Ground Based and Van Allen Probes Observations of Cold Plasma Redistribution Associated with Nightside Reconnection and Substorm Injection
Abstract:
Plasmasphere erosion carries cold dense plasma of ionospheric origin toward the noontime cusp and dayside magnetopause. The ionospheric footprint of this process is seen as a continuous plume of storm enhanced density (SED) extending from the dusk sector into and through the daytime cusp region and back across polar latitudes in a polar cap tongue of ionization (TOI). This circulation brings high density plasmaspheric material to the reconnection sites at the magnetopause and in the tail with associated impact on reconnection rates. The March 17th 2013 storm provides quantitative evidence at multiple points within this redistribution chain that significant plasma fluxes are involved both at ionospheric and magnetospheric altitudes.We use Van Allen Probes data, ground-based radar, and DMSP observations to track these fluxes from the dusk sector plasmapause to the dayside cusp and across polar latitudes to the midnight sector. Foster et al. (GRL, 2014) reported a pronounced increase in polar cap TEC magnitude beginning at the onset of the March 17th storm and continuing sporadically until the time of a substorm onset at ~ 22 UT. Antisunward flow in the TOI carried the eroded material onto auroral field lines involved in midnight sector reconnection and substorm particle energization.
Both RBSP-A and RBSP-B observed patchy cold plasma density enhancements at apogee (~ 6 Re) on field lines mapping down to the region where TOI plasma was observed to exit the polar cap. Electron density was determined both from EMFISIS plasma wave observations and from EFW probe potentials. The patches of high altitude TOI material show enhanced cold plasma densities of 20 to 40 cm-3. Both spacecraft were immersed in the cold plasma enhancement until the onset of the magnetic field depolarization and particle injection event. The Van Allen Probes data are the first reported observations of TOI plasma near the apex of nightside auroral field lines. The long duration of the TOI fluxes suggests that the midnight sector region associated with magnetotail reconnection and substorm injection was richly populated with cold dayside plasmaspheric material during the March 17, 2013 event.