A statistical survey of heat input parameters into the cusp thermosphere

摘要

Based on three winters of observational data, we present those ionosphere parameters deemed most critical to realistic space weather ionosphere and thermosphere representation and prediction, in regions impacted by variability in the cusp. The CHAMP spacecraft revealed large variability in cusp thermosphere densities, measuring frequent satellite drag enhancements, up to doublings. The community recognizes a clear need for more realistic representation of plasma flows and electron densities near the cusp. Existing average value models produce order of magnitude errors in these parameters, resulting in large underestimations of predicted drag. We fill this knowledge gap with statistics-based specification of these key parameters over their range of observed values. The European Incoherent Scatter Svalbard Radar tracks plasma flow V-i, electron density N-e, and electron, ion temperatures T-e, T-i, with consecutive 2-3 min windshield wipe scans of 1000 x 500 km areas. This allows mapping the maximum T-i of a large area within or near the cusp with high temporal resolution. In magnetic field-aligned mode the radar can measure high-resolution profiles of these plasma parameters. By deriving statistics for N-e and T-i, we enable derivation of thermosphere heating deposition under background and frictional drag-dominated magnetic reconnection conditions. We separate our N-e and T-i profiles into quiescent and enhanced states, which are not closely correlated due to the spatial structure of the reconnection foot point. Use of our data-based parameter inputs can make order of magnitude corrections to input data driving thermosphere models, enabling removal of previous twofold drag errors. Plain Language Summary Input of energy into the polar ionosphere from the solar wind causes local heating and upwelling of air in the region known as the "cusp." This upwelling in turn dramatically changes the density of the atmosphere as it rises, which has consequences for atmospheric composition and transport as well as for spacecraft that experience increased drag and possibly shortened lifetimes. We show that because of the highly dynamic nature of the cusp, long-term averages and models will not accurately reproduce the energy input to the cusp and the consequent upwelling of the air. We use empirical data to show that the energy input is highly dynamic and that it is necessary to separate active and quiet periods when modeling heating and upwelling in the cusp, as well as to detect or predict accurately where the cusp is located. We present statistical models of the active and quiescent cusp ionization density and temperature of the ionized gas. Occurrence rates of heating events in and near the cusp are estimated by using rapid radar scans covering a large area.