First Triple‐Frequency Retrievals of Binned Raindrop Size Distributions

Abstract Our understanding of raindrop size distributions (DSDs) aloft is largely limited, owing to a scarcity of effective measurements. In this study, a two‐step optimal estimation technique is developed for retrieving binned DSDs based on a newly developed vertically‐pointing triple‐frequency radar system. In the first step, we employ the Tridon and Battaglia (2015, https://doi.org/10.1002/2014jd023023 ) approach for retrieving the DSD shape using Ka‐ and W‐band radar Doppler spectra. In the second step, we propose the synergetic use of C‐band radar (negligible attenuation) and W‐band radar (significant attenuation) for the retrieval of DSD number concentrations, making it a fully radar‐based technique. We applied this approach to a Mei‐yu frontal rainfall event in Eastern China. Validation against ground‐based OTT Parsivel 2 disdrometer observations quantitatively shows good agreement. Beyond traditional disdrometer observations, our radar retrieval captures the first view of binned DSD variations in Meiyu front rainfall.