A Review of Physical Mechanisms of the Global SSTA Impact on EASM

The impact of global sea surface temperature anomaly (SSTA) on the East Asia Summer Monsoon (EASM) and summer precipitation in China is reviewed from the aspects of physical mechanisms, on the basis of key external forcing signals in short-term climate prediction. Focusing on El Niño-Southern Oscillation (ENSO) cycle in the tropical Pacific and the main SSTA modes in Indian and Atlantic Ocean, their inter-annual variability are further reviewed as well as their different impacts on the EASM, especially their relationship with the main summer rainfall belt in China.During different phases of ENSO cycle, ENSO exerts different impacts on the EASM and the summer precipitation in China. In the developing summer of El Niño, the EASM tends to be weak and the main summer rainfall belt would shift southward in eastern China. However, in the decaying summer of El Niño, the EASM tends to be strong, and the summer precipitation would be below normal in the Yangtze-Huaihe Valley. The situations are approximately reverse for the impact of La Ni a on the EASM and summer precipitation in China, although the impact of La Ni a is not as significant. The influence of ENSO on the EASM and the summer rainfall belt in China is closely correlated with the SSTA in the western Pacific warm pool as well as the resulted convective activities in its northern part. Moreover, the Philippine Sea anticyclone also plays an important role. In recent years, different types of El Niño are widely discussed. It is revealed that the Central Pacific (CP) El Niño not only has different evolution mechanisms, but also shows different impacts on the global atmospheric circulation as compared with the Eastern Pacific (EP) El Niño or classical El Niño.Indian Ocean SSTA modes also show significant influences on the EASM and the summer precipitation in China. For example, the basin-wide warming (cooling) mode in the tropical Indian Ocean would cause a late (an early) South China Sea summer monsoon (SCSSM) onset; in the summer of positive (negative) tropical Indian Ocean dipole phase, more precipitation would occur in South China (North China); during the positive (negative) phase of subtropical southern Indian Ocean dipole, Indian summer monsoon tends to be stronger (weaker), and SCSSM may establish earlier (later). The positive (negative) North Atlantic tri-pole mode would lead to a stronger (weaker) EASM through motivating quasi-barotropic zonal tele-connection wave train across the Eurasian continent.SSTA is the important pre-signal on the prediction of summer precipitation anomaly in China. Because of the predictability of short-term climate prediction, it is still difficult to give high skill prediction for summer rainfall anomaly in China. Some advices and requirements on the physical mechanism research and dynamical model development are proposed in order to improve the prediction of the EASM and summer rainfall in China.