Quasi-periodic fluctuations in electron content during a partial solar eclipse

Abstract

CHIMONAS and Hines1,2 have suggested that a solar eclipse might generate gravity waves in the atmosphere. During solar eclipse the localised cooling of the atmosphere in the lunar shadow causes an energy imbalance and the shadow moving at supersonic speed across the Earth's surface could be a continuous source of gravity waves propagating to great distances in the atmosphere. These quasi-periodic wave perturbations in the ionospheric electron density, caused by the coupling between the ionised and the neutral particles, have been detected by various investigators3–5 at middle and high latitude stations away from the path of the eclipse shadow. Hajkowicz6 has reported the observation of perturbations of quasi-peniods of less than 2 min, after the October 1976 eclipse. We report here the observation of quasi-periodic fluctuations in Faraday rotation angle Ω and the 1 MHz modulation phase delayφ of 40 MHz transmissions from ATS-6 geosynchronous satellite recorded at Trivamdrum (dip 0°57′S, geographical longitude 76°57′E) during the partial solar eclipse on 29 April 1976. φ directly gives columnar electron density integrated along the radio ray path from the satellite to the receiver; whereas Ω gives columnar integrated electron density only up to an altitude of 2,000 km because of the weightage by the component of the geomagnetic field along the ray path. For ATS-6 to Trivandrum ray path geometry, a change of 10° in Ω will be produced by a change of 0.47×1016 el. m–2 of electron (el.) content. In contrast to this, 10° change in φ will be produced by a change of 0.34 × 1015el. m–2. The accuracy of measurement of both Ω and φ is better than 1°.