Ionospheric response to a solar eclipse in the equatorial anomaly region

On October 24, 1995 a solar eclipse occurred with its path of totality passing over southern Asia, but the associated region of its partial eclipse covered almost all of Asia. It was therefore of interest to investigate how the ionosphere responded to this eclipse, especially because the region included the equatorial anomaly region. For this purpose the authors collected and processed ionosonde data from six stations in the region. These data reveal three effects that are coherent geographically in that they cover at least two of these six stations: (1) For the region with geomagnetic latitudes higher than 20 degrees, the N_max increased slightly immediately following the first contact for about 30 minutes. (2) In response to the eclipse, the largest depression occurring roughly 11/2 hours after the maximum obscuration was observed at approximately 14 degrees geomagnetic latitude even though the percent obscuration of the Sun at latitudes lower than 14 degrees was larger. (3) Around 6 hours after the maximum phase another secondary depression in the N_max was observed for geomagnetic lati-tudes lower than 14 degrees. Physical mechanisms that may be responsible for causing these effects are proposed and examined in this paper. They are all related to eclipse-caused dynamic effects.