Co-investigator Philip Erickson
Project Website http://www.nsf.gov/awardsearch/showAward?AWD_ID=1243058&HistoricalAwards=false
Project Start Date July 2013
Project End Date June 2017
During geomagnetic storms the region of the ionosphere that lies just equatorward of the auroral zone is often perturbed by a longitudinally-extended channel of high-speed (>1 km/s) plasma flow known as the sub-auroral polarization stream (SAPS). The investigators will analyze observations of ionospheric disturbances through the current period of solar cycle maximum with the aim of deriving a comprehensive, observationally based model of SAPS. The study will examine the onset, spread, and decay of SAPS flows and chart the accompanying changes observed in total electron content (TEC). Coordinated experiments will be conducted with the recently refurbished Incoherent Scatter Radar (ISR) at Millstone Hill in order to relate the SAPS electric field dynamics to changes in ionospheric density and chemistry and to gauge their effects on the neutral atmosphere. The SAPS phenomenon is associated with strong poleward-directed electric fields (>50 mV/m) and a deep depression, or trough, in ionospheric densities. SAPS is believed to be a consequence of a feedback process whereby magnetic field-aligned current of magnetospheric origin closes across the ionospheric trough, eliciting chemical changes that further reduce the ionospheric density while increasing the electric field in a manner that maintains current continuity.
The SAPS phenomenon has important consequences for structuring ionospheric plasma, ionospheric composition, formation of plasma irregularities, and coupling to the neutral atmosphere. The attainment of a comprehensive, observationally-based understanding of SAPS and its impacts on the thermosphere would be a major advance. SAPS has traditionally been studied with single radars and satellites, leading to characterizations that are limited in their utility for understanding the evolution and impacts of SAPS as a multi-dimensional, global-scale phenomenon. Recent advances in observational techniques have fundamentally altered the research landscape. The construction of a mid-latitude chain of SuperDARN radars in North America has made possible simultaneous (~1 min) views of SAPS plasma flows and electric fields across many hours of MLT while the expansion of the network of Global Positioning System (GPS) receivers has made possible continental-scale mapping of TEC on similar time scales.
Initial comparisons indicate that the SAPS observed by the radars are seated in an enhanced trough-like density feature that is mapped by TEC. This work will lead to the development of a phenomenological model of SAPS that is suitable for testing theoretical ideas and the development of storm-time ionospheric models, the dissemination of global-scale information on recent SAPS events to the wider community, the increased application of the GPS TEC database to scientific research, and the instruction of scientists on the use of these data. In addition, a graduate student at Virginia Tech will be trained in the new experimental techniques and in the merging of data from the SuperDARN radars, GPS, and incoherent scatter radar.