2011 SuperDARN Workshop
Midlatitude Ionospheric Features in the Plasmasphere Boundary Layer: The View From Millstone Hill
Atmospheric Sciences Group, MIT Haystack Observatory, MA, USA
abstract. For over 5 decades, the Millstone Hill UHF large aperture radar system, located in Westford, MA, has made extensive measurements of the mid-latitude / sub-auroral ionosphere as a NSF supported Upper Atmosphere Facility, using the powerful technique of incoherent scatter radar (ISR). The measurements allow direct E, F and topside region ionospheric profiles of electron density, electron and ion temperature, scalar and vector velocity, and derived neutral parameters such as horizontal neutral winds and exospheric temperature. Spatial coverage of the system was greatly augmented in 1978 with the addition of a 46 meter fully steerable antenna to complement the existing 68 meter zenith profiler antenna and megawatt class UHF transmitters.
The subauroral location of Millstone Hill (L ~ 3.5) allows access to a full range of ionospheric features and plasma instabilities in the very dynamic plasmaspheric boundary layer, a term introduced by Carpenter and Lemaire (2004) to describe the region where the cool, dense plasma of the inner plasmasphere overlaps the hot, tenuous plasma associated with the ring current / region 2 and plasma sheet footprints. Energy exchange in this layer forms part of the critically important mesoscale stormtime plasma redistribution circuit which brings large storm enhanced density (SED) plumes from tropical latitudes across continental North America. Large westward subauroral polarization stream electric fields, part of the region 2 current closure system, overlap the edges of SED plumes and help to supply substantial cold O+ flux to the high latitude cusp region where it can participate in the creation of tongues of ionization, cross-polar cap transport, and heavy ion outflow which mass loads the plasma sheet. During large disturbances, the Farley-Buneman two stream instability provides coherent scatter structures with radar cross sections up to 90 dB over incoherent scatter levels, allowing microscale probing of electric fields in the SAPS/sub-auroral region.
In this presentation, we will review the types of mid-latitude features seen in Millstone Hill observations. In particular, we will highlight those processes in the upcoming solar maximum which will benefit from synergistic satellite, HF and ISR measurements using Millstone and DMSP with the extended American sector mid-latitude and polar coverage of the SuperDARN network. These topics form ideal opportunities for collaborations with the SuperDARN science community.