Simultaneous space and ground‐based observations of a plasmaspheric virtual resonance

Abstract

We present simultaneous space and ground‐based observations of Pi2 pulsations which occurred during a substorm on 25 September 2014. The timeline for this event starts at ∼06:04 UT when the THEMIS probe D located inside the plasmasphere detected Pi2 pulsations in the electric and magnetic fields. Cross‐spectral analysis shows the azimuthal electric field and compressional magnetic field oscillated nearly in quadrature, highly suggestive of a standing fast‐mode wave. Simultaneous Pi2 observations from dayside and nightside ground magnetometers at low latitudes indicate a global wave mode. A latitudinal magnetometer chain on the nightside observed a phase reversal in the H component of the Pi2 pulsations when crossing the footprint of the plasmapause, estimated from THEMIS spacecraft measurements. Spectral analysis of data from ground magnetometers in this latitudinal chain showed fundamental and second harmonic spectral peaks in their H and D components. Similar pulsation signatures at comparable harmonic frequencies were observed by three midlatitude SuperDARN HF radars, both poleward and equatorward of the plasmapause ionospheric footprint. Finally, the longitudinal polarization pattern and azimuthal phase propagation of midlatitude Pi2 pulsations are consistent with previous observations of a plasmaspheric virtual resonance being excited by a longitudinally localized source near midnight.

Nightside Pi2 Wave Properties During an Extended Period With Stable Plasmapause Location and Variable Geomagnetic Activity

“…The frequencies and amplitudes of Pi2 waves such as PVR are strongly affected by the plasmapause location. The present study extends previous work relating Pi2 wave activity to plasmapause location (e.g., Ghamry et al, ; Shi et al, ; Takahashi et al, , ) by examining wave activity during an extended interval with stable plasmapause location and variable geomagnetic activity. The following items summarize our key findings: Multiple‐satellite passes and PTP simulations indicate that the plasmapause location is stable for at least 2 h over a wide range of MLT.…”

“…PVR can also have finite wave amplitudes both inside and outside the plasmasphere (Lee & Kim, 1999). Observational studies have confirmed the existence of PVR, and they have frequencies in the Pi2 range (Ghamry et al, 2015;Luo et al, 2011;Nosé, 2010;Shi et al, 2017;Takahashi et al, 2009;Teramoto et al, 2011); they may also be classified as Pc4 waves (e.g., Takahashi et al, 2005).…”

Review of the accomplishments of mid-latitude Super Dual Auroral Radar Network (SuperDARN) HF radars

“…The authors concluded that the observed wave was a cavity mode resonance which had been stimulated by compressional waves which had propagated duskward from the source region in the midnight sector. Shi et al (2017) provided a careful and thorough analysis of multiple data sets from THEMIS, ground magnetometer, and FHE, FHW, and BKS. Shi et al (2017) attempted here to separate a plasmaspheric virtual resonance (PVR) where wave energy is primarily confined to the plasmasphere but a small portion escapes beyond the plasmapause, from a plasmaspheric cavity resonance (PCR) where wave energy should be confined to the plasmasphere.…”

“…Shi et al (2017) provided a careful and thorough analysis of multiple data sets from THEMIS, ground magnetometer, and FHE, FHW, and BKS. Shi et al (2017) attempted here to separate a plasmaspheric virtual resonance (PVR) where wave energy is primarily confined to the plasmasphere but a small portion escapes beyond the plasmapause, from a plasmaspheric cavity resonance (PCR) where wave energy should be confined to the plasmasphere. The radar data are key as they provide high spatial resolution across the plasmapause as shown in Fig.…”

“…The radar data are key as they provide high spatial resolution across the plasmapause as shown in Fig. 34 from Shi et al (2017), where the wave phase and power are taken across a number of range gates of data from FHE. The peak in power occurs at 60.6°N which is just inside the estimated position of the plasmapause at 60.9°N, while a minimum in power occurs at 59.60°N.…”