We have reexamined incoherent scatter radar data on electron and ion temperature from the Jicamarca Radar Observatory (12 ¿S, 77 ¿W; 1 ¿N diplat) for the period 1967--68 and early 1969. We find clear evidence of systematic nighttime temperature increases presumably associated with the ''midnight pressure bulge'' and the collapse of the middle latitude F region. A significant new finding is that the temperature enhancements tend on the average to occur about two hours before midnight in the local summer and about one hour after midnight in the local winter. The bulges appear in various shapes and the enhancement magnitudes vary considerably from barely detectable to many tens of degrees Kelvin, but show a definite tendency to be smaller in winter than in summer, when increases of up to 200 K are sometimes observed. Changeover from ''summer'' to ''winter'' behavior occurs within two months or less around equinox. Our results are consistent with the hypothesis of a nighttime equatorial temperature bulge moving with the antisolar meridian, but at Jicamarca systematically centered ~30¿ west of this meridian (~2 hrs before midnight) near the December solstice and ~15¿ east of it near the June solstice. Our data have relevance to the questions of seasonal changes in the phase and amplitude of the tidal modes responsible for the midnight pressure and temperature bulge.