Summer onset in northern Asia.

In this study, the northern Asian summer onset (NASO) is investigated in terms of its key features, thermodynamic driving factors, and its associations with the rainfall pattern in eastern China on the basis of the U.S. National Centers for Environmental Prediction and the U.S. National Center for Atmospheric Research reanalysis data, the snow cover extent data archived by the National Oceanic and Atmospheric Administration's National Centers for Environmental Information, and the precipitation data of observational stations in China. We define the NASO as the critical time when seasonal surface warming in northern Asia accelerates prior to this time and then stabilizes after this time. The climatological NASO occurs in the second pentad of June, across which systematic changes occur in the near surface warming in northern Asia. The heat budget analysis demonstrates from the climatic perspective that the snowmelt process in northern Asia plays a crucial role in the NASO. The positive feedback between surface warming and snowmelt facilitates an intense surface warming associated with the NASO. It is revealed that large‐scale wave patterns in the sea‐level pressure field contribute to early and late advents of NASOs. In association with the wave patterns, the horizontal linear advection term and adiabatic term are the primary thermodynamic drivers to the early and late NASOs. From late May to early July, the circulation anomalies from northern Asia to the subtropical western Pacific are significantly different between the early and late NASO years. Accordingly, in the rainy period, the seasonal evolution of rainfall pattern in eastern China also shows a considerable difference in these two NASO years. [ABSTRACT FROM AUTHOR]