Effectiveness Evaluation of Dual-Aircraft Collaborative Rain-Enhancement Operations in Danjiangkou by Using the CMA-CPEFS Numerical Model

This study investigates the cloud and precipitation responses to dual-aircraft collaborative rain-enhancement operations conducted on June 4, 2023, in Danjiangkou, Hubei Province, China. Utilizing the CMA-CPEFS numerical model to simulate the actual seeding processes, we analyze the mechanistic changes in macro- and microphysical characteristics of clouds and precipitation following the joint operations and evaluate their effectiveness. The model successfully reproduced key macroscopic cloud and precipitation features, with simulations indicating favorable cold-cloud seeding conditions in the target cloud system. Quantitative diagnostic results reveal: (1) The seeding operations influenced radar reflectivity patterns, with enhanced echo intensities in the affected regions, consistent with observational radar trends. (2) Both aircraft sorties generated measurable rain enhancement, with the second operation exhibiting stronger seeding efficiency than the first. (3) Increased surface precipitation primarily originated from graupel growth. Post-seeding, ice crystals and snow particles significantly increased in the cold-cloud layer, driving graupel accumulation in lower cold-cloud regions. This enhanced graupel melting into raindrops in the warm layer and intensified cloud-rain collision-coalescence processes. (4) The operations achieved localized rainfall enhancement, with a maximum 1.5 mm precipitation increase over 10 hours in the core impact zone. The affected area exhibited an average rainfall increase rate of 2.1%, yielding a net precipitation gain of approximately 78,000 metric tons, while downstream regions experienced extensive rainfall expansion.