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In early summer 2020, eastern China was hit by record-breaking Meiyu rainfall. The anomalous western Pacific subtropical high (WPSH) played a crucial role in this event. This paper exposes the abnormal features of the WPSH and its related vertical circulations and reveals its dynamical causes in this period, from the perspective of the three-pattern decomposition of global atmospheric circulation (3P-DGAC). Analyzing the anomalous spatial patterns of the three stream functions R, H, and W of the horizontal, meridional, and zonal circulations defined by the 3P-DGAC, we discovered that the WPSH described by R at 850 hPa was intensified and westward from the horizontal circulation. For the vertical circulations, the local meridional circulation along East Asia expressed by H manifested an abnormal downdraft at 20° N, which was beneficial to strengthening the WPSH. The zonal circulation in the tropical Pacific represented by W was anomalously far to the west, which was related to the westward extension of the WPSH. Then, to uncover the causes of the anomalous WPSH from the dynamics, we used the vorticity equation based on the 3P-DGAC and found that the negative relative vorticity advection anomaly over the western Pacific played a key role in this event. Due to the positive sea surface temperature (SST) anomaly and enhanced convection over the Maritime Continent (MC), local vertical circulations at low latitudes were significantly activated. The intense local meridional circulation along East Asia carried the relative vorticity from the MC to the western Pacific and strengthened the WPSH. The ascending branch of the zonal circulation in the tropical Pacific moved westward, which may favor the westward extension of the WPSH. This study represents a promising step in revealing the three-dimensional (3D) structure and internal dynamics of anomalous WPSH. [ABSTRACT FROM AUTHOR]

Based on monthly rainfall station data from the National Climate Prediction Center of China Meteorological Administration, reanalysis monthly data from NCEP/NCAR including the monthly mean and long-term mean values for geopotential height, winds of multi-levels, NOAA(National Oceanic and Atmospheric Administration) monthly Sea Surface Temperature (ERSSTV5), the causes of anomalous excessive precipitation in 2021/2022 winter over South China (SC) are investigated by Liang-Kleeman information flow, composite and wave flux methods. The results show that the winter precipitation over SC in 2021/2022 DJF is far more than normal, and the associated circulation patterns are obviously different from those induced by traditional La Niña, especially in the Atlantic and East Asia areas south to Lake Baikal. In 2021/2022 DJF, the Tibet Plateau (TP) exists anomalous cyclone with strong ascending motion, which directly affects the circulation patterns in Eastern China and thus the precipitation in SC. It is a significant causal relationship for the earlier season velocity potential at 850 hPa (related to the anomalous SST) over the tropical Atlantic to later DJF anomalous vertical motions over TP. Especially when the anomalies in tropical Atlantic leads one month before, the relationship is closest. The anomalies of the tropical Atlantic can stimulate the Rossby wave train which propagates downstream, corresponding to the abnormal cyclonic circulation over TP. In the early autumn to winter of 2021/2022, the 850 hPa potential velocity anomalies in the tropical Atlantic were significant with positive phase. The Rossby wave train excited by the potential velocity anomalies and then propagated along the great circle path and global jet stream (GJT) over South Asia (SA), formed an anomalous cyclonic with ascending motion over TP and lead more precipitation over SC in winter of 2021/2022. Winter rainfall, usually accompanying with lower temperature, will bring severely bad influence on traffic, power supply, communication, agriculture and people's lives. The results of this paper can provide a reference for further understanding the causes and mechanism of DJF rainfall over SC. • The winter precipitation over SC in 2021/2022 DJF is extremely more than normal, and the associated circulation patterns are obviously different from those induced by La Niña, especially in the Atlantic and East Asia areas south to Lake Baikal. • Strong ascending motion over TP(Tibet Plateau) affects the circulation patterns directly in eastern China and lead to the excessive precipitation in SC during 2021/2022 DJF. • The anomalies over the tropical Atlantic can stimulate the Rossby wave train and propagate downstream, and the Rossby wave trains allow energy to propagate to TP area with wave flux convergent, contributing certainly to the anomaly cyclone circulation there. [ABSTRACT FROM AUTHOR]