The Impact Of Cloud Condensation Nuclei On Different Summer Precipitation Process In Nanjing:Numerical Simulation

The research showed that the aerosol emitted due to the rapid urbanization in China can act as the cloud condensate nuclei(CCN),which will affect the occurrence and development of cloud and precipitation.In order to explore the relationship between CCN and precipitation and to distinguish the difference between CCN and precipitation in different environmental fields,WRF3.8.1 with the improved Thompson cloud microphysical parameterization scheme was used to simulate the two cases of systematic precipitation and local severe convective precipitation,to discuss the influence of CCN on the precipitation of different environmental fields in Nanjing.Firstly,different microphysical parameterization schemes were used to simulate the systematic precipitation case at the beginning of June 2014 in Nanjing to select the appropriate parameterization scheme.The effects of CCN concentrations on this case were compared by two numerical experiments which represent high and low CCN concentrations respectively.The results show that:the improved Thompson microphysics scheme had a certain ability to reproduce the precipitation.The higher concentration of CCN was beneficial to the increase of total accumulated precipitation and the expansion of precipitation.The intensity of the strong precipitation center increases with the increase of CCN concentration,but for the weak precipitation center,the increase of CCN concentration has the opposite effect.The increase of CCN concentration will inhibit the conversion of cloud to rain and the development of warm cloud process.But it will promote the development of cold cloud process by accelerating the production of snow and graupel.Secondly,the Thompson scheme with three CCN concentrations(high,normal,low)was used to simulate the local severe convective process in July 6,2016(GMT).The results showed that surface accumulated precipitation and warm cloud process were weakened with the increase of CCN concentration.The ice crystal formation was inhibited by the high CCN concentration,and snow and graupel concentration were decreased by the warmer ambient temperature.The graupel disappeared was delayed as the result of the maintenance of supercooled cloud water at the the middle troposphere.Finally,the responses of precipitation in different environmental fields to the change of CCN concentration were compared.The Low(high)cloud amounts could indirectly reflect the development of warm(cold)cloud process,and the cloud amounts also had a good relationship with the surface precipitation.The increase of CCN concentration weakened the evaporation process,inhibited the convergence and uplift around the ground cold pool,and produced the negative feedback on the warm cloud process.In the polluted systematic precipitation,weaker vertical motion was propitious to more graupel and snow,as well as more latent heat released which strengthened the updraft.The ground cold pool was enhanced by the melting of snow and graupel during falling,and the convergence and updraft before the cold pool were promoted.Thus,CCN increasing resulted in the positive feedbacks on the cold cloud process.