Effect of solar activity on ionospheric temperatures in F2 region

319-325Ionospheric F-region is very dynamic and highly depends on the solar cycle. In the present study almost half of the solar cycle from January 1995 to December 2000 (from solar minimum to solar maximum) satellite data were used. The data were recorded with the help of Retarding Potential Analyzer (RPA) payload aboard Indian SROSS-C2 satellite at an average altitude of 500 km over the Indian region. The data analysis shows that the nighttime average ionospheric electron and ion temperatures show a positive correlation with solar activity. However, the sunrise peak values show anti-correlation with solar activity. Further the ratio of sunrise average peak value and nighttime average show a negative correlation with the solar activity, both for electron and ion temperatures. A sudden enhancement at sunrise has been observed during all seasons, in both electron and ion temperatures. Comparison of the measured ionospheric electron and ion temperatures with the predicted values from the international reference ionosphere (IRI) reveals that the peak during sunrise hours is slightly underestimated by the IRI model