[IGPP Everyone] TODAY - EPSS Space Physics seminar announcement - Friday October 22, 2021 - 03:30 PM Pacific Time (US and Canada)

[Sowmendran, Margie (IGPP)]

R E M I N D E R - T O D A Y

SPACE PHYSICS SEMINAR

DEPARTMENT OF EARTH, PLANETARY, AND SPACE SCIENCES
DEPARTMENT OF ATMOSPHERIC AND OCEANIC SCIENCES
UNIVERSITY OF CALIFORNIA, LOS ANGELES

ZOOM LINK PROVIDED BELOW

 https://ucla.zoom.us/j/92101918782?pwd=Z2o5RmI4OEpBWW4zcG1DZStIUWgrZz09

The generation of two-band chorus waves in the Earth's outer radiation belt

Jinxing Li
Department of Earth, Planetary, and Space Sciences
University of California Los Angeles

Abstract

Whistler-mode chorus waves typically occurs in two distinct frequency bands separated by a gap. The origin of this two-band structure remains a long-standing question. Fundamental questions include: 1) Are chorus spectral gaps formed near the equatorial source region or during propagation away from the equator? 2) How is the two-band structure formed? 3) Why are chorus spectral gaps typically located just below 0.5 fce (fce: electron-gyrofrequency)? By analyzing Van Allen Probes data, we show that chorus spectral gaps are observed in the source region where chorus waves propagate both in the parallel and anti-parallel directions to the magnetic field. Observations show that banded chorus waves are commonly accompanied by two separate anisotropic electron components. We explain that initially generated chorus waves quickly isotropize the electron distribution through Landau resonant acceleration. The altered electron distribution, after returning to the magnetic equator, exhibits two anisotropic populations which lead to the generation of two-band chorus waves. The Landau resonant velocities are close to 0.5 vAe (vAe: electron Alfven velocity), which increase as latitude. Consequently, Landau resonances at high latitudes lead to electron isotropization above 0.5 vAe and wave spectral gaps formation below 0.5 fce at equator. Using 1D and 2D PIC simulations, we demonstrate that the initially excited single-band chorus waves alter the electron distribution immediately via Landau resonance, and suppresses the electron anisotropy at medium energies. This naturally divides the electron anisotropy into a low and a high energy components, and lead to the formation of two-band chorus waves.


Friday, October 22, 2021
3:30 - 5:00 PM

In-Charge:  Marco Velli

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