Plasma Wave-Driven Energetic Electron Precipitation: Wave-Particle Interactions Affecting the Polar Atmosphere (Invited)

Abstract:

Wave particle interactions are a fundamental physical mechanism driving change in the radiation belts. Growing evidence indicates that cyclotron resonance between plasma waves and energetic electrons play crucial roles for the acceleration of electrons to relativistic energies. It has long been recognised that the same resonances also pitch-angle scatter electrons, moving them towards the loss cone and loss into the atmosphere through precipitation. ULF, ELF and VLF plasma waves have all been shown to have an important role to play in precipitation of energetic electrons into the mesosphere. VLF Whistler-mode waves precipitate energetic electrons through "normal" cyclotron resonance, while ULF EMIC waves can precipitate relativistic electrons through "anomalous" cyclotron resonance.

We combine observations from multiple sources to show how wave activity controls the loss of radiation belt particles, determining both the loss rate and the atmospheric location for which this loss occurs. In particular we will use VLF wave observations made in LEO by the DEMETER spacecraft to contextualise electron precipitation observations provided by the POES spacecraft in LEO as well as the AARDDVARK network of ground-based sensors. These results provide evidence that strong diffusion due to high wave intensities dominates during storm-times, producing rapid pitch angle scattering and hence immediate precipitation. Our suggestion is confirmed by the completely independent observations of atmospheric HOx distributions, produced in the polar atmosphere by electron precipitation. This presentation combines observations made in space with ground-based measurements, emphasising their importance in this research.

This work demonstrates how the changing intensity of plasma waves can decrease polar ozone concentrations in the mesosphere. Such decreases have also recently been experimentally observed during particle precipitation events. There is growing evidence that this is important route by which plasma waves can alter the chemistry of the polar atmosphere and lead to polar surface climate variability.