Impacts Of Aerosol On Cloud And Precipitation In North China

Atmospheric aerosol has important effects on regional and global weather and climate through aerosol-radiation interactions(ARI)and aerosol-cloud interactions(ACI).The dense population,intense human activities,and various types of anthropogenic aerosol emissions,together with the long-distance transport of dust aerosol from source areas such as the Taklamakan Desert and the Gobi Desert,have contributed complex aerosol properties over North China.Aerosol can act as cloud condensation nuclei/ice nuclei to influence cloud microphysical processes,thereby affecting precipitation.Therefore,studying the impacts of aerosol on cloud and precipitation processes in North China is important for understanding the weather and climate change in this region.Using station observations,multi-sourced satellite sounding,multiple reanalysis data,and numerical models,this study systematically investigates the distribution features of aerosols in North China,explores the variation characteristics and the influence mechanism of dust weather frequency in North China,and quantifies the effects of anthropogenic and dust aerosols on cloud and precipitation.This study could provide a scientific basis for understanding the weather and climate change in North China.Some findings are as follows:(1)The spatial and temporal distributions and variation of aerosols in North China are revealed.The aerosol types in North China are mainly anthropogenic sulfate and black carbon aerosols,among which sulfate aerosols are higher in summer,black carbon aerosols are higher in winter,and organic carbon aerosols are less in North China.Overall,anthropogenic aerosols in North China show a distribution feature of higher values in the south and lower in the north,and their average optical depth is slightly higher than the average value for the whole China,and they show a significant increasing trend during 1980-2021,but decrease after2013.Dust aerosols are mainly concentrated in desert areas and less in North China,and they increase significantly in Northwest China and decrease in North China during 1980-2021,with the most significant decreasing trend in summer in North China.(2)The characteristics and a mechanism of the changes in dust weather frequency in North China are found.It was found that the dust weather frequency(DWF)in North China decreases significantly during 1979-2021,among which the DWF in spring of 1982-2008 is mainly linked with the decrease of sea ice concentration in the Barents Sea(SICBS)in the previous winter,while it is significantly associated with the negative phase of Arctic Oscillation(AO)in the previous winter during 2009-2021 period.Due to the decreased SICBS in the preceding winter during 1982-2008,the surface adiabatic heating excites Rossby waves to spread southward and eastward,snow cover over Eurasia is decreased,which lead to the abnormal northerly wind in North China in the ensuing spring,causing frequent dust weather in this region.On the other hand,during 2009-2021,when the negative AO phase occurs in the preceding winter,the increased meridional temperature gradient at mid-latitudes tends to enhance westerly wind and cyclogenesis over North China,leading to more dust weather in the ensuing spring.Consequently,both the negative AO phase and decreased SICBS in the preceding winter cause the strong wind and dry soil in the dust source region,resulting in frequent occurrence of dust weather in North China in spring.(3)The ARI and ACI effects of anthropogenic aerosols and their contribution on different-grade precipitation in North China are quantified.In terms of the global-scale climate change,anthropogenic aerosols can intensify the drought in the East Asian subtropics.Based on the results of weather process study,anthropogenic aerosols have different effects on different-grade precipitation.The case study found that anthropogenic aerosols can increase the heavy precipitation(>1.04 mm/hour)by 70.96%,while it can suppress the moderate(0.41-1.04 mm/hour)and weak precipitation(<0.41 mm/hour)by 24.87% and 86.43%,respectively.For the heavy rainfall process,the ARI effect of anthropogenic aerosols can enhance the upward motion,increase the cloud water path and effective radius;however,the combined effects of ARI and ACI of anthropogenic aerosols can weaken the upward motion and reduce the ice water path during moderate and weak precipitation,which can suppress moderate and weak precipitation.(4)The enhancement of precipitation in North China by dust aerosols is clarified.Dust aerosols can serve as atmospheric ice nuclei due to their excellent ice-forming properties.The increase of dust aerosols can significantly increase the ice crystal number concentration at the upper troposphere.Due to the Bergeron process,the number concentration and effective radius of liquid cloud droplets in lower layer are reduced,and the supercooled water cloud slightly decrease.In the atmospheric layer where the ice crystal number concentration increases,the effective radius of ice particles decreases significantly,leading to a decrease in precipitation.On the other hand,a large amount of latent heat released by dust aerosols in the nucleation process can enhance the convective activity in cloud,with strengthened upward motion,higher cloud top height,reduced cloud top temperature,and increased ice water path,resulting in increased total precipitation by 1.78%.