Impact Of Black Carbon Aerosol Acting As Ice Nuclei On The Development Of Cumulus Clouds Over The North China Plain

Cumulus clouds that consist of mixed-phase particles,are ubiquitous in the Earth's low and middle troposphere where clouds are integral to hydrological cycle,and have an essential impact on Earth's climate.Changes in the liquid or ice phases composition in such clouds may significantly affect the radiative balance of the earth atmosphere system.The cloud-phase composition in mixed-phase clouds is complicatedly affected by the atmospheric aerosols which are serving as cloud condensation nuclei?CCN?and ice nuclei?IN?aerosols.Aerosol particles formed from natural and anthropogenic sources can influence the global climate directly by scattering and absorption of solar radiation,and indirectly by affecting cloud properties,precipitation.Both CCN and IN can modify the optical properties and lifetime of clouds,and the IN tend to be very rare in atmosphere with comparison to the CCN.However,IN are presumed to be vital to the initiation of ice in mixed-phase clouds,and an essential first step in precipitation formation.The number of concentration of IN as well as temperature and supersaturation required to“activate”IN are considered as key information for the understanding of primary ice formation in clouds.In the present study,the effect of ice nuclei?IN?on the development of cumulus clouds over the North China Plain has been investigated using a cloud-resolving weather research and forecasting model with a two-moment bulk microphysical scheme including aerosol effects on cloud condensation nuclei?CCN?and IN.A convective cumulus cloud event occurring on 24 August 2014 is simulated,and the sounding profile reveal a moderate instability with a convective available potential energy?CAPE?of 651 J kg^-1.A set of black carbon?BC?profiles is used in the simulations,with the surface number concentration varying from 2 to 2000 cm^-3 and the mass concentration varying from 0.006 to 5.6?g cm^-3.The simulation results show that in the LCCN condition,the ice number concentration is higher than the other two cases?HCCN and MCCN?when BC number concentration is very low;Under the HCCN condition,the ice number concentration increases with the increases of BC more sharply than in the LCCN cases.Increasing IN concentrations slightly enhances the cloud core updraft and maximum updraft and intensifies the convection under various CCN situations.Ice,snow and graupel number concentrations increase with the increases of BC.The core updraft of the cloud intensified with the increases of BC,because the more condensation and sublimation processes the more latent heat can be released,it can be further heated the atmosphere.The precipitation increases steadily with IN concentrations,caused by the enhanced mix-phased process due to increasing IN,but it is not sensitive to the IN variation.The precipitation enhancement is less than 1%with the IN concentration increasing from 0.006 to 5.6?g cm^-3.Therefore,the IN generally do not play a dominant role in the development of cumulus clouds during summertime.