Multi-Instrument Characterisation of Magnetospheric Cold Plasma Dynamics in the 22 June 2015 Geomagnetic Storm

Abstract

We present a comparison of magnetospheric plasma mass/electron density observations during an 11-day interval which includes the geomagnetic storm of 22 June 2015. For this study we used: equatorial plasma mass density derived from geomagnetic field line resonances (FLRs) detected by Van Allen Probes and at the ground-based magnetometer networks EMMA and CARISMA; in situ electron density inferred by the Neural-network-based Upper hybrid Resonance Determination algorithm applied to plasma wave Van Allen Probes measurements. The combined observations at L ˜4, MLT ˜16 of the two longitudinallyseparated magnetometer networks show a temporal pattern very similar to that of the in situ observations: a density decrease by an order of magnitude about 1 day after the Dst minimum, a partial recovery a few hours later, and a new strong decrease soon after. The observations are consistent with the position of the measurement points with respect to the plasmasphere boundary as derived by a plasmapause test particle simulation. A comparison between plasma mass densities derived from ground and in situ FLR observations during favourable conjunctions shows a good agreement. We find however, for L < ˜3, the spacecraft measurements to be higher than the corresponding ground observations with increasing deviation with decreasing L, which might be related to the rapid outbound spacecraft motion in that region. A statistical analysis of the average ion mass using simultaneous spacecraft measurements of mass and electron density indicates values close to 1 amu in plasmasphere and higher values (˜2-3 amu) in plasmatrough.

A Statistical Study of Modulation of Electromagnetic Ion Cyclotron Waves Observed on Ground

“…It is because at a higher L‐shell the length of the field line is longer, which gives rise to longer time period of oscillation. Therefore, the Eigen frequency of the field line oscillation increases as we move toward lower L‐shells (Anderson et al., 1989; Vellante et al., 2021). The long period modulation is also found to be present in the EMIC waves observed on the ground; however, it is not as frequent as short period modulation.…”

“…This feature of field line oscillation was confirmed by various studies. According to satellite studies (Anderson et al, 1989;Vellante et al, 2021), the Eigen frequency of the field line oscillation increases as we move toward lower L-shells; in other words, the time period of oscillation decreases. It is in agreement with the tendency of having lower values of τ s for higher peak frequency.…”