First observational study during a solar eclipse event on variations in the horizontal winds simultaneously in the troposphere-stratosphere-mesosphere-lower-thermosphere region over the equatorial station Thumba (8.5°N, 77°E)

The longest annular solar eclipse of the millennium occurred on 15 January, 2010, and was visible over the equatorial station Thumba (8.5°N, 77°E) around noon time. A host of experiments were carried out to study the variations due to the solar eclipse event on various geophysical parameters, from the Earth’s surface to ionospheric heights. The present study focuses on the variation in the horizontal winds in the height regions of 0–65 km and 80–100 km, using GPS-sondes, rocket-sondes and meteor wind radar. The observations were made during, and after, the maximum obscuration on the day of the eclipse, as well as at the same time on a control day. The observations showed a strengthening/weakening of winds along with directional changes both in zonal and meridional winds in the selected height domains. A drastic change from easterly to westerly is observed at 98 km during, and after, the maximum phase, but, for the meridional wind, the reversal is observed only after the maximum phase. Variations due to the eclipse were also observed around the tropopause and stratopause in both wind components. However, the observed changes in winds around the tropopause and stratopause could not be attributed unambiguously to the eclipse as day-to-day wind variability is not available in these height regions. The significance of the present study lies in reporting the variations in the horizontal wind components from the ground to the 100-km height region (with a gap around 65–80 km), and the characteristics of the atmospheric waves generated due to the mid-day annular solar eclipse.