In situ and remote sensing of thermospheric winds during the energy budget campaign

This paper summarizes the dynamical information obtained in the lower thermosphere during the Energy Budget Campaign, by three experimental techniques: rocket-borne falling spheres instrumented with accelerometers and Tri-Methyl-Aluminium (TMA) trails, and from a ground-based Fabry-Perot interferometer. Winds of 200–400 m/sec, accelerated by the momentum and energy inputs from the magnetosphere, were observed during the ‘B’ and ‘A2’ salvos (15/16 Nov 1980 and 30 Nov/1 Dec resp.), with perturbations as low as 100 km altitude during the ‘B’ salvo. A global model has been used to simulate the wide-scale consequences of these disturbances, and to aid estimation of the integrated energy and momentum inputs.     

OpenGGCM Simulations for the THEMIS Mission

The THEMIS mission provides unprecedented multi-point observations of the magnetosphere in conjunction with an equally unprecedented dense network of ground measurements. However, coverage of the magnetosphere is still sparse. In order to tie together the THEMIS observations and to understand the data better, we will use the Open Geospace General Circulation Model (OpenGGCM), a global model of the magnetosphere-ionosphere system. OpenGGCM solves the magnetohydrodynamic (MHD) equations in the outer magnetosphere and couples via field aligned current (FAC), electric potential, and electron precipitation to a ionosphere potential solver and the Coupled Thermosphere Ionosphere Model (CTIM). The OpenGGCM thus provides a global comprehensive view of the magnetosphere-ionosphere system. An OpenGGCM simulation of one of the first substorms observed by THEMIS on 23 March 2007 shows that the OpenGGCM reproduces the observed substorm signatures very well, thus laying the groundwork for future use of the OpenGGCM to aid in understanding THEMIS data and ultimately contributing to a comprehensive model of the substorm process.     

Initial results of the evaluation of IRI hmF2 performance for minima 22–23 and 23–24

The performance of the International Reference Ionosphere (IRI) in predicting the height of the maximum of electron density (hmF2) has been evaluated for similar geomagnetic latitudes stations in the northern hemisphere (NH) and southern hemisphere (SH), and for the last two minima. As truth-sites, the digisonde stations of Millstone Hill (42.6°N, 288.5°E), USA, and Grahamstown (33.3°S, 26.5°E), South Africa, were considered. A monthly averaged diurnal variation was obtained from all the observations and model output in the months studied, and the corresponding difference was also calculated. For this initial study data from summer and winter in the NH and SH were selected for the solstice comparison, and October data for both stations were used to represent equinox conditions. The choice of these periods depended on data availability and quality. The results show that for the earlier minimum in 1996, in general IRI hmF2 values are in reasonable agreement with the observations. The exceptions are October and December in the SH, where IRI hmF2 tends to high, particularly on the dayside, and also July for which the daytime measured values tend to be larger than the IRI ones. For the recent minimum in 2008, IRI tends to over-estimate the hmF2 in most of the observations. The results support the general assertion that thermospheric temperatures were cooler during the last solar minimum as a consequence of an unusually low, and extended, minimum in solar extreme-ultraviolet flux, and in response to continually increasing long-term trend in anthropogenic carbon dioxide. The cooler temperatures not only decrease density at a fixed height, but also make the corresponding contraction of the atmosphere lower the height of the F-region peak.