and substorm morphology provided through IMAGE observations of the global UV aurora. It is revealed that the proximity of the wave observations and the substorm also has a strong influence on particle energy and wave characteristics. In-situ particle data from the van Allen probes has provided an opportunity to directly measure the driving particles for the lower latitude wave observations.