The results are presented from the study of vertical, seasonal, and latitudinal variations of ion temperature perturbations in the altitude region 100--400 km using measurements at the network of IS radars over a multiyear period. The intensities of ion temperature perturbations having periods less than 6 hours are obtained using the least squares fit filtration of tides from the data. The intensities of the perturbations are maximized in the altitude region 150--180 km at low latitudes. At high latitudes the maxima become much smaller. Seasonal and latitudinal variations of the intensity have different structure below and above 150--180 km. At altitudes below 120--130 km the intensity of the ion temperature perturbations has a maximum in January and a minimum in July at high latitudes, and two maxima (in summer and winter) at low latitudes. Above 150--180 km the intensity of ion temperature perturbations has maxima at high and low latitudes in all seasons. The high-latitude maxima can be attributed to the variations of electric fields and particle precipitation and to the atmospheric waves propagated from below and generated in the auroral region. The reasons for the low-latitude maxima of the intensity are not clear enough. A possible reason may be the increased generation of internal gravity waves by tides in the equatorial upper atmosphere. ¿ American Geophysical Union 1995