Abstract:

Using daily precipitation data from 54 meteorological stations and daily reanalysis data from the NCEP/NCAR (National Center for Atmospheric Research and National Centers for Environmental Prediction in the United States) in Liaoning province from 1971 to 2020, the Standardized Precipitation Index (SPI) for the water demand key period of soybeans (from flowering to pod-setting phase) was calculated for each station in Liaoning province. The typical drought years and the atmospheric circulation causes during the water demand key period of soybeans were analyzed. The results show that the different configuration of tropospheric circulation in high and low levels caused by the anomaly of subtropical westerly jet is the main cause of the atmospheric circulation in the dry years with different climatic characteristics during the key period of soybean in Liaoning province.When the position of westerly jet in the water demand key period of soybean is more northerly than usual, it is prone to high temperature and drought, and the main soybean producing areas in Liaoning province are affected greatly. The westerly jet is located to the north, and Liaoning province is located to the south of the upper jet axis and the center of the upper divergent wind field. The West Pacific subtropical high is anomalously northward in phase, which controls the whole Liaoning province. The main cause of high temperature and drought is the poor water vapor condition of the downdraft through the tropospheric wind field.Low temperature and drought are easy to occur when the westerly jet is located in the south during the water demand key period of soybean, and the central and northern parts of the main soybean producing areas in Liaoning province are more affected. The position of the westerly jet is southward, and the seasonal process is slow. The position of the Western Pacific subtropical high continues to be southward and west compared with the usual year. The vertical upward movement of the upper troposphere is obvious, and the cold air activity is frequent.However, the consistent subsidence movement in the middle and lower troposphere combined with poor water vapor conditions is not conducive to precipitation, resulting in the simultaneous occurrence of low temperature and drought.

Key words: Water demand key period of soybean, Drought, Westerly jet stream, Subtropical high over the western Pacific