Effect of the solar eclipse of 22 July 1990 at mid-latitude path of HF propagation

Observational results obtained during the solar eclipse of 22 July 1990 using the oblique sounding method for a midlatitude, Irkutsk to Nizhny Novgorod path are presented. A chirp sounder with high time delay and frequency resolution was used in the measurements. The electron density profile for the mid-point of the path was restored using the reduction method. It is shown that, during the solar eclipse with maximum obscuration similar to 70%, the electron density in the F-region decreased by 6-8% compared with control day values. Travelling ionospheric disturbances caused by the eclipse-generated acoustic gravity waves were detected. Strong variations in the difference group delays (Delta tau) between the high-angle and low-angle rays with a period similar to 40 minutes associated with the start and end of the eclipse, were found. The vertical component of the disturbance speed determined from the time delay oscillation, Delta tau, relative to the eclipse start for the ozone layer (near an altitude of 45 km) of the sub-ionospheric point for the 1F2 mode reflection reaches a value similar to 230 m/s. (C) 1998 Elsevier Science Ltd. All rights reserved.