The relationship between summer tropical Atlantic sea surface temperature and the first rainy season precipitation in South China without ENSO impact

This study emphasizes the impact of the summer tropical Atlantic (TA) sea surface temperature anomalies on the precipitation of the first rainy season (April to June) of the following year in South China without the influence of the El Niño/Southern Oscillation (ENSO) during 1979 to 2019.There is a significant negative correlation between precipitation during the FRS in South China and preceding summer TA SST anomalies. Higher (lower) TA SST in the preceding summer tends to correspond to reduced (increased) precipitation during the subsequent FRS in South China. During years with TA SST anomalies, anomalous diabatic heating in the boundary layer excites a Gill-type Rossby wave response in the lower troposphere north of the equatorial Atlantic. By the subsequent FRS, the Rossby wave response propagates further northward and westward, inducing a geopotential height anomaly pattern over the North Atlantic resembling the North Atlantic Oscillation (NAO). This promotes the formation of a tripole-like SST anomaly pattern in the North Atlantic during the FRS, which in turn excites downstream-propagating Rossby wave trains, influencing the atmospheric circulation over Eurasia. When the TA SST exhibits negative (positive) anomalies in summer, the Rossby wave trains over Eurasia during the subsequent FRS significantly strengthen (weaken) the Ural Mountain ridge and the cyclonic circulation around Lake Baikal. On the one hand, this accelerates (decelerates) the upper-level zonal winds over southern China, promoting the intensification and southward expansion (weakening and northward retreat) of the subtropical westerly jet. This favors anomalous upper-level divergence (convergence) over South China, leading to anomalous ascending (descending) motion and increased (decreased) precipitation. On the other hand, it enhances (weakens) the prevalence of anomalous northerly (southerly) winds over Siberia, making it easier (harder) for mid-high latitude cold air to intrude southward. This strengthens (weakens) low-level frontogenetic forcing over South China, favoring (inhibiting) the development of ascending motion and thereby enhancing (reducing) precipitation.