Periodic fadings in VHF radio-satellite transmissions during the solar eclipse on 23 October 1976

Abstract

THE localised time-dependent cooling action of the lunar shadow during an eclipse may generate gravity waves at ionospheric heights^1,2. The bow wave thus formed would be detected at great distances from the eclipse path. Experimental data in the northern hemisphere from the eclipse on 7 March 1970, indicated the presence of gravity waves in the F-region, deduced from the incoherent backscatter technique³, vertical incidence soundings⁴, and recordings of the Faraday rotation angle of VHF transmissions from geostationary satellites⁵. The detected travelling ionospheric disturbance (TID) had the horizontal phase velocity of 400m s⁻¹ (ref. 4) and 620±120 m s⁻¹ (ref. 5). TID was reported to travel north to south⁴, or 279±25° east of north⁵. We report here our observations of large-magnitude periodic fadings during the eclipse of 23 October 1976, which indicate that the eclipse is associated with generation of wave disturbance affecting radio-satellite transmissions in the upper VHF. The waves had a 40-km wavelength, and propagated from north to south with a velocity of 556 m s⁻¹.