The Impact Of El Nino Diversity On East Asian Precipitation And Its Mechanis

At interannual timescale,El Ni(?)o-Southern Oscillation(ENSO)is the dominant air-sea coupling signal,and it exerts profound impact on East Asian climate through an anomalous western North Pacific anticyclone(WNPAC).The characristics of El Ni(?)o have changed in recent decades,understanding the impact of different types of El Ni(?)o on East Asian climate is required.Based on the observational analyses and numerical expriments,this study investigates the mechanism for the different responses of East Asian winter precipitation to eastern Pacific(EP)and central Pacific(CP)El Ni(?)o.The different East Asian precipitation anomaly is compared in super and regular El Ni(?)o decaying summers,besides,the mechanisms for the distinctive monthly evolution of East Asian summer precipitaton in two types of El Ni(?)o is further investigated.The main conclusions are summarized as follows:(1)Increased rainfall appears over East Asia during EP El Ni(?)o winter,while no significant change is found during CP El Ni(?)o winter.The different East Asian rainfall is primarily attributed to the different behavior of the anomalous WNPAC in EP and CP El Ni(?)o winters,which results from the different precipitation anomaly over the WNP,namely the negative precipitation anomaly in EP El Ni(?)o group is stronger and shows a larger spatial scale than that of CP El Ni(?)o.Budget analyses demonstrated that the intensity and spatial scale of the anomalous moist enthalpy advection over the WNP largely modulates the local pecipitaiton anomaly.Compared to CP El Ni(?)o,the positive precipitation anomaly over the equatorical Pacific is enhanced and shifts eastward in EP El Ni(?)o winter,which leads to a strengthened and eastward shift of the triggered northerly anomalies.The negative moist enthalpy advection induced by stronger northerly anomalies is enhanced and shows a larger spatial scale over the WNP in EP El Ni(?)o winter,which finally influences local negative precipitation anomaly.The result of numerical expriment further verifies the dominant role of the atmospheric internal processes associated with the wind-moist enthalpy in causing the different anomalous WNPAC between EP and CP Ni(?)o group,and the contribution of local air-sea coupling process is smaller.(2)Significant positive rainfall anomaly occurs over the Yangtze River Valley in super El Ni(?)o decaying summer,while the positive rainfall anomaly becomes weaker and shifts northward in the regular El Ni(?)o composite.Observational analyses show that the anomalous WNPAC is stronger and shifts southward in super El Ni(?)o decaying summer,which explains the different East Asian rainfall between super and regular El Ni(?)o groups.The different intensity and meridional extent of the anomalous WNPAC between super and regular El Ni(?)o groups is attributed to different intensity of positive sea surface temperature anomaly(SSTA)both over Indican Ocean(IO)and tropical North Atlantic(TNA),with a larger amplitude in super El Ni(?)o group.The results of numerical experiments show that the intensity of anomalous WNPAC is mainly affected by the IO warming in in both super and regular El Ni(?)o groups.Modulated by mean state precipitation,the convection shifts southward over IO,and the convection moves eastward over the TNA in super El Ni(?)o group than that in regular El Ni(?)o group,which leads to a southward movement of the WNPAC.(3)Increased rainbands progress northward in East Asia from June to August during regular El Ni(?)o decaying summer,while strengthened rainbands are only observed in earlier summer and disappear in August in the super El Ni(?)o composite.Observational analyses and the result of numerical experiments demonstrate that the monthly evolving mean state is more important,while the anomalous forcing also plays a role in causing the northward progression of the rainbands in regular El Ni(?)o group.The distinctive rainfall evolution in super El Ni(?)o group is primarily contributed by the 1982/83 and 2015/16 events,whereas the rainband evolution in 1998 resembles the regular El Ni(?)o composite.A cyclonic(anticyclonic)anomaly appears southern Japan in August 1983 and 2016(1998),inducing northerly(southerly)anomalies and thus suppressed(enhanced)rainfall in East Asia.Whereas an anomalous anticyclone in the WNP is a typical response to an El Ni(?)o,the formation of a cyclonic anomaly in the WNP results from anomalous enthalpy advection associated with the eastward retreat of an anomalous anticyclone triggered by a local cold SSTA belt in August 1983 and from a Pacific meridional mode(PMM)-like positive SSTA pattern in August 2016.