Abstract
A CCD based all-sky (180° field view) airglow imaging system was operated from a low latitude station, Kolhapur (16.8°N, 74.2°E; 10.6°N dip lat.) in India to map the thermospheric motion and to study the low latitude ionospheric irregularities by measuring the nightglow signatures at 630 nm. In general, all-sky imaging techniques offer broad, instantaneous coverage (2.5 million sq km area at 150° field of view at 300 km height) of the spatial and temporal characteristics of the airglow features from the selected layers of the thermosphere and ionosphere system. In addition to the all-sky camera, photometer and radio scintillation observations together with ionospheric soundings were carried out from Kolhapur to verify the signature of small scale as well as large scale size F-region irregularities. Initial results from these measurements display good examples of north-south motion of the thermosphere with apparent drift speeds of 143-200 m/s during geomagnetically quiet nights. The north-south aligned (>1000 km) bands of plasma depletions or bubbles with east-west dimension of 50-250 km moving with drift speed of 140 m/s towards east have been observed. The zonal component of plasma drift speed matches well with the eastward component of the neutral speed computed using Hedin's recent model. However, the meridional components of plasma drift speed are generally higher than the components of the neutral wind speed computed using the model. The results confirm the earlier quantitative investigations of equatorial depletion characteristics from Brazil and elsewhere.
