1.Chongqing Climate Center;2.International Center for Climate and Environment Sciences,Institute of Atmospheric Physics,Chinese Academy of Sciences;3.Key Laboratory of Meteorological Disaster,Ministry of Education,Nanjing University of Information Science Technology
In this paper, the anomalous characteristics of precipitation in the east of southwestern China (ESWC) in June-July,2020 and the related large-scale characteristics of water vapor transport, water vapor budget and water vapor source are analyzed by using correlation, regression, clustering, Lagrange trajectory model HYSPLITv5.0 simulation and other statistical methods based on the daily precipitation data of 118 stations and other reanalysis data. Then some indexes of water vapor intensity in key areas are defined, and the relationship between water vapor intensity in key areas and sea temperature and snow cover in Qinghai-Tibet Plateau in early winter is investigated. The results show that the average precipitation in the ESWC in June-July, 2020 is 50% more than that in normal year, which is the highest since 1961. Precipitation in most areas is obviously higher than that in normal year, except for some areas in central Guizhou and northeastern Sichuan. The configuration of tropospheric atmospheric circulation field in June-July, 2020 is a typical rainy circulation situation in the ESWC. at 200hPa, the position of the upper jet stream leans to the south, resulting in frequent and southern cold air activity. At the same time, the ESWC is located just south of the jet axis, with strong divergence outflow from the upper layer and strong convergence inflow from the lower layer, which provides favorable dynamic conditions for precipitation. In addition, the Western Pacific Subtropical High (WPSH) obviously extends westward, and the warm and humid airflow in the southwest side of the WPSH is transported to the ESWC, which is conductive to more precipitation in this region. The qualitative water vapor source calculated by Euler method and the quantitative water vapor trajectory tracking results calculated by Lagrange method both show that: the water vapor associated with precipitation in the ESWC in June-July, 2020 mainly comes from the warm and humid airflow in the southern ocean, such as Bay of Bengal, South China Sea and Arabian Sea, while the dry and cold air in the north also transports water vapor to this region, but the water vapor content is much smaller than that in the southern ocean. In the previous winter, the snow cover area of the Qinghai Tibet Plateau was relatively large, and the SST of the Indian Ocean and the equatorial Middle East Pacific was relatively high, resulting in the weakening of the west wind in the bay of Bengal, the strengthening of the east wind in the South China Sea, and the strengthening of the south wind in the northern part of the Indochina Peninsula. This feature is just the typical wind field feature of the strong and westward WPSH, which is beneficial to strengthening of the westward water vapor transport in the Bay of Bengal and the South China Sea, and the strengthening of northward water vapor transport in the Indochina Peninsula. This makes the water vapor in the southwest side of WPSH continuously be transported into the ESWC, resulting in more precipitation in this region.