Drop Size Distribution from Laboratory Experiments Based on Single-Drop Fragmentation and Comparison with Aerial In Situ Measurements

Abstract Laboratory experiments and theoretical modeling are conducted to determine the raindrop size distribution (DSD) resulting from distinct fragmentation processes under various upward airstreams. Since weather radar echoes are proportional to the sixth power of the average droplet diameter, understanding the fragmentation mechanisms that lead to different breakup sizes is crucial for accurate rainfall predictions. We utilize a two-parameter gamma distribution for theoretical modeling and estimate the average droplet diameter from the theoretically obtained characteristic sizes, often treated as assumed input parameters for different rain conditions in rainfall modeling. Our experimental and theoretical findings demonstrate a close agreement with the DSD predicted by the Marshall and Palmer relationship for steady rain conditions. Additionally, in situ DSD measurements at different altitudes were obtained through research flights equipped with advanced sensors, further validating our rainfall model. This study underscores the effectiveness of laboratory-scale experiments and the critical importance of accurately characterizing DSD to enhance rainfall predictions. Significance Statement The present study advances the fundamental understanding of rainfall prediction by integrating laboratory experiments, theoretical modeling, and in situ measurements. We employ shadowgraph and machine learning–based in-line holography techniques, supported by theoretical modeling, to determine the DSD resulting from raindrop fragmentation. Using a two-parameter gamma distribution, we estimate average droplet diameters, critical for interpreting radar echoes and refining rainfall models. Our results align closely with the Marshall and Palmer relationship for steady rain, emphasizing the importance of precise DSD characterization. Furthermore, precipitation measurements at varying altitudes, obtained from research flights equipped with advanced sensors, validate the laboratory results, providing key insights into atmospheric processes and enhancing the accuracy of rainfall estimation.