Property of low-energy plasma associated with chorus wave modulation

Abstract:

Recent studies have shown that chorus is the wave mode that is responsible for precipitation of energetic electrons which subsequently drive the pulsating aurora. Intensity modulation of chorus is often correlated with modulation of the low-energy plasma density based on spacecraft potential observations. Such density modulations could be an important factor for modulating the growth rate of chorus. However, it has been difficult to directly measure such plasma populations or to determine their properties due to satellite charging effects and the limited energy ranges of particle detectors. We used THEMIS data to directly find low-energy plasma in correlation with chorus modulations. Events were selected where satellite charging is modest, intense and quasi-periodic chorus modulations exist, and the satellites were located in the nightside equatorial region. We found 27 such events, and 24 of those showed low-energy electron fluxes modulation in correlation with chorus intensity. Those electrons are separated from photoelectrons of satellite origin and are present even after correcting for spacecraft potential changes. Those electrons are seen for both short (~10 sec) and long (~minutes) period chorus modulations, and also for both spacecraft potential increase and decrease events. We will further discuss the properties of those low-energy plasma and influences on chorus wave growth.