On the thermal electron energy balance in the ionosphere in January 1993 and June 1990

This paper examines the electron energy balance in the F region of the ionosphere at Millstone Hill in January 1993 by comparing model electron temperatures with measurements from the incoherent scatter radar. Initial modeling indicated three problem areas for the electron temperature at the height of the peak electron density. First, the nighttime temperature was much too low. Second, the afternoon temperature was a little lower than the measured temperature. Third, the model temperature was too high in the morning just after sunrise. A new algorithm is presented for using the measured topside electron temperature to determine the amount of plasmaspheric heating. It was found that the plasmaspheric heating from photoelectrons escaping the ionosphere must be doubled in order for the model to reproduce the observed topside temperature. With this increased plasmaspheric heat flux, the model temperature at the peak height was also much closer to the measured temperature at night. The low temperature in the afternoon could be easily explained by nominal errors in the model inputs or the radar measurements, but the high model temperatures in the morning remain unexplained. Examination of the cooling rates showed that ion cooling is the main cooling rate and is clearly dominant in the afternoon, while O fine structure cooling is equally important in the morning and at night in January 1993. In order to provide a reference, model-data comparisons were also for June 1990. In this case the agreement between model and data was excellent at all times without the need to adjust local heating and cooling rates. For these summer conditions, vibrationally excited N2 and ion cooling were the two main cooling mechanisms. As was the case in January 1993, doubling of the plasmaspheric heating rate was also needed for the model to match the topside electron temperatures in June 1990. The daytime peak plasmaspheric heat flow deduced from the topside electron temperature showed little variation between June 1990 and January 1993 despite the different seasons and levels of solar activity.