The midlatitude ionosphere during the total solar eclipse of March 9, 1997

The total solar eclipse of March 9, 1997, was visible from some regions of China, Mongolia, and East Siberia during 0045-0130 UT. The eclipse coincided with a relatively long geomagnetically quiet period. During the total solar eclipse, the observations included oblique-incidence ionograms recording; also measurement the total electron content along specified directions to the visible Global Positioning System satellites and the Doppler sounding on various HF ray paths over the region under consideration were carried out. This paper presents results derived from studying the spatial pattern of midlatitude ionospheric response to this eclipse on the basis of a numerical simulations. Calculations have been executed using a model for ionosphere-plasmasphere coupling. Comparison of model results with data of all measurements showed a good qualitative and quantitative agreement. It is shown that by and large the behavior of the ionosphere during the eclipse manifests itself as a short-lasting (similar to 1-hour) rearrangement to nighttime conditions with the ion flow directed downward from the plasmasphere, as a rise of the F-2 layer maximum by about 20 km, and as a twofold increase in electron density at the height of the maximum during the eclipse's totality phase; The electron temperature decreases by 200-400 K, while the ion temperature drops only slightly. It is found that changes in the spatial distribution of electron density along the HF ray paths during the eclipse give rise to variations of Doppler frequency shift with amplitudes of about 1 Hz and a duration of about 120 min. The findings reported in this paper do not validate the hypothesis that solar eclipses generate atmospheric gravity waves and associated traveling ionospheric disturbances.