Effects Of Aerosols On Different Types Of Cloud Precipitation Systems During Autumn And Winter In North China

North China is an important economic,political,and cultural center in China with a dense population,developed economy,and high urbanization.Although the average precipitation in this region is less during autumn and winter due to the weakening of the East Asian monsoon,extreme precipitation events occasionally occur,seriously threatening transportation,industrial and agricultural production,and the safety of people’s lives and property.Aerosol emitted from anthropogenic and natural activities have a significant impact on cloud precipitation systems and the formation and development of extreme rain and snow events in autumn and winter.Currently,there have been many studies on aerosol-cloud-precipitation interactions in North China in summer,but the impact of aerosols on cloud-precipitation systems during autumn and winter is comparatively rare,and the extent of the impact and associated mechanisms have not been fully clarified.Therefore,this paper analyzed the relationship between aerosols and the macro and micro characteristics of convective cloud precipitation systems and stratiform cloud precipitation systems during autumn and winter in North China from 2014 to 2021 based on Global Precipitation Measurement-Dual-Frequency Precipitation Radar(GPM-DPR)inversion data and The Modern-Era Retrospective Analysis for Research and Applications,Version 2(MERRA-2)global reanalysis data,and the role of different meteorological conditions was investigated.On this basis,the Weather Research and Forecasting model coupled with Chemistry(WRF-Chem)was applied to simulate two typical precipitation processes and analyze the influence mechanism of aerosols on the convective cloud precipitation system and stratiform cloud precipitation system in North China during autumn and winter.The main findings are as follows.(1)The relationship between aerosols and the convective cloud precipitation system in North China during autumn and winter was studied.There was a significant positive correlation between the Aerosol optical depth(AOD)and the convective precipitation rate during autumn and winter in North China.Convective cloud precipitation systems tended to have higher rain top height,more but smaller precipitation particles,increased latent heat release,and enhanced radar reflectivity in the polluted state.A stronger positive correlation was exhibited between AOD and convective precipitation rate when the atmosphere has higher precipitable water,lower vertical wind shear,or weaker atmospheric stability.However,the changes in the above meteorological factors did not alter the positive correlation between AOD and convective precipitation rate.(2)Differences in the relationship between aerosols with stratiform cloud precipitation and convective cloud precipitation during autumn and winter in North China were found.Compared with convective cloud precipitation systems,there was no significant correlation between AOD and the precipitation rate of stratiform cloud precipitation during autumn and winter in North China.The differences in macro and micro characteristics of stratiform cloud precipitation systems,such as precipitation rate,rain top height,radar reflectivity,precipitation particle spectrum distribution,and latent heating rate,were imperceptible between polluted and clean states.The reason may be that stratiform cloud precipitation systems were more susceptible to atmospheric water vapor conditions and vertical upward motion than convective cloud precipitation systems.(3)The mechanism of promoting the effect of aerosol on the convective cloud precipitation system in autumn in North China was revealed.More aerosols in the polluted state promoted the condensation of water vapor,forming more cloud droplets but with a smaller effective radius,and the auto-conversion process of cloud droplets to rain was consequently restricted.However,after the raindrops produced by the slow auto-conversion process,they can accrete cloud droplets and thus obtain a larger effective radius,leading to a higher rain mixing ratio.The increase of aerosols can promote snow deposition,and the large number of cloud droplets suspended in the atmosphere accelerated the riming growth of snow,forming more snow particles with a larger effective radius,and thus the mixing ratio of snow increased.The higher mixing ratio of cloud water,rain,and snow led to more and heavier precipitation reaching the surface.The microphysical processes such as condensation,deposition,and riming released large amounts of latent heat,further promoting the atmosphere’s vertical upward motion and the development of convective systems.(4)The limited impacts of aerosols on winter stratiform cloud precipitation systems in North China were discovered.Aerosols had a weak inhibitory effect on stratiform precipitation in winter in North China.This was mainly because most of the aerosols in the stratiform cloud precipitation system accumulated below 2 km and were hardly transported by the relatively weak vertical motion within the system to the height where the ice-phase process occurred.Therefore,although the increase of aerosols promoted the condensation of water vapor below 2 km,this process also consumed some of the water vapor used for ice phase processes such as deposition and freezing,inhibiting the development of ice phase processes.The increase in aerosols also restrained the auto-conversion of cloud droplets to rain and the formation of warm rain.Less rain,snow,and ice eventually reduced precipitation rate and cumulative precipitation under pollution conditions.In this study,the different effects of aerosols on convective and stratiform cloud precipitation in North China during autumn and winter and the related physical mechanisms were elucidated.The relevant results contribute to an in-depth understanding of aerosol-cloudprecipitation interactions in North China and provide support to improve the accuracy of regional meteorological forecasts and the response capability to extreme weather.