Contribution of Kinetic Alfven Waves to Energetic Electron Precipitation From the Plasma Sheet During a Substorm

Energetic (greater than or similar to 50 keV) electron precipitation from the magnetosphere to the ionosphere during substorms can be important for magnetosphere-ionosphere coupling. Using conjugate observations between the THEMIS, ELFIN, and DMSP spacecraft during a substorm, we have analyzed the energetic electron precipitation, the magnetospheric injection, and the associated plasma waves to examine the role of waves in pitch-angle scattering plasma sheet electrons into the loss cone. During the substorm expansion phase, ELFIN-A observed 50-300 keV electron precipitation from the plasma sheet that was likely driven by wave-particle interactions. The identification of the low-altitude extent of the plasma sheet from ELFIN is aided by DMSP global auroral images. Combining quasi-linear theory, numerical test particle simulations, and equatorial THEMIS measurements of particles and fields, we have evaluated the relative importance of kinetic Alfven waves (KAWs) and whistler-mode waves in driving the observed precipitation. We find that the KAW-driven bounce-averaged pitch-angle diffusion coefficients D-alpha 0 alpha 0 near the edge of the loss cone are similar to 10(-6)-10(-5) s(-1) for these energetic electrons. The D-alpha 0 alpha 0 due to parallel whistler-mode waves, observed at THEMIS similar to 10-min after the ELFIN observations, are similar to 10(-8)-10(-6) s(-1). Thus, at least in this case, the observed KAWs dominate over the observed whistler-mode waves in the scattering and precipitation of energetic plasma sheet electrons during the substorm injection.

Automated summary

Energetic electron precipitation from the magnetosphere to the ionosphere during substorms is important for magnetosphere-ionosphere coupling. Through observations and analysis, it was found that wave-particle interactions are likely responsible for the precipitation of energetic electrons from the plasma sheet. Kinetic Alfven waves were found to dominate over whistler-mode waves in scattering and precipitating energetic plasma sheet electrons during the substorm injection.