Observations of trapped humidity layer and Kelvin-Helmholtz instability using UHF radar and GPS sonde

UHF radar observations at Gadanki (13.47°N, 79.18°E) and Vaisala type GPS sonde measurements of atmospheric thermodynamic parameters (temperature, pressure, relative humidity, wind speed, and wind direction) from Tirupati (13.63°N, 79.40°E) have shown two distinct features of the lower troposphere over this region. One of the features is the observation of trapped humidity layer just above the boundary layer. These trapped humidity layers and associated gradients are observed to contribute significantly to the UHF radar backscattering, especially at the edges of the humidity layer. The second phenomenon is the observation of a long-lasting Kelvin-Helmholtz instability (KHI), at the height of ∼3 km, which lasted for about ∼210 min. The UHF radar vertical beam echo power has shown the characteristic power bursts pattern associated with KHI. The characteristic wavelength and time period of KHI waves are found to be 3.78 km and 18.4 min, respectively. Thus these results illustrate two important processes in the lower tropical troposphere, which are very important in UHF radar backscattering.