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
sensor in the BBR survey data at 30 second temporal resolution. Most of
the QP episodes occurred in a frequency range between 1- 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 3-5.
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.