Space Plasma Seminar: Recent Observational Insights Into Magnetosphere-Ionosphere Coupling Within The Plasmaspheric Boundary Layer
Philip J. Erickson, MIT Haystack Observatory
Tuesday, May 7, 2013, 3:30pm
In the terrestrial geospace system, boundary layers develop at the interfaces where plasma populations with different thermal and compositional properties overlap. Over the last three decades, renewed research efforts have focused on the sub-auroral Plasmasphere Boundary Layer (PBL) equatorward of the high latitude electron precipitation boundary. Here, the relatively cold, dense plasma in the inner plasmasphere encounters the hot, tenuous plasmas characteristic of the outer plasmasphere. Electromagnetic coupling within the PBL links its dynamics to active, strong Region 2 ring current electric fields driven by asymmetric plasma pressure gradients concentrated in the dusk to midnight sectors. The resulting coupling processes produce a wealth of interesting and inherently non-local phenomena, including storm enhanced density gradients, plasmaspheric plumes, sub-auroral polarization streams, and narrow intense sub-auroral ion drifts. Complex feedback mechanisms couple both micro- and macro-scale ionospheric conductivity gradients to driving Region 2 electric fields, with energy flow likely occurring both to and from the magnetosphere.
The recent launch of the twin Van Allen Probes radiation belt probe spacecraft is providing an unprecedented opportunity to examine the dynamics of these phenomena. These platforms are equipped with a full set of wave and particle instruments for both electron and ion species, and the spacecraft transit the PBL three times daily on their way to and from apogee. Frequently, these PBL passes are magnetically connected to locations within the fields of view of ground-based distributed instrumentation which regularly produce both wide-field and regional detailed observations of key ionospheric and plasmasphere parameters. In particular, the greatly expanded mid-latitude SuperDARN HF radar network provides a multi-hour snapshot in magnetic local time of ionospheric convection parameters, at temporal cadences of minutes. Global GPS-based total electron content in both vertical and slant directions gives indications of ionospheric and plasmaspheric electron density content. The sub-auroral Millstone Hill UHF ionospheric radar system provides wide field, fine scale, full altitude profiles of plasma temperature, density, composition, and velocity. Taken as a whole, the combined ground-based and satellite data sets allow a unique simultaneous examination of conditions in the plasmasphere, magnetosphere, and ionosphere, advancing knowledge on the relative importance of sources and sinks within magnetosphere-ionosphere coupling processes.
The seminar will first present an overview of important PBL phenomena. The remainder of the talk will describe recent exciting observational results illuminating key inner magnetosphere processes, using coordinated SuperDARN and Millstone Hill wide field experiments during Van Allen Probes spacecraft conjunction intervals.