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

The diurnal, seasonal and latitudinal variations of ion temperature (T-i) measured by the Indian SROSS C2 satellite at equatorial and low latitudes along 75degreesE during the solar minimum period of January 1995 to December 1996 are investigated. The satellite covered the latitude belt of 31degreesS-34degreesN within the longitude range of 40degrees-100degreesE at an average altitude of similar to500 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 similar to3000 K occurs in the pre-sunrise hours (04:00-06:00 LT). An afternoon increase of about similar to200 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 (IRT) 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. (C) 2004 Elsevier Ltd. All rights reserved.