Evidence for orographic wave heating in the equatorial thermosphere at solar maximum

Fabry Perot interferometer observations of equatorial 630 nm airglow thermospheric winds and temperatures were made at Arequipa, Peru (16.5 S, 71.5 W) during the solar maximum years of 1989 and 1990. Examination of the thermospheric winds measured from Doppler shifts of the 630 nm airglow emission in the two directions east and west of Arequipa shows that the zonal wind is often significantly weaker over the Andes (east) than over the Pacific (west) in winter. Between 19 LT and 24 LT, the typical reductions in speed found were similar to 40 to 70 m/s. In the same time period the temperature results show elevated values of similar to 200-500 K for the three directions (north, east, and zenith) over mountainous terrain compared with those ol the two directions (west and south) over water. This effect fades near equinoctial periods. Examination of the standard deviation of the temperature observations for the five directions showed an increase in this value above the measurement error by a factor of three for the direction toward the Andes (East) but not for the direction over water (South); this elevation is consistent with wave activity as a source of the heating. Viscous dissipation of waves propagating into the thermosphere region from below is suggested as an explanation for the localized regions of heating.