The air-moisture ratio is one of the products of the Chinese FY-3A satellite.The product enables atmospheric moisture conditions to be described at fine scale.By overlapping the air-moisture ratio field of FY-3A and the wind streamline field at low level together,the quantitative diagnostic and pre-estimate on precipitation over local area can be done.Due to the fact that the satellite data and reanalysis data come from different digital sources,and have their own coordinate systems,it is needed to build the same coordinate as a base for both datasets.The satellite coordinate changes with time as its covering area is different to any given position on Earth,so it needs to transfer the satellite coordinate into the coordinate of the wind streamline fields.The whole data preprocessing includes the following steps:interpolation of the vertical standard pressure levels from the satellite's own pressure levels;switching the satellite orbit coordinate into the traditional latitude-longitude coordinate;deleting outliers via the Bi-weight Check method,smoothing the data field and removing the data "noise" by the nine smooth method;Testing preprocessing results via cross-correlation testing,to check that the fine-scale features of satellite data are still keep satisfactory.For analysis of the wind streamline fields,key systems of heavy rainfall need to be determined at first.According to 5 year (2009-2013)statistics,the shallow low vortex and convergence line are two key system types for heavy rainfall over the Jianghui Valley during the Meiyu season.Three of five low vortices are active in the downstream area of Changjiang River,and two of three convergence lines are active in the Huaihe Basin.Synthetic analysis of these typical systems according to their different types shows that the convergence line is associated with a moisture front that has a stronger latitude directional,whereas the low vortex is associated with a longitudinally directed wet tongue and more blending of the wet and dry air masses.Furthermore,by carrying out the combinational analysis of the FY-3A air-moisture ratio distribution and wind streamline field of heavy rainfall at the same moment,the results show that the large-value areas of FY-3A air-moisture ratio corresponding to the cyclonic convergence areas in the streamline fields.The area can indicate the locations of heavy rainfall at fine scale.The atmospheric precipitable water amount at low levels (1000-850 hPa)can be calculated according to the FY-3A satellite air-moisture ratio,The precipitable water amount and the high energy area of the pseudo-equivalent potential temperature,especially the high-energy fronts in the rainfall area are all proportional to the precipitation intensity.To apply the satellite moisture-dynamic diagnostic method over a near-shore area,the precipitation location and intensity at the sea area can be estimated,which compensates efficiently for the shortage of observations at sea.