Ionospheric and magnetic observations during the annular solar eclipse of November 23, 1965

Vertical-incidence (VI) ionograms, magnetograms, and relative VI signal-amplitude (7-MHz) data were obtained in Bangkok, Thailand, during the annular solar eclipse on 23 November 1965. A maximum of 86% obscuration of the solar disk was observed at about 1007 local time (0307 GMT) in Bangkok, which was approximately 290 km from the center of the eclipse path. Marked changes in F2-layer virtual height and considerable stratification of the F layer, including formation of an F1.5 layer, were observed. Magnetograms indicate a large (approximately 25%) diminution in ionospheric current relative to normal solar daily (Sq) variations.