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.