Study On The Microphysical Properties Of Clouds And Its Evolution In Precipitation Process

Based on the finely resolved CloudSat data products,the microphysical characteristics of stratocumulus clouds and deep convective clouds over Eastern China are investigated in this study.Cloud microphysical mechanism evolutions during the development of stratocumulus clouds and deep convective clouds which are divided based on the magnitude of liquid water path and ice water path,respectively.Furthermore,the cloud parameters of typical precipitation cases simulated by different microphysics schemes of WRF mode were tested with CloudSat data,and then the better simulation results were selected to study the evolution of cloud microphysical characteristics before and after precipitation peak,so as to deeply understand the cloud lifetime and precipitation generation mechanism,and provide novel ideas to the simulation study of typical precipitation cases.From the analyses we conclude that the quantity value of liquid water path in precipitating stratocumulus clouds is greater than that in the non-precipitating stratocumulus clouds.In non-precipitating stratocumulus clouds,condensation process is the primary mechanism for hydrometeor particle growth,but this mechanism is inversely proportional to the particle radius,therefore,it is difficult for cloud droplets to form drizzle or raindrops simply through condensational growth.In the vigorous developmental stage of non-precipitating stratocumulus clouds,the relatively feebler coalescence process appeares in the upper layers of clouds.The coalescence process becomes evident in precipitating stratocumulus clouds.When cloud liquid water path is less than 500 g·m^-2,cloud droplets grow in size continuously by the coalescence process tamhsi atdnhd el5ey0 fp0a al rlgt t·ho rfm ot-uh2ge,h c ttlhhoeeu dec,nottaihlreee s tccrleaonnucsidet i loparnyo efcrr.e ossWm hocelcnoc uucrdls o d urmdo olpisltqeltuysi dit now rtaahtieenr duprpaotpphes r b i lse acymoeomrsset.s aIlcnat ri tgvheeer,and the maximum values of cloud liquid water content,liquid number concentration and liquid effective radius appear in this level.With the development of deep convective clouds,the cloud liquid water content decrease and the cloud ice water content increase,the cloud droplets are constantly transformed into rain drops and ice crystal particles.With the increases of cloud ice water path,the heights witch precipitation generate increased.The maximum values of ice particles and cloud water content in deep convective cloud are within 4.0-8.0 km in clouds.The elevation layer is a mixed layer,where supercooled cloud water,water vapor and cloud ice existed together,the conversion among cloud water,rain water and ice are the most active through Bergeron process,coagulation and riming growth,and the rainfall intensity reaches its maximum.The difference in cloud microphysical properties of stratocumulus clouds or deep convective clouds between sea and land can be accounted for the difference in updraft strength,aerosol concentration and moisture.WRF model is employed in this paper,and five microphysical schemes are selected to simulate the rainfall process associated with typhoon Bolaven in Liaoning province.The CloudSat observation results are used to test the vertical distribution of cloud fraction and ice water content simulated in different schemes,and it is found that the simulation results of Purdue Lin are better than those of the other four schemes,but its simulation of ice cloud water content is relatively low.Lastly,based on the simulation results of Purdue Lin scheme,all grid points are synthesized with the precipitation peak time as the standard,and study the evolution of cloud microphysical characteristics before and after the precipitation peak time.It is found that,the evolutions of cloud microphysical properties are closely related to the evolution of the rising motion intensity in the cloud.At four hours before the P_max time,a great quantity of water vapor is transported to high altitude result from the strongest rising motion,the water vapor freeze and generate snow through Bergeron process,snow can constantly coagulate and produce graupel.And then graupel melt into rain water,which subsequently contributes to the surface rainfall before the precipitation peak time.As the precipitation rate first increases and then decreases,the distribution height of maximum value center of cloud water gradually decreases.With the increase in cloud water content,the coagulation of rain water to cloud water is enhanced,which became the main source of precipitation after the precipitation peak.Additionally,the accretion of cloud water by rain is the main cloud microphysical process which affects the intensity of surface precipitation.