"05.6"东北暴雨中尺度对流系统研究Ⅰ:常规资料和卫星资料分析

应用常规气象资料与卫星资料相结合的办法,研究了2005年6月10日午后在黑龙江省中东部发生的暴雨中尺度对流系统(MCSs)的大尺度环流背景、大气层结演变特征、下垫面条件以及中尺度对流系统。结果表明:此次暴雨(简称“05.6”东北暴雨)是发生在高空槽东移加深过程中的一次对流天气过程。中尺度对流系统处于前倾疏散的高空槽槽前,高空辐散,低空辐合,为MCS发生提供了有利的大尺度动力条件。暴雨发生前对流层低层有西南—东北走向的湿舌,为暴雨提供了有利的水汽条件。高空干冷平流与低空的暖湿平流形成的差动平流,造成此处大气的层结不稳定度增强。此外,从地面接收到的太阳辐射能量分布情况来看,下垫面不均匀加热引起的热力环流是这次暴雨过程中尺度对流系统发生发展的一个重要的触发机制。研究地面中尺度切变线演变与此次暴雨对流系统发生发展的关系发现,切变线上对流强弱分布是不均匀的,其中在弧形切变线曲率最大处的对流最强,与沙兰河上游暴雨有关的对流云团就出现在这个地区。以上事实表明,地面中尺度切变线可能是此次暴雨发生发展的另一个关键因素,而造成切变线上对流发展不均匀的原因可能和切变线走向与环境风场的配置有较大关系。

THE RAINSTORM AND MESOSCALE CONVECTIVE SYSTEMS OVER NORTHEAST CHINA IN JUNE 2005 Ⅰ: A SYNTHETIC ANALYSIS OF MCS BY CONVENTIONAL OBSERVATIONS AND SATELLITE DATA

Large-scale environmental condition and meso-scale convective systems(MCS)related to the heavy rainfall responsible for the severe mud-rock flow disaster in the eastern central portion of Heilongjiang province on 10 June 2005 are studied with the conventional observations and satellite data.An elementary diagnosis is performed to the large scale circulation,the stratification evolution,the underlying surface condition and the MCSs.The findings from the analysis are as follows:This rainstorm is a classic mesoscale convective weather event that occurred in the eastward-moving and deepening process of an upper-level trough with a forward-tilting and diverging structure.The MCSs producing the rainstorm,were in the front area of the upper trough,where the upper level divergence-lower level convergence provided a favorable large-scale dynamic background for MCSs' development.Viewed from the stratification characteristics of temperature and humidity,a SW-NE stretched lower level warm and moist tongue was obviously seen before the occurrence of the rainstorm,and the tongue fed the rainfall area with plentiful and sufficient moisture.The differential advection induced by the dry/cold advection at the upper level superposing on the warm/moist advection at the low level strengthened the local instability of atmospheric stratification within the rainstorm area.Furthermore,the horizontal distribution of the incident solar radiance at the underlying surface shows that the thermodynamic vertical circulation induced by the differential heating may be one of the most important trigger for the spawn and development of MCSs.With respect to the relationship between the evolution of surface meso-scale shear line and the genesis and development of MCSs in the rainstorm process,it is found that the strength of the convective cells along the shear line was not equal,with the most vigorous convective cells located around the maximum curvature point of the shear line,and according to the satellite cloud images and the observational surface data,the cloud clusters directly responsible for the rainstorm just lay in the vicinity of the maximum curvature point of the shear line.These facts seem to indicate that the surface meso-scale shear line may be another key factor for the rainstorm and the convection non-homogeneity on the surface meso-scale shear line may be partly related with the disposition of the shear line and the ambient winds.