EMFISIS Survey and Burst Mode Observations of Chorus Properties in the Context of the Chorus-to-Hiss Mechanism
Abstract
Whistler-mode chorus waves and plasmaspheric hiss play key roles in driving both particle acceleration and losses in the Earth's magnetosphere. Here, Van Allen Probes EMFISIS observations are coupled with ray tracing simulations to determine the fraction of chorus wave power that occurs with the initial conditions required to access the plasmasphere and subsequently evolve into plasmaspheric hiss. Statistical maps of the angular distribution of chorus wave power are presented using both survey mode data, which is based on a single 0.5s waveform captured every 6s, and continuous burst mode data, which is sampled at 35kHz continuously for 6s. High-resolution burst mode data allows us to resolve individual chorus elements, including rising and falling tone structures, and to take strides towards accounting for short-timescale variations in the wave vector angle. Using data captured in both modes we conclude that for most chorus source locations, only an extremely small fraction of power occurs with the wave vector orientation required to propagate into the plasmasphere. The exception to this is when the chorus source is located close to the edge of a plasmaspheric plume. In this region, strong azimuthal density gradients modify the wave propagation trajectories such that large fractions, up to 96%, of chorus wave power can gain access to the plasmasphere. This result demonstrates that the region of the magnetosphere close to plasmaspheric plume structures provides an important access region for chorus waves to enter the plasmasphere. However, chorus wave power is typically weaker in the region where plumes are frequently observed, and the properties of chorus in this region have not been directly evaluated. As such, we propose to directly study the wave properties and propagation characteristics of chorus that occurs in this important region of the magnetosphere, close to plasmaspheric plumes.
- Publication:
-
43rd COSPAR Scientific Assembly. Held 28 January - 4 February
- Pub Date:
- January 2021
- Bibcode:
- 2021cosp...43E1159H