The Analysis For The Change Of Precipitation During Strong El Ni(?)o Events Under High Emission Scenarios

The concentration of CO₂ has been rising since the industrialization began,the increased CO₂ would not only induce the global warming but influence the atmospheric circulation and lead to a series of anomalous climatic phenomena.El Ni(?)o-Southern Oscillation(ENSO)is the most remarkable signal of air-sea interaction,which has crucial impact on the global climate change through teleconnections.The higher emission can affect the features of strong eastern Pacific El Ni(?)o(EP-El Ni(?)o),and leads to the climate anomaly,including the change of precipitation anomaly.Based on the Coupled Model Intercomparison Project Phase 5 and 6,and a set of General Circulation Model(GCM)simulations from Cloud Feedback Model Intercomparison Project(CFMIP),the changes of the characteristics of strong EP-El Ni(?)o events and the precipitation anomaly over East Asia during strong EP events under different emission scenarios are analyzed.The changes of global precipitation anomaly in response to high emission scenario and the precipitation anomaly under different CO₂levels over East Asia are also analyzed.This study mainly focuses on the mechanisms connected with the changes of precipitation anomaly over East Asia.And finally,we discussed the possible linkage between the precipitation anomaly and the precipitation change for the climate state,and also analyzed the contribution of strong EP-El Ni(?)o events on the skewness of precipitation anomaly.The conclusions are as follows:1.It can be found that the models from CMIP5 and CMIP6 can generally well simulate the characteristics for EP-El Ni(?)o events and the global precipitation anomaly during strong EP events.Surprisingly,there seems to be no improvement in CMIP6 for the performances in simulating the precipitation anomaly over East Asia,especially in the following summer.We can see that the frequency and variability for the strong EP events increase with the higher emission scenario.2.During strong EP-El Ni(?)o events in response to the high emission scenario compared with historical experiment,the variabilities for the precipitation anomaly could increase owning to the increased standard deviations for most global areas.We can see that it agrees with the'The wet get wetter and the dry drier'mechanism over most parts of global regions in response to high CO₂ level,except for the East Asia and the parts of west of North America.For East Asia,the precipitation anomaly intensifies over the north of Yangtze River Valley in winter and the south of China in the following summer as emission increases.For the monthly changes of precipitation anomaly under high emission scenario during strong EP-El Ni(?)o events,it shows the positive anomaly over the north of the Yangtze River Valley and the negative value over the south of China from December to the following March,and the distribution reverses during May to August in the following year.3.In response to RCP8.5 experiment for strong EP-El Ni(?)o events during winter time,an intensified anticyclone anomaly exists over the south of China,which reflects the weakened EAWM,while it shows the cyclonic circulation over the north of the Yangtze River Valley.The convection weakens over the tropical Pacific Ocean area and expands northward to the south of China,probably induced by the decreased SSTA over the western Pacific Ocean during strong EP events,which is unfavorable for the formation of rainfall over the south of East Asia.As for the moisture budget anomaly,the terms influenced by the changes of circulation anomaly in response to the high emission scenario during strong EP-El Ni(?)o events have the most important contribution to the moisture transportation anomaly.The influences connected with the Combination mode(C-mode)are also estimated,and the results show that the strong El Ni(?)o itself leads to the positive precipitation anomaly and the generally same distribution of southwesterly in space over the east and south East Asia,while the C-mode produces the decreased precipitation over the south of East Asia compared with historical experiment.It can be inferred that the combination effects of ENSO itself and the C-mode contribute to the distribution of the change of precipitation anomaly.During summer time,it shows the cyclone anomaly over the south of China,while the anticyclone appears over the north of the Yangtze River Valley.The 500h Pa high pressure anomaly exists around the tropical western Pacific Ocean,and it moves southward compared with the historical experiment,which reflects the southward shift of the Northwest Pacific subtropical high and may be induced by the weakened convection for tropical Pacific owning to the decreased SSTA over the most regions of tropical Pacific Ocean.The moisture budget term connected with the change of moisture anomaly in response to the high emission scenario during strong EP-El Ni(?)o events contributes to the positive precipitation anomaly over the south of China in the following summer,which is different from that in winter.4.During winter time,the strong EP-El Ni(?)o events shows the larger contribution to the positive skewness for the precipitation anomaly over the north of the Yangtze River Valley and the south of China in the following summer.Based on the experiments from CMIP5 and CFMIP-3,it is found that the high emission could lead to the El Ni(?)o-like SSTA pattern over the tropical regions,and it would induce the positive rainfall over the north of the Yangtze River Valley in winter and the south of China in the following summer,which is similar to the distribution of precipitation anomaly during strong EP events.This could be the results of the larger contribution of the strong EP events to the positive skewness for the precipitation anomaly,and further demonstrates that the strong EP events could have influence on the precipitation change.