The Spread-F Effect as an Indicator of Troposphere – Ionosphere Coupling

Abstract

The spread F effect is analyzed as a manifestation of troposphere – ionosphere coupling. The observational data discussed were obtained in 1993 through 2003 at the Ukrainian Antarctic Station Akademik Vernadsky (known as Michael Faraday of UK until 6 February, 1996). Among the parameters of atmospheric ‘surface’ weather one has been identified as possessing the strongest statistical connection with the observation probability of spread F. This parameter at Vernadsky is the North – Eastern projection of tropospheric wind speed. Indeed, the conditional probability of detecting spread F in winter was higher by a factor of four with the North – Eastern speed projection of positive rather than negative sign. In the seasonal run, the highest impact of the troposphere upon the upper ionosphere condition was in winter. As for diurnal variations, the tropospheric effect is highest at night and during twilight hours. These observational findings have been interpreted within the hypothesis of atmospheric gravity waves (AGW) propagating through the atmosphere. It has been suggested that AGWs are excited by atmospheric fronts, whose convenient local indicator in the near-Earth troposphere is the North – Eastern wind speed projection. The observed diurnal and seasonal variations in the amount of effect of tropospheric AGW upon the ionosphere might be due to varying conditions of AGW propagation through the atmosphere.