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

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.