Diurnal variation of neutral and charged particle temperatures in the equatorialFregion

Abstract

Thomson scatter electron and ion temperature (Te and Ti) profiles from Jicamarca, Peru, near the magnetic equator are discussed. The temperature of the neutral atmosphere (Tn) can easily be deduced from Te and Ti measurements made near the equator because Te - Tn is small (near 0°K at night; near 100°K around 400 km by day). The diurnal variation of Te and hence of Tn at 400 km is as follows: Te increases at an almost constant rate of about 16°K/hr from about 0800 to 1600 hr, then decreases rapidly near sunset. It decreases at an almost constant rate of about 10°K/hr from about 2100 hr until sunrise. The diurnal variations of Qei, the electron-ion heat transfer rate, are found to be consistent with the Tn variations deduced; e.g., the measured Qei, which is approximately proportional to n(O) at 300 km, reaches a maximum about 1600 hr, as does Tn. Daytime Te and Ti values are nearly equal and constant over an altitude range of 100 to 200 km near and above the electron concentration (Ne) maximum. Theory predicts Te - Ti will decrease, and Ti - Tn will increase with height, with Te nearly constant, if the Ne profile is as broad as usual near the magnetic equator. Nighttime Te and Ti values are nearly equal and constant over the 200- to 1000-km altitude range. Thus the nighttime heat input is unmeasurably small, less than a few ev/cm³ sec in the equatorial F region.