Microphysical Characteristics Of Stratiform Clouds With Embedded Convectionderived From Aircraft Observation And Numerical Simulation In Northern China

Ice crystal habits, distribution and growth process in two cases of stratiform clouds with embedded convection on18April2009and1st May2009are analyzed with data observed during the Beijing Cloud Experiment (BCE), and then, to verify the cloud microphysical scheme and ability in simulating cloud microphysics, thecloud microphysics and precipitation characteristics intwo cases simulated by WRF modelwere compared with data observed during the BCE. The results show that:Ice crystal habits in clouds with temperature between0--16℃were predominantly plate, needle-column, capped-column, dendrite and irregular. Ice crystal habits were affected by the cloud top temperature(CTT) and were different with the change of CTT, plate and needle-columns were predominant habits as CTT warmer than-8℃, but dendritic and capped-column crystals were observed just as CTT colder than-13℃and-18℃respectively. At the same time,ice crystal habits were also affected by their locations in cloud. A mixture of several ice crystal habits always be recorded in different clouds. But the ice crystal habits recorded in embedded convections contained more dendrites and had a heavier riming degree, and the ice crystal recorded in stratiform clouds contained more hexagonal plate crystals. Above the melting layer, ice particle grew mainly by deposition,riming and aggregation process,the riming process became more intense in lower cloud layer due to the increase of supercooled liquid water content. The broaden rate of Particle size distributions(PSDs) is obviously different between embedded convections and stratiform cloudsin the vertical direction, at levels4.8-4.2km(-11.6—-8℃), the PSDs broaden rate in embedded convections is3mm km-1,smaller than3.67mm km-1in stratiform clouds, but at levels4.2-3.6km(-8--5℃), the PSDs broaden rate in embedded convections is6.67mm km-1,which was almost three times as big as2.33mm km-1in stratiform clouds, which is mainly due to that embedded convections had more supercooled liquid water than stratiform cloudsat levels4.2-3.6km.The simulated results show that the distributions of radar echo and precipitation simulated by WRF model are in good agreement with observations. The simulated vertical distribution of Liquid Water Content (LWC) is consistent with aircraft measurements, especialy at middle and low layer of cloud, although the simulated LWC at high layer (-8--16℃) flight path has some errors with observation due to the location error of embedded convection simulated by model. The Ice Water Content (IWC) at high layer simulated by model is higher than observation due to that the simulated riming process is stronger at this layer, and aggregation process occurred at higher layer, so it needs an improvement at production processes of snow. Vertical distributions of water content at middle and low layer (most of cloud water is LWC) are simulated correctly,including the melting layer.For the case of18April, at-8℃layer, both the intercept and slope of Particle size distributions(PSDs) simulated by model are lower than observations due to simulated snow mass concentration is higher than observed. At-5℃layer, both simulated intercept and slope are consistent with observations. At3℃layer, the simulated slope is consistent with observation, but the simulated intercept is higher than observation due to concentration of small particles is decreasing in cloud, that suggest the parameter of spectrum shape shoud change with height in cloud. For the case of1st May, the comparation results were similar with the case of18April, the simulated slope of PSDs at high layer is smaller than observation due to more snow content were simulated at high layer. With the decrease of height, the PSDs changed from MP distribution to Gamma distribution. In addition, the simulated results at embedded convection were closer to observation, and at stratiform region were higher than observation. In addition, the simulated broadening rate of PSDs in embedded convection and stratiform region both were smaller than the observed results. Two numerical experiments suggest that there is a problem with the parameter of ice process in cloud physical scheme in WRF model, especialy at riming process and collision process. At the same time, the parameter of spectrum shape of PSDs should change with height in cloud.