Substorm Driven Chorus Waves: Decay Timescales and Implications for Pulsating Aurora

Abstract

Energetic electron precipitation (EEP) associated with pulsating aurora can transfer greater than 30 keV electrons from the outer radiation belt region into the upper atmosphere and can deplete atmospheric ozone via collisions that produce NOx and HOx molecules. Our knowledge of exactly how EEP occurs is incomplete. Previous studies have shown that pitch angle scattering between electrons and lower-band chorus waves can cause pulsating aurora associated with EEP and that substorms play an important role. In this work, we quantify the timescale of chorus wave decay following substorms and compare that to previously determined timescales. We find that the chorus decay e-folding time varies based on magnetic local time (MLT), magnetic latitude, and wave frequency. The fastest decay occurs for lower-band chorus in the 21 to 9 MLT region and compares well to the timescale of Troyer et al. (2022) for energetic pulsating aurora. We are able to further support this connection by modelling our findings in a quasi-linear diffusion simulation. These results provide observations of how chorus waves behave after substorms and add additional statistical evidence linking energetic pulsating aurora to substorm driven lower-band chorus waves.