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

Abstract

Abstract. Simultaneous observations of atmospheric sodium (Na) made by a resonance lidar and E-region field-alignedirregularities (FAI) made by the Indian MST radar, both located at Gadanki (13.5 • N, 79.2 • E) and horizontal winds acquired by a SKiYMET meteor radar at Trivandrum (8.5 • N, 77 • E) are used to investigate the relationship among sodium layer, FAI and neutral winds in the mesosphere and lower thermosphere region. The altitudes and descent rates of higher altitude (∼95 km) Na layer and FAI agree quite well. The descending structures of the higher altitude Na layer and FAI are found to be closely related to the diurnal tidal phase structure in zonal winds observed over Trivandrum. At lower altitudes, the descent rate of FAI is larger than that of Na layer and zonal tidal phase. These observations support the hypothesis that the metallic ion layers are formed by the zonal wind shear associated with tidal winds and subsequently get neutralized to manifest in the form of descending Na layers. The descending FAI echoing layers are manifestation of the instabilities setting in on the ionization layer. In the present observations, the altitudes of occurrence of Na layer and FAI echoes being low, we surmise that it is quite possible that the FAI echoes are due to the descent of already formed irregularities at higher altitudes.

A review of latitudinal characteristics of sporadic sodium layers, including new results from the Chinese Meridian Project

“…The direct link between ES and SSLs above 97 was also supported by the observation of Coqui-2 rocket campaign which showed that the SSLs above 97 km were always accompanied by ion layers and those below 97 km usually occurred alone (Friedman et al, 2000). In addition, the results by Beatty et al (1989), Shibata et al (2006) and Sridharan et al (2009) in low latitudes also provided additional evidences to the direct link between Es and SSLs above 97 in low latitudes (Beatty et al, 1989;Shibata et al, 2006;Sridharan et al, 2009). Overall, the coincidence between electron/ion layer and the peaks of the SSL above 97 km in low latitude are supported by increasing number of observations, implying that the ES layer is likely the direct source for the formation of these high altitude SSLs (Friedman et al, 2000;Kane et al, 1993).…”

Investigation of the seasonal and local time variations of the high‐altitude sporadic Na layer (Nas) formation and the associated midlatitude descending E layer (Es) in lower E region

“…On the other hand, even these few observations exhibit somewhat random features that have prevented the community from obtaining a clear understanding of the full characteristics of high‐altitude Na s . Meanwhile, the most recent Na s observations around the globe, through either ground‐based Na lidar [ Sridharan et al ., ; Wang et al ., ; Dou et al ., ] or spaceborne instruments [ Fan et al ., ], have revealed strong seasonal variation of its occurrence frequency with the maximum during the boreal summer and the minimum near boreal winter solstice. These observations also highlight that strong, high‐altitude Na s events are more frequently observed in East Asia around midlatitudes and in the equatorial region of South America [ Batista et al ., ].…”