Hydrometeor Budget of the Meiyu Frontal Rainstorms Associated With Two Different Atmospheric Circulation Patterns

Characteristics of hydrometeor budget and the microphysical processes responsible for heavy precipitation are studied based on the WRF model simulations of two representative Meiyu frontal rainstorms that are associated with two distinct atmospheric circulation patterns. Case 1 is characterized by the coupling of the Eastward Propagating Mesoscale Vortex (EPMV) and Meiyu front, while Case 2 is dominated by the interaction between the Low-Level Wind Shear (LLWS) and Meiyu front. The temporal and spatial characteristics of the hydrometeor budget are validated against observations and assimilation products including those obtained during the 2018 Integrative Monsoon Frontal Rainfall Experiment (IMFRE) campaign and discussed in the context of contrasting the precipitation intensification and dissipation stage. Specifically, the ice-dependent cloud processes, rather than the liquid-dependent cloud processes, are predominantly responsible for the variation of precipitation. These terms include the deposition from water vapor to the ice phase hydrometeors, the accretion from cloud liquid water to the ice phase hydrometeors in the upper troposphere, and the melting of the ice phase hydrometeors into raindrops in the mid-lower troposphere. Then three major ice cloud conversion pathways and two minor warm cloud conversion pathways for the formation of raindrops are extracted from the overall microphysical processes active in both Case 1 and Case 2. One of the key findings is that ice-dependent cloud processes are significantly more active in the case characterized by the coupling of EPMV and Meiyu front, and this difference is at least partly explained by the differences in dynamical and thermodynamic conditions dominated by the circulation patterns.