Abstract: In this paper,the data from the conventional meteorological stations,the intensively meteorological automatic observation stations,and the NCEP (National Centers for Environmental Prediction) reanalysis were used to comparatively diagnose and analyze the typhoon and rainstorm processes,Haitang (1710) and Damrey (1210),which occurred in Dalian on August 3,2017 and 2012,respectively.Through analyzing the typhoon track,circulation situation,and interaction between the two typhoon systems,it is shown that the precipitation system during the two rainstorm processes is a typical double-typhoon precipitation mode.In the north of the typhoon systems,there are cold air with different intensities invading and triggering convective instability,which facilitates the development of mesoscale rainstorm cloud clusters.There is a shear convergence at the lower 850 hPa,and a jet stream developing at the upper level.During the main rainfall periods, a strong upward movement from the low to the high levels occurs over the heavy precipitation center,and the divergence at a high level and convergence at low level are maintained over the rainstorm center.The typhoon system existing at the south of Japan sea forces the subtropical high to develop a radial distribution or to form a blocking high.The jet at low level formed between the two or three typhoons and the subtropical high provide favorable dynamic and water vapor conditions for the formation and maintenance of the rainstorms.Combined with the residual circulation of typhoon "Haitang" and the high trough,the cold air brought by the high trough is more intense and the effect of frontogenesis is more obvious,which is favorable to the occurrence and development of strong convection.The interaction between typhoons "Sula" and "Damrey" affecting Dalian leads to more vigorous warm and wet airflow,longer duration and a wider range of precipitation during the heavy precipitation stage.

Key words: Typhoon, Upper trough, Frontgenesis, Water vapor transportation