Cloud Seedability Study with a Dual-Model System

AbstractIn this research, a novel dual-model system, one-dimensional stratiform cold cloud model (1DSC) coupled to Weather Research and Forecast (WRF) model (WRF-IDSC for short), was employed to investigate the effects of cloud seeding by silver iodide (Agl) on rain enhancement. Driven by changing environmental conditions extracted from the WRF model, WRF-IDSC could be used to assess the cloud seeding effects quantitatively. The employment of WRF-IDSC, in place of a one-dimensional two-moment cloud seeding model applied to a three-dimensional mesoscale cloud-resolving model, was found to result in massive reduction of computational resources. Numerical experiments with WRF-IDSC were conducted for a real stratiform precipitation event observed on 4–5 July 2004, in Northeast China. A good agreement between the observed and modeled cloud system ensured the ability of WRF-IDSC to simulate the observed precipitation process efficiently. Sensitivity tests were performed with different seeding times, locations, and amounts. Experimental results showed that the optimum seeding effect (defined as the percentage of rain enhancement or rain enhancement rate) could be achieved through proper seeding at locations of maximum cloud water content when the updraft was strong. The optimum seeding effect was found to increase by 5.61% when the cloud was seeded at 5.5 km above ground level around 2300 UTC 4 July 2004, with the maximum Agl mixing ratio (Xs) equaling 15 ng kg-1. On the other hand, for an overseeded cloud, a significant reduction occurred in the accumulated precipitation (12.42%) as Xsreached 100 ng kg-1. This study demonstrates the potential of WRFIDSC in determining the optimal Agl seeding strategy in practical operations of precipitation enhancement.