Optical interferometric measurements of nighttime equatorial thermospheric winds at Arequipa, Peru

Abstract

We obtained nighttime measurements of equatorial thermospheric wind dynamics at Arequipa, Peru, with an automated field-widened Fabry-Perot interferometer between April 1983 and August 1983 and reduced data from 62 nights. Significant seasonal variations in both zonal and meridional components of the thermospheric neutral wind vector were observed. Near the equinox, between 2000 and 2300 LT, the zonal wind component is eastward with an amplitude between 100 and 150 m/s that gradually ebbs to zero by dawn. The meridional component is generally small throughout the night. In the winter months (May–August) and at the winter solstice the zonal wind persists eastward throughout the night with speeds between 50 and 150 m/s. The meridional component is directed poleward (southward) toward the winter hemisphere with a speed of 50–75 m/s that decays to zero by midnight. Comparison with the predictions of the National Center for Atmospheric Research thermospheric general circulation model for equinoctial and solstice conditions shows good agreement. We conclude that the observed seasonal changes are caused by the changing nature of the solar forcing function. The Arequipa results found the day-to-day variability in the winter thermospheric winds to be less than that found for the summer equatorial observations obtained at Kwajalein. Interferometric measurements of the 630.0-nm intensity at equinox showed a major reduction of the emission lasting 1 or 2 hours in all directions but south shortly after evening twilight; this decrease was not observed during Winter.