Pitch angle diffusion of low‐energy electrons by whistler mode waves

It has often been argued that electrons with energy below approximately 10 keV cannot be pitch‐angle diffused by whistler mode waves because they have less than a critical minimum parallel energy. We show that there is no theoretical justification for an energy threshold based on the grounds of either resonance or instability and present energy/pitch angle plots from the low energy plasma analyzer (LEPA) on the CRRES spacecraft which support this analysis because they have features to be expected from a whistler mode interaction. This shows that whistler mode diffusion is responsible for a substantial amount of low‐energy electron precipitation at high latitudes and is probably responsible for the diffuse aurora. Furthermore, we show that releasing lithium from the CRRES spacecraft in the outer zone was unlikely to stimulate precipitation or to trigger a substorm.