OPTICAL INTERFEROMETRIC STUDIES OF THE NIGHTTIME EQUATORIAL THERMOSPHERE - ENHANCED TEMPERATURES AND ZONAL WIND GRADIENTS

Fabry-Perot interferometric observations at 630 nm of equatorial therm ospheric winds and temperatures in the four cardinal directions and ze nith from Arequipa, Peru, during local winter for moderate and high so lar fluxes Showed elevated temperatures over the Andes Mountains that persisted;through the night. The difference in temperature between eas t;and west observations was typically similar to 100 to 200 K for mode rate flux values and as high as 400 K at solar maximum. Correlated wit h these localized heating regions were differences in the zonal thermo spheric wind of 50 to 70 m/s for observations to die west and to the e ast of the Arequipa observatory. Also noted in these periods for the r egion over the Andes was the increased variance of the temperature val ues above the measurement error. These effects of increased variabilit y and localized heating were not observed at solar minimum. The lack o f a significant local time dependence in the diurnal variation of the temperature enhancements suggests that the origin of the heating canno t be related to the coupling of the electrodynamics of the ionosphere to the thermosphere, Instead the hypothesis is advanced that gravity w ave energy from the surface penetrates into the thermosphere, where vi scous dissipation causes the heating. Such wave activity would also ex plain the increased variability of the temperatures for the thermosphe re regions over mountainous terrain.