Retrieval of mixed layer height (MLH) from lidar using analytical methods and estimation of MLH growth rates over a tropical site Gadanki

Abstract

A single channel elastic-backscatter lidar system was developed in-house at National Atmospheric Research Laboratory, an institution under Department of Space and Government of India, for studies on boundary layer dynamics during convective periods. The developed lidar system operates at the second harmonic wavelength of Nd: YAG laser and uses biaxial configuration. The lidar system utilizes a mini PMT for detecting laser returns from the atmosphere and operates in the analogue mode of data acquisition. The analogue recorder operates at 20 MHz sampling and uses a 12 bit A to D converter. The lidar system capable to operate at a maximum vertical resolution 7.5 m and 1-sec time sampling. However, in the present study, the lidar was operated with 30 m vertical resolution and 30-sec time sampling to understand the boundary layer dynamics during convective periods. The lidar measurements conducted between January and March 2014 were used in the present study. The laser backscatters obtained at 532 nm wavelength were corrected for noise and range before application of above mentioned analytical methods. This study presents evaluation of mixed layer height (MLH) from lidar using different analytical methods such as gradient, variance and wavelet techniques and presentation of inter-comparison between methods to achieve suitable method for assessment of MLH. The estimated MLH is then compared with the simultaneous radiosonde observations and empirical model values. We computed the MLH growth rates and observed that a significant enhancement was seen during the transition from winter to pre-monsoon period which could be attributed to increased convective activity over the tropical site. We present the lidar measurements and discuss the MLH retrieval and growth rates over Gadanki using lidar measurements.