Ion temperature variation observed by ROCSAT-1 satellite in the afternoon sector and its comparison with IRI-2001 model

The ion temperature has been measured with the ionospheric plasma and electrodynamics instrument (IPEI) onboard the first satellite of Republic of China, ROCSAT-1, orbiting at 600 km altitude with a 35° inclination. Global ion temperature distributions in the afternoon sector for different seasons are investigated during the solar maximum year of 2000. The temperature troughs at the dip equator are found to incline and become shallower until the evening temperature enhancement has reached to its peak. The temperature troughs follow with the electron temperature variation through the heat exchange between electrons and ions. The temperature crests in the winter hemisphere are also noticed in the afternoon sector but have a smaller magnitude than those in the morning sector. The magnitudes of the temperature crests are reduced first and then enhanced later as local time increases. The locations of the temperature maxima within the temperature crests shift from longitudes of positive magnetic declination to longitudes of negative magnetic declination during the June solstice and from longitudes of negative magnetic declination to longitudes of positive magnetic declination during the December solstice. Both magnitudes and movements of the temperature crests can be understood with the field-aligned ion flow pattern observed by ROCSAT and are attributed to the change of the neutral wind pattern in zonal direction from westward to eastward. These features from the ROCSAT observations are not available in the IRI-2001 model yet.