Solar cycle variations of mid-latitude electron density and temperature: Satellite measurements and model calculations

This paper presents an analysis of a large database of in-situ topside ionosphere electron densities (N-e) and temperatures (T-e) from three decades of satellite measurements with the ultimate goal of improving the International Reference Ionosphere (IRI) model. The satellite data, which range from the early Explorers to the more recent KOMPSAT and DMSP satellites, are examined to reveal the variation of the mid-latitude N-e and T-e at altitudes of 550, 850, and 2000 km as a function of solar activity for different local times, and seasons. Comparisons with IRI, the FLIP physical model, and the Millstone Hill incoherent scatter radar empirical model help to determine how consistent these satellite-observed variations patterns are with the current IRI model, with the theoretical expectations and with ground-based results. For N-e good agreement is found between the data and models in terms of variations pattern as well as absolute values. Whereas N-e always increases with solar activity, T-e can increase, decrease, or stay constant depending on the specific altitude, local time and season. At 550 km the daytime T-e increases with solar activity in summer, decreases in equinox and stays almost constant in winter. At this altitude range we find generally good agreement between the variations seen with the satellite data and those predicted by the FLIP and Millstone Hill models. At 850 km, however, significant discrepancies are noted. The satellite data, primarily DMSP in this altitude range, are consistently higher than the Millstone Hill model averages and include unrealistically high temperatures (4000-5000 K) at very low solar activities. The FLIP model also predicts much lower values at low solar activities but otherwise (for middle to high solar activities) agrees well with the satellite data. During nighttime the FLIP model underestimates T-e at 850 and 2000 km altitude for the summer and equinox seasons. The current IRI T-e model does not include variations with solar activity. The IRI values are generally in between the satellite and radar averages with a few exceptions. (C) 2007 Published by Elsevier Ltd on behalf of COSPAR.