Microphysical Characteristics And Precipitation Formation Mechanism Of Stratiform Cloud With Embedded Convections In Eastern Taihang Mountain

The structure of a stable stratiform cloud with embedded convections in eastern Taihang mountain on 22 May 2017 is analyzed using aircraft and ground-based radar measurements,and the simulation by WRF model on this case is conducted and discussed.Also,the orographic effects of Taihang mountain on cloud and precipitation are preliminarily investigated.The findings are as follows:High concentration of large-size ice particles was found to exist in the upper part of the cloud,and the growth process of these ice particles varied in different areas when falling to the lower levels.In embedded convections ice particles grew mainly by aggregation and riming processes due to the existence of high supercooled liquid water content,and in clouds lack of supercooled liquid water their growth depended on the aggregation process.As a result,the large-size ice particles formed by aggregation were of lower density and less falling velocity,and they took longer time to fall through the 0?layer,so that more obvious melting phenomena were observed in these clouds than embedded convections.The convections embedded in stratiform clouds were generally located between 0?^-10??4⁶km?,with vertical and horizontal scales of about 2km,and maximum updraft velocity of5m s^-1.In embedded convections,the average liquid water content is about twice that of surrounding clouds,and the average concentration of small cloud particles is one order of magnitude higher than that of surrounding clouds,the concentration of large particles?diameter greater than 800?m?is higher too.The precipitation growth in embedded convections with high supercooled liquid water content took place through the“seeder-feeder”process,while clouds with low supercooled liquid water content did not follow this process.The simulations by WRF can well reproduce the movement and development of clouds and the structure of radar reflectivity,including the echo of embedded convection in the cross-sections,but the locations of convections slightly deviate from observations.Accumulated rainfall and hourly precipitation rates simulated matches well with that observed,but the time and intensity of maximum precipitation rates have some differences.The model can present the differences of vertical structures of clouds at different locations,especially the vertical range of updraft,graupels and cloud water,which are almost consistent with the observations.However,the vertical wind velocity simulated is much lower than that observed.The simulation results show that the mixing ratio of rain water under the embedded convection is high,and the corresponding higher mixing ratios of ice above the embedded convection and cloud water and graupels within the embedded convection,verifying the“precipitation cores”phenomenon in the convective region.The numerical simulation sensitivity tests of orographic effect show that the increase of terrain height of Taihang mountain can increase the hydrometeor content in clouds,radar reflectivity and precipitation in its eastern area.If the height of Taihang mountain increases1.5 times,the average mixing ratio of hydrometeor increases about 20%³0%and 24-hour accumulated precipitation increases 49.5%in its eastern area,while the increase of 0.5 times in height could decrease precipitation of 20%and 6.5%respectively,indicating that the Taihang mountain plays an important role in the precipitation of its eastern region.