中国气象学会气象青年科技交流会暨2022年青年科学家论坛

The mean terminal velocities of different types of hydrometeors play an important role in cloud dynamical and microphysical processes. In this study, numerical simulations of a tropical deep convection from WRF model coupled with spectral bin microphysics was used to investigate the relationships between mean terminal velocity and volume mean diameter of different hydrometeors (i.e., cloud droplet, rain drop, ice crystal, snow, and graupel) as well as how they change with different background aerosol concentrations. The results showed a positive correlation between either the mass-weighted mean terminal velocity (V_m) or the number-weighted mean terminal velocity (V_n) and the volume-mean diameter (D_v), with correlation coefficient greater than 0.8. The amplitude of V_m and V_n are contributed mostly by large and small size of hydrometeors, respectively, hence the values of V_m are greater than that of V_n. The number concentrations of both large and small size of hydrometeors increase with enhanced aerosol loading, resulting in increment of V_m and decrement of V_n respectively. The parameterizations of V_m (V_n) have been established under different aerosol conditions. The parameterized V_m (V_n) was then compared with default values used in the model when a fixed shape parameter of gamma distribution used in the bulk microphysics theoretically, which suggesting smaller V_m while larger V_n values from the parameterizations. Moreover, the proposed parameterizations are further applied to the Morrison microphysical scheme in WRF model for simulation of a convective cloud. Changes in V_m and V_n as mentioned above directly affect the sedimentation process of precipitating hydrometors, such as raindrop, snow and graupel, which lead to increased (decreased) mass (number) concentration of hydrometeors. Changes in the parameterization of the mean terminal velocity lead to different vertical structure of hydrometeors.

对流云;气溶胶;参数化;下落末速度