Descending ion layer property in the Gadanki radar observations of 150 km echoes and its implication to the echoing phenomenon

Gadanki radar observations of the daytime 150 km echoes displaying descending features, resembling the descending ion layer behavior, are presented. The descending pattern is intriguing since it indicates the possible role of density gradient associated with the ion layer in generating the irregularities responsible for 150 km radar echoes, not envisioned before. Unusually strong SNR and narrow spectral features of these echoes clearly indicate the role of sharp density gradients in the echoing process. Given the fact that Gadanki is located at magnetically low latitude, it is argued that these descending echoing layers are produced by interchange instability on the gradient of daytime descending ion layer formed by meridional wind shear associated with tidal/gravity waves quite similar to that observed during nighttime. The observations reported here are first of its kind illustrating the role of density gradient layers and are important in furthering our understanding on the puzzling 150 km echoing phenomenon.