Whistler Mode Chorus Waves and Their Influence on Diffuse Electron Aurora and Ionospheric Conductance.

Abstract:

Ionospheric conductance acts as an essential linkage of the magnetosphere – ionosphere – thermosphere coupling. Strong ionospheric conductance heats the ionosphere – thermosphere system, initiating a new circulation pattern in the thermosphere and producing ion and electron outflows that subsequently modify magnetospheric dynamics. Aurora precipitation is the second major energy source after solar irradiation that ionizes the Earth’s upper atmosphere. Among various aurora types, diffuse electron aurora takes over 60% of auroral precipitation and therefore strongly contributes to the ionospheric conductance. Diffuse electron aurora occurs when the inner magnetospheric electrons are scattered into a loss cone due to the wave – particle interaction. Upper-Band Chorus (UBC) waves, Lower-Band chorus (LBC) waves, and Electron Cyclotron Harmonics (ECH) waves are known as the main contributors to diffuse electron aurora. However, there has been no comprehensive study that calculates diffuse electron precipitation directly from the inner magnetospheric wave activities. Additionally, although the UBC, LBC, and ECH waves produce different energy spectrum of precipitating electrons, their individual impact on ionospheric conductance hasn’t been fully understood. This presentation calculates global maps of diffuse electron aurora and ionospheric conductance directly derived from the inner magnetospheric waves, specifically the UBC and LBC waves. From the THEMIS observations, we obtain the chorus wave statistics and the wave-time magnetospheric plasma conditions during quiet, moderate, and disturbed geomagnetic activities. Then, we used a quasi-linear theory to calculate wave-driven diffuse electron precipitation, and a physics-based, empirical model of electron impact ionization to estimate the wave-driven ionospheric conductance. Finally, our physics-based results are compared to the well-known empirical models of aurora precipitation and ionospheric conductance. The model-data comparison shows that LBC waves contribute to the strong aurora precipitation and high Pederson conductance observed in the dawn sector.