Reflectivity-Rain Rate Relationship for Orographic Rainfall at Mahabaleshwar Over the Indian Western Ghats

Abstract

The reflectivity (Z)-rain rate (R) relationship is crucial for describing the microphysical characteristics of precipitating clouds and plays a vital role in assessing the performance of polarimetric Doppler radar and rain gauge measurements. For the first-time, the power-law Z-R relationship (\(Z{=aR}^{b}\)) is determined for stratiform and convective rainfall during the pre-monsoon, monsoon, and post-monsoon seasons at Mahabaleshwar, a tropical station in the Western Ghats, using the in-situ Joss-Waldvogel Disdrometer (JWD) measurements from 2014 to 2019 at the High-Altitude Cloud Physics Laboratory (HACPL: 17.56 ^oN, 73.4 ^oE; ~ 1400 m above MSL). The proportion of convective precipitation to the total precipitation during the pre-monsoon, monsoon, and post-monsoon seasons are ~ 42%, 53%, and 27%, respectively. The Z-R equation was derived using the linear regression method for different seasons and rain types. Pearson correlation coefficient between Z and R is high (r > 0.90) in all three seasons. The analysis shows that derived Z-R equations overestimate the value of Z for the rain events having R < 10 mm/hr and underestimate for R ≥ 10 mm/hr. Notably, the Z-R equation for the Western Ghats differs from those reported for mid-latitude and oceanic regions, reflecting the strong influence of regional topography, season and rain microphysics on precipitation characteristics. The coefficients “a” and “b” of the derived Z-R equation show substantial variation with season and rain type in comparison to the earlier studies at Gadanki and Tirupati due to differences in local atmospheric dynamics and complex orographic effects. The region-specific Z-R relationship may improve the radar-based rainfall estimations and also our understanding for rain microphysics over the Western Ghats.