| ENSO is the most important external forcing signal for seasonal prediction of the East Asian atmospheric circulation.In recent decades,different warming patterns of tropical Pacific sea surface temperature(SST)and their climate impacts have become popular studies.In this thesis,we discuss the characteristics of East Asian climate anomaly during various El Ni(?)o events from different aspects using the reanalysis data of Had ISST,NCEP,ERA5,and SODA,focusing on the connection between the warm SST anomaly zonal location of CP El Ni(?)o and East Asian climate.And the corresponding mechanisms are discussed in this work.The main findings of the study are as follows.The reason for the significantly weaker effect of CP El Ni(?)o on the SST over cold tongue(CT)region in the South China Sea(SCS)compared with EP El Ni(?)o is related to the warm sea surface temperature anomaly(SSTA)zonal location of CP El Ni(?)o.When the location is relatively eastward(named ECP El Ni(?)o),the CT region is accompanied by positive SSTA,which exhibits a similar and comparable evolution with that of EP El Ni(?)o events.On the contrary,when the location is relatively westward(named WCP El Ni(?)o),the CT region is accompanied by negative SST anomaly.Therefore,the weak and insignificant SST anomaly over the CT region during CP El Ni(?)o events is caused by the faint SSTA response during the WCP El Ni(?)o events.El Ni(?)o modulates the SCS climate mainly through the excitation of anomalous western North Pacific anticyclone.And the warm SST anomaly zonal location of CP El Ni(?)o influences the position and intensity of this anomalous anticyclone,which in turn affects the SST over the CT region in the SCS through sea-air interactions.In addition,the anomalous SST presents a double-peak warming evolution over the CT region during El Ni(?)o events in winter and summer,respectively.The formation of the winter-spring warming results from joint atmospheric and oceanic forcing,while the summer warming is mainly caused by oceanic forcing,with atmospheric processes even playing a negative role.The warm SSTA zonal location of CP El Ni(?)o also affects the East Asian summer monsoon.The precipitation during the main flood period is significantly above-normal in all regions during ECP El Ni(?)o events,and the evolution characteristics of SSTA are similar to those of EP El Ni(?)o.However,the impact of the ECP El Ni(?)o events on precipitation in South China is more stable and significant than that of EP El Ni(?)o.On the contrary,the precipitation is abnormally low during the main flood period in each region during the WCP El Ni(?)o events.The influence of ECP El Ni(?)o and WCP El Ni(?)o on the seasonal process of East Asian summer monsoon is mainly observed during the Spring Persistent Rains in Jiangnan,the period of plum rain in Jianghuai region,and the East Asian summer monsoon advancing northward from mid-late May to early July.The warm SSTA zonal location of CP El Ni(?)o also affects the intensity and position of the northwest Pacific anticyclone,which in turn affects the East Asian summer monsoon process.During the ECP El Ni(?)o events,the anomalous western North Pacific anticyclone at 850 h Pa and the western Pacific subtropical high at 500 h Pa is located southward and with stronger intensity,which is not conducive to the northward advance of the summer monsoon,resulting in a long duration of the main flood period in each region.On the contrary,the northwest Pacific anticyclone at 850 h Pa and the western Pacific subtropical high at 500 h Pa is located northward in the WCP El Ni(?)o event.Therefore,the East Asian summer winds are advancing northward at a fast rate,resulting in a shorter duration of the main flooding period.In the context of global warming,the relationship between ENSO and East Asian climate has become increasingly unstable.Some studies have even suggested that ENSO cannot be the main basis for seasonal prediction of East Asian climate.And this study emphasizes that the increasingly unstable relationship between them is mainly attributed to the diversity of El Ni(?)o,especially the complexity of CP El Ni(?)o.Therefore,in addition to the intensity of CP El Ni(?)o,we also need to pay attention to the warm SSTA zonal location of CP El Ni(?)o and its influence on the East Asian climate,which will provide important information for the seasonal climate prediction in East Asia. |
