Climatology of the nighttime equatorial thermospheric winds and temperatures over Brazil near solar minimum

Abstract

We report on the climatology of equatorial thermospheric winds and temperatures based on Fabry-Perot interferometer measurements of Doppler shifts and Doppler broadenings of the 630.0 nm spectral emission from the Cajazeiras observatory located in the northeastern part of Brazil (6.89°S, 38.56°W). These results apply to the lower thermosphere region near 240 km and were obtained during a period of weak solar activity with the solar flux typically within the range of 72 and 82 solar flux units. Examination of the monthly averaged meridional thermospheric winds for 1 year of measurement from October 2009 to September 2010 found the wind direction to be equatorward during summer months throughout the early evening hours with maximum speeds reaching ∼65 ms-1. During winter months, the early evening meridional wind direction reversed to poleward with similar speeds. This result is attributed to the cross-hemispheric flow from the summer to winter hemisphere. Superimposed upon this wintertime meridional wind flow was an equatorward surge shortly before midnight. This surge shifted to earlier local times in the transition from the vernal equinox to summer and to later local times between the summer solstice and the autumnal equinox; this flow feature is attributed to tidal wave forcing. The temperature observations exhibited the expected behavior, with the midnight temperature maximum showing a greater amplitude, ∼120 K, in the vernal equinox with somewhat weaker amplitudes, ∼75 K, seen at earlier local times during the summer. Also observed was a phase lag of 60 to 90 min between the appearance of the equatorward meridional wind flow and occurrence of the midnight temperature maximum peak. Copyright 2011 by the American Geophysical Union.