Climatological Characteristics Of Hydrometeors In Precipitating Clouds Over Eastern China And Their Relationship With Precipitation

This study analyzes the long-term characteristics of four hydrometeors（cloud water,rain,cloud ice,and snow）and their quantitative relationship with surface precipitation in eastern China（South China,Jianghuai,and North China）from May to August in 1979-2020 using the fifth-generation ECMWF Re Analysis（ERA5）.Moreover,the impacts of hydrometeors and latent heat of microphysical phase change on precipitation intensity during a heavy rainfall event in Zhengzhou on July 20,2021are investigated through the Weather Research and Forecasting（WRF）simulations.The climatological distributions of hydrometeors reveal that cloud water path decreases significantly from south to north owing to the large-scale circulation and water vapor distribution,with the maximum value of 180 g m^-2 in South China and only half in North China.Areas with high rain water path(>50 g m^-2)are located in southwestern South China,southeastern Jianghuai and Taiwan island,and the distribution pattern is consistent with that of surface precipitation.Cloud water path and precipitation have a positive correlation,but when the precipitation intensity increases to 15 mm h^-1,the cloud water path no longer increase with rain intensity.A clear linear relationship between the rain water path and precipitation intensity exists and its slope value is the maximum(5.68 h^-1)in South China,implying the highest conversion rate from rain water to precipitation over there.When the precipitation rate exceeds 15mm h^-1,the ice-phase hydrometeor contents in South China become the largest among the three regions,indicating the cold rain process is crucial to the heavy rainfall.In the regional mean diurnal variation,the peaks of cloud water path commonly appear 2-3 h ahead of precipitation,while the peaks of ice-phase particles occur 2 h and 1 h behind the afternoon precipitation in South China and Jianghuai,which is mainly attributed to the different upward velocity and water vapor convergence in the middle-upper troposphere.In addition,the 3D precipitation diagnostic equation can be used to accurately analyze the relationship between precipitation and water vapor and hydrometeors.Precipitation intensity is primarily determined by the moisture-related processes,including local water vapor change,water vapor flux divergence,and surface evaporation.While the contribution of hydrometeor-related processes（local change and flux divergence of hydrometeors）to monthly average precipitation is generally between-5%and 5%,we find that it can jointly modulate the location of heavy rainfall.The simulation results of an extreme precipitation in Zhengzhou indicate that the water vapor flux convergence is the key to generating heavy precipitation;however,the hydrometeor-related processes cannot be ignored,particularly at the beginning of rainfall,where their contribution can be up to 30%-50%.The liquid-phase hydrometeors（cloud water and rain water）always play a positive role in increasing precipitation during the rainfall process,while the ice-phase hydrometeors turns to a negative contribution in the middle and late stages of precipitation because of their divergence at 4-8 km height.The lower-level atmosphere serves as a heat source,and most of the latent heat released by phase change is transported to the upper-level atmosphere via the updraft,and then diverging through the horizontal wind,weakening the heating effect in the upper atmosphere.In addition,the latent heat process of hydrometeor phase change significantly affects the buoyant distribution and vertical velocity of the atmosphere.The condensation latent heat of cloud water is the largest along with the widest coverage,and the occurrence height of deposition latent heat is the highest（which can exceed 10km）.The center position of phase change latent heat is close to that of the vertical velocity and buoyancy,but their relationship in the lower layer is complex.In this paper,the long-term spatial distribution characteristics of four hydrometeors and their possible influences on summer precipitation evolution in eastern China are obtained for the first time.The effects of hydrometeor-related processes and microphysical phase-change latent heat on the precipitation intensity in a heavy precipitation case are explored.The results can refine the thermodynamic structure in convective clouds,and are helpful for understanding the impact of hydrometeors on precipitation mechanism from a cloud-scale perspective.