Abstract
Abstract. Recent studies of the ion energy balance in the mid-latitude ionosphere have led to the suggestion that hot neutral atomic oxygen may play a significant role; the presence of a population of hot O could explain some of the problems met in balancing the ion energy budget for Incoherent Scatter (IS) observations. The aim of the present study is to look at such effects by using numerical simulation. The TRANSCAR model is a time-dependent, 13-moment ionosphere model developed for high latitude studies. It was first adapted for mid-latitude conditions. In a first step the model was calibrated and cross-checked with St. Santin IS measurements for the winter case of 27 January 1972 around noon using, in particular, the MSIS neutral atmosphere model. This provides a reference diurnal variation of the ionosphere. The second step investigated the influence of a maxwellian population of hot neutral atomic oxygen introduced in addition to the standard neutral atmosphere. The paper describes the initial comparison between the model and St. Santin IS data, and then the effects induced by a hot atomic oxygen population.Key words. Ionosphere (ionosphere-atmosphere interactions; ion chemistry and composition; mid-latitude ionosphere)
Highlights
There is more and more evidence that a hot part of the oxygen velocity distribution exists and plays an important role in thermosphere-ionosphere interactions
The simulations with TRANSCAR show that even a small fraction of hot O has a significant impact on the ion energy balance, and affects O determination greatly at certain times of day while the exospheric temperature determination is only modestly affected
Particular deviations are found near sunset/sunrise periods for the densities, even with small fractions of hot O
Summary
There is more and more evidence that a hot part of the oxygen velocity distribution exists and plays an important role in thermosphere-ionosphere interactions. The first evidence was the discrepancy between the oxygen density inferred from incoherent scatter data and that measured by OGO 6: Hedin and Alcaydé (1974) showed individual conjunction agreements for daytime measurements, but significant discrepancies between OGO 6 and St. Santin diurnal variations, in particular, around sunrise and sunset. Another indication was suggested after studies of the collision frequency νO+ −O between ion O+ and the neutral atomic oxygen O, using either the energy balance or momentum balance equation (Oliver and Glotfelty, 1996). These two methods lead to as much as 60% different solutions for the collision frequencies. A recent study of the 630nm airglow emission (Shematovich et al, 1999) led to the conclusion that hot O(1D) emissions have to be taken into account for accurate neutral temperature measurements in the thermosphere. Oliver and Schoendorf (1999) inferred hot oxygen variations from incoherent scatter data, and Schoendorf et al
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