Comparison of the measured and modeled electron densities and temperatures in the ionosphere and plasmasphere during the period 25-29 June 1990

We present a comparison of the electron density and temperature behavior measured in the ionosphere by the Millstone Hill incoherent-scatter radar during the period 25-29 June 1990, and in the plasmasphere within the Millstone Hill magnetic field flux tube by the instruments on board of the EXOS-D satellite in the Northern Hemisphere between 02:07:56 UT and 02:11:08 UT on 28 June 1990 with numerical model calculations from a time-dependent mathematical model of the Earth's ionosphere and plasmasphere. We have evaluated the value of the nighttime additional heating rate that should be added to the normal photoelectron heating in the electron energy equation in the plasmasphere region above 5000 km along the magnetic field line to explain the high electron temperature measured by the instruments on board of the EXOS-D satellite. The additional heating brings the measured and modeled electron temperatures into agreement with the plasmasphere and into very large disagreement with the ionosphere if the classical electron heat flux along magnetic field line is used in the model. The approach of Pavlov et al. (Annales Geophysicae 18 (2000) 1257-1272) based on an effective electron thermal conductivity coefficient along the magnetic field line, is used to explain the measured electron temperature in the ionosphere and plasmasphere. This approach leads to a heat flux which is less than that given by the classical Spitzer-Harm theory. The evaluated additional heating of electrons in the plasmasphere and the decrease of the thermal conductivity in the topside ionosphere and the greater part of the plasmasphere allow the model to accurately reproduce the electron temperatures observed by the instruments on board of the EXOS-D satellite in the plasmasphere and the Millstone Hill incoherent-scatter radar in the ionosphere. The resulting effect of vibrationally excited N-2 and O-2 on NmF2 is the decrease of the calculated daytime NmF2 up to a factor of 2. The modeled electron temperature is very sensitive to the electron density, and this decrease in electron density results in the increase of the calculated daytime electron temperature up to about 750 K at the F2 peak altitude giving closer agreement between the measured and modeled electron temperatures. Both the daytime and nighttime densities are not reproduced by the model without vibrationally excited N-2 and O-2, and inclusion of vibrationally excited N-2 and O-2 brings the model and data into better agreement. (C) 2001 Published by Elsevier Science Ltd.