1/20/2017 - Oblique Whistler-Mode Waves in the Earth's Inner Magnetosphere

Information:

3:30 PM - 4:30 PM
Geology 6704

Presented By:
Oleksiy Agapitov - UCB

Abstract

Oblique Whistler-Mode Waves in the Earth's Inner Magnetosphere

The recent spacecraft observations of oblique whistler-mode waves in the Earth inner magnetosphere, as well as the various consequences of the presence of such waves for electron scattering and acceleration, are presented. The statistics of occurrences and intensity of oblique chorus waves in the region of the outer radiation belt, comprised between the plasmapause and geostationary orbit is performed. On this basis, we demonstrate that varying amounts of oblique waves can significantly change the rates of particle scattering, acceleration, and precipitation into the atmosphere during quiet times as well as in the course of a storm. The significant parallel electric field component provides the favorable conditions for nonlinear wave-particles interactions processes and recent spacecraft measurements allowed to study the effects for the radiation belts particles. Huge numbers of different nonlinear structures (double layers, electron holes, non-linear whistlers, etc. referred to as Time Domain Structures - TDS) have been observed by the electric field experiment on board the Van Allen Probes and THEMIS. A large part of the observed non-linear structures are associated with whistler waves and some of them can be directly driven by whistlers. Observations of electron velocity distributions and chorus waves by the Van Allen Probes provided long-lasting signatures of electron Landau resonant interactions with oblique chorus waves in the outer radiation belt. In the inhomogeneous geomagnetic field, such resonant interactions then lead to the formation of a plateau in the parallel (with respect to the geomagnetic field) velocity distribution due to trapping of electrons into the wave effective potential. The feedback from trapped particles provides steepening of the parallel electric field and development of TDS seeded from initial the whistler structure (well explained in terms of Particle-In-Cell model). We demonstrate that oblique whistler-mode chorus waves can be considered as an important ingredient of the radiation belt system and can continuously play a key role in many aspects of wave-particle resonant interactions.

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