Micro rain radar and radiometric measurements to unravel contrasting features of rain microstructure below and above the boundary layer

Abstract

Ka-band Micro rain Doppler radar is an effective tool to investigate the profiles of precipitation microstructure in terms of the raindrop size distribution (DSD). The DSD parameters that vary appreciably with height are indicative of the associated atmospheric phenomena. Hence the present investigation endeavors to put light on the underlying physical processes responsible for the evolution of varied rain microstructure profiles using micro rain radar (MRR), and radiometric measurements complemented with re-analysis outputs over an urban tropical location, Kolkata (22.57°N, 88.37°E), India. MRR unravels the prevalence of significant biases in the typical power law relationship (D m = aR ^b ) between rain rate (R) and mass-weighted mean drop diameter (D m ) along the rain height, especially during intense convective rain events, above the atmospheric boundary layer (ABL). Consequently, an alternative empirical relation appropriate to account for the R-D m variability above the ABL is proposed. Further, radiometric measurements and re-analysis outputs reveal that the presence of atmospheric instabilities coupled with wind shear impacts above the ABL contributes to the enhanced breakup of raindrops and the deviations in the usual R-D m relationship. Thus, the present study intends to highlight the applicability of ground-based radar measurements over the tropics to devise quantitative precipitation algorithms for reliable rain estimates.