Estimation of Layer-Averaged Rain Rate From Zenith Pointing Ka-Band Radar Measurements Using Attenuation Method

Traditionally, Ka-band radars are opted for cloud studies as the radar signal at this frequency gets attenuated during rainy condition. In this work, an attenuation-based method is used to estimate the layer-averaged rain rate from vertically pointing Ka-band radar deployed at Mandhardev (18.04 °N, 73.87 °E, ~1.3 km AMSL), a remote station in the hill-top of Western Ghats, India. At Ka-band, the rain rate retrieval depends on the linear relation between specific attenuation coefficient and rain rate. The specific attenuation coefficient is calculated from T-matrix scattering simulation performed at Ka-band frequency using the Joss-Waldvogel disdrometer (JWD) raindrop data. The radar retrieved rain rates for 0.5- and 1-km rain layer depths are evaluated with the collocated JWD rain rate measurements. The rain rates retrieved from 1-km rain layer depth shows higher correlation, 0.75, and small bias, 2.36 mm h^-1, compared to 0.72 and 3.65 mm h^-1, respectively, for 0.5-km rain layer depth retrievals. Further, the vertical profiles of rain rate are constructed for both 0.5- and 1-km rain layer depths. It is observed that the retrieval error decreases, with an increase in rain rates. The good comparison of the rain rate between the radar and the JWD validates the possibility of using cloud radar observations for the retrieval of the rain rate.