Thermospheric vertical winds above Mawson, Antarctica

Abstract

High-resolution (R ≅ 200,000) night-time Fabry-Perot spectra of the λ630 run OI thermospheric airglow emission obtained from Mawson, Antarctica, during the austral winter of 1992 have been used to provide estimates of thermospheric temperature and neutral wind. In this paper, we report on characteristics of the resulting vertical wind estimates. The final data set comprised 103 observing nights between 18 March and 20 September for a total of 2096 useable zenith spectra. Because the instrumental reference rest wavelength of the 7630 nm emission is not known, this experiment was only capable of measuring vertical wind variations relative to an arbitrarily-chosen reference velocity. For this work, we established our reference by requiring that the nightly mean vertical wind be zero. We have divided our data into two subsets, corresponding to days of quiet and moderately disturbed magnetic activity. In both cases, the mean daily variation in vertical wind velocity was dominated by its diurnal component with downward winds (relative to our chosen zero, and negative) appearing prior to local magnetic midnight and upward (positive) winds after. Averaged over all days of low magnetic activity, the diurnal range was −2.6 to 3.0 m s−1 whilst for days of moderate activity, it was −6.8 to 4.1 m s−1. Superimposed on this mean vertical wind are fluctuations at shorter periods than our sampling interval of 1 h. We estimate the distributions of vertical velocities prevailing during our observations to be characterized by one-sigma halfwidths of 14.3 and 18.7 m s−1 for low and moderate magnetic activity, respectively. This experiment has yielded generally smaller estimates of vertical wind speeds than those reported by previous authors from auroral latitudes for similar levels of magnetic activity. Comparison is also made with the UCL thermospheric general circulation model.