| Northeast China, located in the high latitude, influenced by the Asian monsoon, so the intensity and frequency of rainfall must not be less than the southern China. For there are a lot of rivers in Northeast China, some large-area heavy rainfalls could result in serious floods, endangering people's lives and property. In recent years, most scientists concentrated on the climatic analysis of summer rainfall over Northeast China, the results indicate that the 1990's are at the fluctuation period between floods and droughts and the late of 1990s were at the transition period to the drought. However, after floods in Song Huajiang Valley in 1998 and the Liaohe River floods in 2005, the study on heavy rainfall in Northeast China becomes more important.Using the 24 hours precipitation amount during 1990 to 2005, NCEP 1°×1°grid data and the TBB from FY-2 satellite, three main parts are included in this paper. The first part is the classification of heavy rainfall processes in Northeast China during 1990～2005; The second part is the analysis of structures, vorticity and moisture budgets of two different kinds of the Northeast Vortex producing heavy rainfall, which are the vortex case A (July 28, 2005)and the vortex case B(July 14～15,1998); The third part is a simulation on vortex A by using WRF (Weather Research and Forecast) model to make detailed analysis of the structure of vortex and the convective rainy cluster related to the heavy rainfall. Firstly, the general statistic characteristics of heavy rainfall processes occurring in Northeast China during 1990～2005 are analyzed and 30 cases of heavy rainfall processes are collected to be classified into six types: (1)the long distance interaction between typhoon and westerly trough or vortex(9 cases), (2)the direct interaction between landing typhoon (or vortex from southern China) and the westerly trough or vortex (7 cases), (3)the landing typhoon rainfall (1 cases), (4) rainfall ahead of the westerly trough (6 cases), (5) shear-line rainfall behind the Subtropical High (4 cases). Among them, the long distance interaction or direct interation between typhoon and systems in westerlies is the most important circulation condition for the heavy rainfall in Northeast China. Moreover, the Northeast Vortex is also one of important systems causing the heavy rainfall because there are 13 cases related to them in the total of 30 cases.Secondly, detailed analysis are made on the structure, vorticity and moisture budgets of two different kinds of the Northeast Vortex cases A and B mentioned -above.The results show: (1) In the early development stage, the occurrence of closed center of Northeast Vortex in the middle level is earlier both than the lower and upper levels. The vortex A develops deeply with the appearance of closed center at 200 hPa, but the vortex B just is in middle and the lower level without closed center at upper level. (2) Northeast Vortex is not entirely similar to the traditional Northeast Cold Vortex, for the vortex A is obvious cold structure with 700 hPa～200 hPa while the vortex B is not. (3) The high-latitude blocking high plays important role in the maintenance and development of Northeast Vortex. (4) the maximum of potential vorticity anomaly, located in the upper troposphere, extends downwards to the east part of Northeast Vortex, which is near to the area of heavy rainfall. The interaction between downward potential vorticity and the baroclinicity front in lower level is beneficial to the development of Northeast Vortex. (5) The calculation of vorticity budgets indicates that both horizontal advection term and horizontal divergence term contributed most importantly to the strengthening of vortex. The distribution of horizontal advection term term, which is positive in upper and negative in lower troposphere and the vertical advection, play indirect role in the development of ground cyclone.(6) The rainy area and the intensity of heavy rainfall in Northeast China are closely related to the coupling of low level and upper level Jet.Thirdly, Numerical simulation of vortex A for 48 hours shows that WRF model is capable for simulating the weather pattern of Northeast Vortex, only the strength of vortex in middle and upper level is slightly weaker.The rainfall simulation is consistent with the observations, but slightly weaker in the precipitation amount. During the development of vortex, positive vorticity exists in the whole troposphere and the maximum of positive vorticity was extended from the upper level to the lower level, which is the same as the analysis results. The heavy rainfall of vortex occurred mainly in the early night because at this time the pseudo-potential temperature below 700 hPa decreases with height, leading to the potential instability which is conductive to the occurrence of convective. The simulation results also show in detailed that the influence of upper level potential vorticity abnomoly and the interaction between upper and lower levels. The simulation of 310 K–entropy analysis reveals the cold and warm air flow characteristics in the middle and lower levels and verifies the intrusion of northeast dry and cold air is beneficial to the maintaining and develping of Northeast Vortex. The rainfall of vortex is mainly caused by the spiral cloud bands and the maximum precipitation is related to the convective rain cluster in the northeasten part of vortex. The rainfall cluster locates at area of the maximum gradient of TBB. The southerly wind turns to be southeast and produces shear convergence with the easterly wind in the north of vortex, which is favorable to the development and maintenance of the vortex. In addition, WRF model can successfully simulate the cold core structure of vortex, but the simulation of relative humidity and upper level jet at 200 hPa is weaker which may be the causes for smaller WRF simulated rainfall.Finally, more studies on the local heavy rainfall with high intensity should be conducted in the future and the mechanism of Northeast vortex development is also needed to be further studied.
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