Multi-Point Observations of Modulated Whistler-Mode Waves and Energetic Electron Precipitation

In this study, we present simultaneous multi-point observations of whistler-mode waves detected by RBSP-B, associated with conjugate electron precipitation observed through enhanced BARREL X-rays at L ∼ 6 from noon to dusk. Both long period modulation at periods of several to tens of minutes and short period modulation at about tens of seconds are observed in X-ray measurements. Similar periodicities are also observed for whistler-mode wave amplitude. We show that the correlation coefficient between whistler-mode waves and electron precipitation is high in several regions, including plumes and plasma trough. Ultra-low-frequency waves (8-30 mHz), which have been suggested to play a potential role in precipitating electrons by modulating whistler-mode wave intensity or loss cone size, show a weak correlation with whistler-mode wave amplitudes and the X-ray counts during the conjunction. We further evaluate whistler-mode wave driven electron precipitation using a physics-based technique. The time evolution of the modeled electron precipitation is found to be remarkably consistent with the modulation in the BARREL X-ray counts both in plumes and plasma trough. By taking advantage of the high-resolution wave data and close conjunction, we provide strong evidence that whistler-mode waves are not only directly responsible for the longer modulation (several to tens of minutes), but also the shorter modulation (tens of seconds) of the electron precipitation.