一次典型降水层状云的结构特征和增雨潜势分析

利用FY-2C卫星资料、雷达资料和逐时降水资料及NCAR/NCEP(1°×1°)再分析资料,对2005年9月24-25日河南省出现的层状云降水过程进行了分析。结果表明:影响降水过程的是低槽—切变云系,切变线云系为暖云云系,结构较均匀,低槽云系主体为冷云,云顶亮温不均匀,有低亮温带结构,当东移的低槽云系与北抬的切变线云系叠加后,叠加区上有中小尺度云团活动,促使降水加强。强降水出现在700 hPa、850 hPa切变线之间及500 hPa低槽前部,并与云顶亮温的发展变化趋势表现出相似性;500 hPa槽前、700 hPa切变线北侧的降水,雨强与亮温值的对应关系不确定。这主要是由于低槽云系和切变线云系的叠加部位不仅具有深厚的湿层,而且具有较强的动力抬升和水汽辐合条件;切变线北侧处于低空辐散区且水汽条件较差,自然降水产生的条件不是很好。最后借助于FY-2C卫星资料反演的云物理参数,对低槽—切变云系的增雨潜势进行了简要分析,认为低槽—切变云系上云顶温度较高的部位符合“播云窗”概念,具有很好的增雨潜势,切变线北侧的低槽云系由于云顶温度低、低空水汽不充分,“播撒—供应”机制不能很好地建立,其增雨潜势条件也弱。

Analysis on Structural Feature and Precipitation Enhancement Potentiality about Precipitation of Typical Stratiform Cloud

By using FY-2C satellite photographs,radar data,hourly precipitation data and NCAR/NCEP data,the paper analyzed the precipitation process of stratiform cloud appearing in 24~25th,November 2005 in Henan.The result shows that the trough-shear-circumfluence stratiform clouds are the main influence clouds.The shear-line clouds are warm with the uniform structure,and the trough-clouds are cold and their TBB is not uniformity with low-brightness temperature band structures.After trough-cloud system which moving eastward and shear-line cloud system which jumping northward overlaid,the movement of mesoscale clouds could be concluded and the precipitation became stronger.The strong rain appeared between the 700 hPa and 850 hPa shear lines where was in the front of 500 hPa trough-line,and the rainfall intensity had a good corresponding relationship with the brightness temperature of cloud top.The relationship between brightness temperature and rainfall intensity appearing to the north of 700hPa shear line is not sure.The main causation is that the joint of shear-line clouds and trough-line clouds not only had more abundant water vapor,but also had the better condition of dynamic lifting and convergence,especially had the condition of convective instability;and because the area in the north of shear-line is lacking in water,it is not easy for the nature precipitation to appear although there is the condition of convective instability near troposphere.At last,the precipitation enhancement potentiality is analyzed simply using FY-2C satellite retrieval data :the higher cloud top temperature part of trough-shear clouds are according with the "cloud seeding" idea,and the part in the north of shear-line has the poor precipitation enhancement potentiality because of colder cloud top temperature and lacking of water vapor and the "seeder-feeder" mechanism is not established perfectly.In conclusion,the analysis of satellite data and diagnose can be a good estimation gist for precipitation enhancement potentiality of stratiform cloud.