The influence of east-west displacement of Northwestern Pacific subtropical high on east-west difference of precipitation in southern China in early summer

The Northwest Pacific Subtropical High (hereinafter referred to as the subtropical high, NWPSH) is a large-scale circulation system affecting China climate. To further understand the impact of the NWPSH east-west movement on the China climate, based on the precipitation data of observational stations and re-analysis of atmospheric circulation data, the influence of this movement on precipitation in June in south China, as well as the ocean factors affecting the NWPSH are investigated by using diagnosis analysis and numerical simulation. The results show that the influence of the NWPSH east-west movement on precipitation in southwest China and South China is obviously different : the NWPSH westward movement is favorable for the precipitation to be more in Southwest China and less in South China, while westward movement is just the opposite. The reason for such a difference is related to the circulation variation caused by the NWPSH east-west movement. The northeast (southwest) wind anomaly in the northwest side of the NWPSH and the anomalous meridional wave train at the middle and low latitudes in East Asia are directly related to the precipitation variation in South China. However, the precipitation anomaly in southwest China is close related not only to the zonal wind anomaly caused by the NWPSH east-west movement in southeast Asia, but also to the influence of the dynamic action of the Tibetan Plateau on the zonal wind of the north side of the NWPSH. Otherwise, the source of water vapor in the southwest and south China is different when the NWPSH moves eastward or westward, and the water vapor in the southwest China comes mainly from the cross-equatorial flow near 80 degrees E in the Indian Ocean, while the water vapor in the South China comes from the easterly flow of the south side of the NWPSH from the Northwest Pacific. The dipole-like Sea Surface Temperature Anomalies (SSAT ) in the tropical northwest Pacific and in equatorial western Pacific in the early winter and spring is closely related to the NWPSH east-west displacement in sequent early summer. The warm SSTA in northwest Pacific and cold SSTA in the equatorial western Pacific are beneficial to the subsequent NWPSH movement westward and vice versa. The numerical simulation further proves the influence of dipole-like SSTA on the NWPSH east-west movement.