Near-continual ground-based nighttime observations of thermospheric neutral winds and temperatures over equatorial Brazil from 2009 to 2012

Abstract

We present measurements of thermospheric neutral winds and temperatures measured by two Fabry–Perot interferometers (FPIs) operating in northeastern Brazil, in the equatorial region, over the period of September 2009 through June 2012. The FPIs observe the Doppler shift and broadening of the nighttime 630.0-nm emission originating at altitudes of approximately 240km. The temperatures indicate a strong dependence on solar flux conditions, as captured by the F10.7 index, which ranged from ∼72 to 175 solar flux units over the duration of the study. The signature of the midnight temperature maximum is seen in the data, recurring each year during the local summer months (October through February). Throughout the year, the thermospheric zonal winds show an initial increase in eastward flow after sunset followed by a reduction in the midnight and early morning hours. This reduction in the zonal flow is most rapid in the local summer months. The thermospheric meridional winds show the expected signature of trans-equatorial flow from the summer to winter hemisphere. Superposed on this during the local summer months is a time of equatorward flow during the mid-evening period, 22–23LT, which is likely a manifestation of the semi-diurnal thermal tidal wave moving upward into the lower thermosphere region from below. The thermospheric neutral winds do not show as much of a dependence on the solar flux as the thermospheric neutral temperatures do, at least for the range of fluxes covered during the study period.