Improving Microphysical Parameterization with Ground-Based Disdrometer Observations – A Squall-Line Case Study

A trial aiming at improving simulated precipitation in a squall line case is conducted based on a modified two-moment bulk microphysics scheme in WRF. The shape parameter of the gamma raindrop size distribution (RSD) is diagnosed in this modified scheme according to two empirical relations. One of the relations is obtained locally in Shandong in this squall line case and derived from the ground disdrometer. Simulation using the local diagnosed relation performs the best in terms of precipitation intensity and distribution compared against observations, though all the runs using different shape parameters show relatively large deviations from the real data. The modification of RSD leads to the change of rain microphysics, which affects the rainfall rate directly and subsequently the evolution of surface cold pool. Development of cold pool is found to influence the precipitation distribution and suppress the background cyclone intensification. These changes lead to interactions between the microphysics, cold pool, and dynamics, which finally influence the precipitation. Future work may focus on a more complete description of the RSD based on both airborne in-situ measurements and the ground-based observations as the disdrometer data is ground-based and large uncertainties exist when the disdrometer-derived RSD relationships are applied aloft.