Quasi‐Periodic Whistler Mode Emission in the Plasmasphere as Observed by the DSX Spacecraft. Issue 8 (5th August 2022)

• Record Type: Journal Article
• Authors: Farrell, W. M.; Lauben, D. S.; Miller, J. A.; Inan, U. S.; Linscott, I. R.; Galkin, I.; Su, Y.‐J.; Johnston, W. R.; Starks, M. J.; Sanchez, J. C.; Ginet, G.
• Is Part Of: Journal of geophysical research. Volume 127:Issue 8(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-08-05
• Subjects: quasi‐periodic -- whistler mode -- plasmasphere -- plasma waves; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1029/2022JA030327
• Languages: English
• ISSNs: 2169-9380

Abstract

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. Plain Language Summary: During its nearly 2‐year mission, the Demonstration and Science Experiments (DSX) spacecraft detected a number of episodes of medium‐altered radio emissions known as "quasi‐periodic (QP)" emissions. We show that these emissions are consistent with propagation in the plasma medium in the "whistler mode"—an allowable mode in the plasma medium. In the past, the emission has been described as periodic signal intensifications or drifting bursts typically found between 0.2 and 5 kHz, with the burst periodicity ranging from 10s of seconds to 10s of minutes. We report herein on the DSX observation of a set of QP episodes that extend to frequencies as high as 15 kHz. We also focus our study on QP episodes where the individual bursts appear to overlap in time. This latter characteristic may indicate a source emission region modulated by periodic plasma density waves in the outer plasmasphere. Key Points: We find quasi‐periodic (QP) episodes that extend to high frequencies near 15 kHz and have drifting emissions that overlap in time The QP emissions having burst overlap points to a possible source modulation by density waves in the plasmasphere The measurement set is from a broadband receiver onboard the USAF/Demonstration and Science Experiments spacecraft in medium Earth orbit