Diurnal, seasonal and latitudinal variations of ion temperature measured by the SROSS C2 satellite in the Indian zone equatorial and low latitude ionosphere and comparison with the IRI

摘要

The diurnal, seasonal and latitudinal variations of ion temperature (T_i) measured by the Indian SROSS C2 satellite at equatorial and low latitudes along 75°E during the solar minimum period of January 1995 to December 1996 are investigated. The satellite covered the latitude belt of 31°S-34°N within the longitude range of 40°-100°E at an average altitude of ～ 500 km. Measured T_i varies between 600 and 700 K during nighttime (20:00-04:00 LT) and between 1000 and 1100 K around noon. Enhancement in T_i upto ～ 3000 K occurs in the pre-sunrise hours (04:00-06:00 LT). An afternoon increase of about ～ 200 K over the daytime value is observed between 15:00 and 17:00 LT in summer. Latitudinal gradients in T_i have been observed during the period of morning and afternoon enhancements. The ion temperature also exhibits large variability. Comparison of observed and International Reference Ionosphere (IRI) predicted ion temperature reveals that the IRI overestimates T_i at about all local times and latitudes except during the periods of enhanced T_i.