1.National Climate Center,Beijing;2.Tianjin Climate Center,Tianjin
Meiyu precipitation has significant stage changes. It is important to study the key circulation stable components that lead to continuous heavy rainfall for the analysis and prediction of Meiyu precipitation. Using NCEP/DOE Reanalysis II data from 1979 to 2016, the potential height field, wind field and relative humidity field during the Meiyu period in 2016 were analyzed, the key stable components of the circulation system were extracted, the spatial structure, evolution characteristics and the background situation of longer time scale were analyzed, which provided the basis for the extended period forecast of the periodic heavy rainfall in Meiyu area Reference resources. The results suggest that: (1) The distribution of "three poles" in the stable components of the geopotential height field is the key system to maintain the continuous heavy rainfall in Meiyu area in 2016. The "three poles" correspond to the Ural Mountains blocking high, the Okhotsk Sea blocking high, the Southeast Asia high and the West subtropical high. This configuration structure is conducive to the convergence of warm and cold air in Meiyu area to form persistent heavy rainfall. (2) In the middle and high latitudes, there is a relatively deep negative anomaly between the two deep positive anomaly areas. On the one hand, it is conducive to the South transportation of cold air. On the other hand, the stable component of relative humidity field indicates that the water vapor transportation and convergence of the northern branch of the air flow play an important role in the continuous precipitation of Meiyu area. (3) The positive anomaly area in the middle and low latitudes is zonal in the east-west direction, and mainly exists in the middle and high troposphere, but there is a positive area on the East-West side of the Meiyu area, which continues down to the lower level, and they together strengthen the convergence and transportation of warm and humid air flow in the south of the Meiyu area. (4) Through the analysis of the evolution of the stable component, it is shown that the establishment and evolution of the "three pole" system lead to the precipitation in Meiyu area showing different stage characteristics.(5) The longer time scale (60 days) circulation stable components provides an important circulation background for the key stable components of the "three pole" in the period of continuous heavy rainfall.