First simultaneous lidar observations of sodium layers and VHF radar observations of E-region field-aligned irregularities at the low-latitude station Gadanki

摘要

Simultaneous observations of atmospheric sodium (Na) made by a resonancelidar and E-region field-aligned-irregularities (FAI) made by the Indian MSTradar, both located at Gadanki (13.5° N, 79.2° E) and horizontal windsacquired by a SKiYMET meteor radar at Trivandrum (8.5° N, 77° E) areused to investigate the relationship among sodium layer, FAI and neutralwinds in the mesosphere and lower thermosphere region. The altitudes anddescent rates of higher altitude (~95 km) Na layer and FAI agree quitewell. The descending structures of the higher altitude Na layer and FAI arefound to be closely related to the diurnal tidal phase structure in zonalwinds observed over Trivandrum. At lower altitudes, the descent rate of FAIis larger than that of Na layer and zonal tidal phase. These observationssupport the hypothesis that the metallic ion layers are formed by the zonalwind shear associated with tidal winds and subsequently get neutralized tomanifest in the form of descending Na layers. The descending FAI echoinglayers are manifestation of the instabilities setting in on the ionizationlayer. In the present observations, the altitudes of occurrence of Na layerand FAI echoes being low, we surmise that it is quite possible that the FAIechoes are due to the descent of already formed irregularities at higheraltitudes.