Based on multi-year reanalysis data, Prof. XUE Feng from Institute of Atmospheric Physics and his student ZHAO Jun-Jie studied the intraseasonal variation of the EASM and summer rainfall over East Asia in La Niña years (Xue and Zhao, 2017). They find that owing to a higher SST over the western Pacific warm pool in the preceding winter and spring, warm pool convection in summer is enhanced. As a result, the WPSH extends more northeastward. This anomalous pattern tends to change with the march of the seasons, with a maximum anomaly in July (Figure 1). The rainfall distribution in East Asia in La Niña summers is characterized by a zonal pattern of less rainfall over eastern China and more rainfall over the oceanic region of the western Pacific. By comparison, a meridional pattern is found in El Niño summers, with less rainfall over the tropics and more rainfall over the subtropics and midlatitudes. 

Figure 1. Rainfall anomaly in La Niña years (units: mm d⁻¹) and the 500 hPa western Pacific subtropical high (units: gpm). Regions with statistically significant results at the greater than 95% confidence level are shaded. The black and red contours represent the WPSH in La Niña years and the climatological mean, respectively. (Xue and Zhao, 2017)