Analysis of atmospheric circulation characteristics of regional rainstorm reinforcement associated with typhoons making landfall in northern Fujian and southern Zhejiang

Using the historical records of typhoon landing in northern Fujian and southern Zhejiang during 1950-2015, the typhoon path is divided into groups moving westward and northward after landing. The atmospheric circulation and physical parameter features, separating whether there is a regional typhoon rainstorm reinforcement or non-occurrence in Zhejiang, are extracted under the two different types path typhoon influence, and the distribution of rainstorm reinforcement is also discussed. The results show that it has clear difference between rainstorm reinforcement occurrence and non-occurrence in the westward and northward track typhoons. When regional typhoon rainstorm reinforcement occurred in Zhejiang, before and after the landfall of typhoon, the water vapor channel and E-SE jet in the mid-low troposphere have extended from the South China Sea, east of Taiwan to the coast of Zhejiang and into Zhejiang inland. There is a high-level divergence and low-level convergence structure near typhoon center, and with an east warm and west cold pseudo-equivalent temperature advection field structure. If there is weak cold air intrusion, rainstorm reinforcement intensity is stronger and larger, and rainstorm reinforcement falling area is stretched to the north of Zhejiang. The non-reinforcement rainstorm typhoon has no obvious southerly jet in the South China Sea to Taiwan or SE jet axis, and the low-level water vapor channel over coastal Zhejiang is to the north and east, not into Zhejiang inland, and the strength is weaker. Zhejiang is in the SE side of the continental warm air mass, and there is no obvious warm advection in the Zhejiang coast, also no high-level divergence nor weak high-level divergence and low level weak convergence near typhoon center.