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 longitudinally-separated 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.