FIRST RESULTS FROM GROUND-BASED DAYTIME OPTICAL INVESTIGATION OF THE DEVELOPMENT OF THE EQUATORIAL IONIZATION ANOMALY

A meridional scanning OI 630.0-nm dayglow photometer was operated from Ahmedabad (17.2 degrees N dip lat.) scanning a region towards the sou th in the upper atmosphere extending over similar to 5 degrees in lati tude from 10.2 degrees N to 15.2 degrees N dip latitude. From the spat ial and temporal variabilities of the dayglow intensity in the scannin g: region we show for the first time: evidence for the passage of the crest of the equatorial ionization anomaly (EIA) in the daytime by mea ns of a groundbased optical technique. The relationship between the da ytime eastward electric field over the dip equator in the same longitu de zone as inferred from the equatorial electrojet strength and the ev olutionary pattern of EIA is clearly demonstrated. The latter as infer red from the dayglow measurements is shown to be consistent with our p resent understanding of the electrodynamical processes in the equatori al region. The present results reveal the potential of this ground-bas ed optical technique for the investigation of ionospheric/thermospheri c phenomena with unprecedented spatial and temporal resolution.