VHF radar observations of mesospheric echoes and their relationship with thermal structure over Gadanki (13.5°N, 79.2°E)

Abstract

There have been several reports on the comparison of daytime mesospheric echoes and their relationship with nighttime thermal structure. In the present work, a few cases are presented in which mesospheric echoes, observed with the MST radar at Gadanki (13.5°N, 79.2°E) during January-February 2011, are compared with temperature information obtained by Sounding of Atmosphere by Broadband Emission Radiometry (SABER) instrument onboard Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics (TIMED) satellite, when there is an overpass near Gadanki close to the time when the echoes are observed. It is found that the mesospheric echoes occur at heights where temperature is minimum or tends to be minimum as compared to the temperature at adjacent heights. The temperature lapse rate decreases below and increases above the height of maximum echoes. This relationship is consistently observed in all the cases considered in the present work. It appears that echoes arise due to change in the refractive index associated with electron density fluctuations caused probably by wave breaking and subsequent turbulence, which could be inferred from the minimum temperature (dynamical cooling) at the height of wave breaking.