Variation ofF-region nighttime neutral temperatures with equatorial spread-F activity

NighttimeF-region temperatures have been obtained over Mount Abu (24·6°N, 72·7°E geographic, 15·0° geomagnetic latitude) by monitoring OI 6300 Å line widths, using Fabry-Perot spectrometer. Enhancement in neutral temperatures associated with spread-F activity over Thumba (8·5°N, 76·8°E geographic, 0·6°S geomagnetic), which is on the magnetic equator were reported earlier. Additional data over Mt Abu for seven days bring out the following major features. (i) In theF-region over Mt Abu, the neutral temperature enhancements upto 200°K are observed on most of the nights when there is spread-F activity over the magnetic equator. (ii) There are no occasions which show temperature enhancements over Mt Abu without spread-F activity over the equator. On such occasions the observed atmospheric temperatures agree very well with those calculated on the basis of the Jachhia atmospheric model, both for magnetically quiet as well as disturbed days. (iii) There is a good indication that the increase inF-region temperature over Mt Abu is delayed with respect to the onset of spread-F over Thumba by approximately 15–30 min.