Abstract: Two northward motion tropical cyclones affecting Tianjin,called Haima (0421) and Damrey (1210),were analyzed using FY-2E TBB (Temperature of Black Body),GMS (Geostationary Meteorological Satellite) TBB and NCEP (National Centers for Environmental Prediction) 1°×1° reanalysis data.The results show that the rainfall triggered by the two tropical cyclones exhibits asymmetric distributions and occurs in the northern and northwestern sides of Haima and northeastern side of Damrey,in connection with the asymmetric distributions of dynamic and thermodynamic conditions.The two tropical cyclones interact with westerly trough to some extents when moving northward.The difference is that Haima interacts with a deep trough and couples with southward jet stream in front of the trough.A higher potential vorticity on the upper troposphere transports downward to lower troposphere to facilitate the development of a surface cyclone.Whereas Damrey strikes a weak trough,only appearing near the bottom of the trough,and the coupling effect is not significant.There is no a clear positive potential vorticity transporting downward to lower levels of the troposphere,so it is not favorable for the development of a surface cyclone.Therefore Haima weakens first and then intensifies again after landing,but Damrey weakens continuously till disappears in the Bohai Sea.

Key words: Northward tropical cyclone, Asymmetric distribution, Upper trough, Potential vorticity