VARIABILITIES IN THE THERMOSPHERIC TEMPERATURES IN THE REGION OF THE CREST OF THE EQUATORIAL IONIZATION ANOMALY - A CASE-STUDY

Results on spectroscopic measurements of thermospheric temperatures ma de from a low latitude station, Mt Abu (24.6 degrees N, 72.7 degrees E , geographic; 18 degrees N dip latitude), India, situated in the crest region of the equatorial ionization anomaly (EIA), are presented. On many occasions, these measurements reveal large deviations from the pr edictions of the neutral atmospheric model, MSIS-86, bringing out its limitations as applied to the equatorial and low latitude thermosphere . The role played by large-scale geophysical processes like the EIA, e quatorial spread F (ESF) and the midnight temperature maximum (MTM), a ll of which influence the thermal structure of the upper atmosphere, i s examined in the context of explaining the differences between the me asured temperatures and model predictions. It has been conclusively sh own that Joule heating associated with ESF irregular electric fields i s not solely responsible for the observed deviations, and the possibil ity of a significant role by the EIA related processes is indicated.