Quasi‐Periodic Whistler Mode Emission in the Plasmasphere as Observed by the DSX Spacecraft

Abstract

We describe the quasi‐periodic (QP) whistler‐mode emissions found in the plasmasphere as detected by electric and magnetic instrumentation onboard the Demonstration and Science Experiments (DSX) spacecraft in medium Earth orbit. Over the course of the nearly 2‐year mission, at least 45 episodes of whistler mode QP emissions were detected by the Broad Band Receiver (BBR) onboard DSX. Episodes of QP emissions were identified by discrete events having a clear unambiguous periodic nature as detected by both the electric antennae and search coil magnetic sensors in the BBR survey data at 30 s temporal resolution. Most of the QP episodes occurred in a frequency range between 1 and 4 kHz, in a band previously identified by Van Allen Probes and Cluster investigators. However, episodes were also detected by DSX at higher frequencies ‐ events in these episodes extending all the way to 15 kHz. We present our findings on these unusual high frequency events in the presentation herein. Specifically, these high frequency QP episodes tended to be observed near dawn/dusk when the spacecraft was at relatively high magnetic latitudes and on magnetic L‐shells between 3 and 5. Another unusual feature of these episodes is that individual up‐drifting events making up the episode were found to sometimes occur concurrently in time: The high frequency portion of one up‐drifting “polliwog‐shaped” event overlapped in time with the low frequency portion of the subsequent event. This behavior of the QP emissions has not been previously emphasized and we consider how this temporal concurrence relates to the source processes.

Overview of the Demonstration and Science Experiments (DSX) Mission

“…Another unusual type of whistler mode emission observed by DSX included episodes with individual "up-drifting" (increasing in frequency) events overlapping each other in time. Results are described in Farrell et al (2022). The first ACE experiments in July 2019 collected data for system identification of the spacecraft's flexible-body dynamics.…”

Quasiperiodic Emissions: Fine Structure Corresponding to a Bouncing Wave

“…These waves are typically referred to as quasiperiodic (QP) emissions. They predominantly occur at frequencies between about 0.5 and 4 kHz (Hayosh et al., 2014), but can extend up to frequencies as high as 15 kHz (Farrell et al., 2022). While ground‐based (Morrison et al., 1994) and low‐altitude spacecraft (Hayosh et al., 2014) surveys indicate that QP emissions are primarily dayside phenomenon, satellite observations at larger radial distances reveal the emissions at essentially all local times, with a slightly larger occurrence on the duskside (Němec et al., 2018).…”

On the fine inner structure of whistler mode quasiperiodic emissions

“…Although the existence of QP emissions is known already for decades (Carson et al, 1965), they are still not fully understood. The event frequencies may be also at times significantly higher, up to 15 kHz (Farrell et al, 2022).…”