Diurnal, seasonal and latitudinal variations of ionospheric temperatures of the topside F region over the Indian region during solar minimum (1995-1996)

The diurnal, seasonal and latitudinal variations of ionospheric electron and ion temperatures have been measured by the RPA payload aboard the SROSS-C2 satellite during low solar activity (mean sunspot number is 13.9). The satellite data have been selected over the Indian region from 5°N to 35°N latitude and from 65°E to 95°E longitude, at an average altitude of ∼500km. The data analysis shows that the electron and ion temperatures are minimum during night hours and maximum during sunrise hours (from 5:00 to 7:00 LT). A secondary enhancement in electron temperature has also been observed during sunset hours (from 16:00 to 18:00 LT). The peak at sunrise has been observed during all seasons, in both electron and ion temperature. Further, the ionospheric temperatures vary with latitude in the daytime. However, no latitudinal variation has been observed during the nighttime in the latitude range covered in the present study. Comparison of the measured ionospheric 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; the IRI model fails to shows the secondary (dusk) enhancement of the electron and ion temperatures.