| El Ni(?)o-Southern Oscillation(ENSO)is the strongest interannual variability signal in the global climate system.ENSO modulates anomalous convective heating over the tropical Pacific that influences agriculture,ecosystem and global climate system through exciting large-scale teleconnection.Previous studies indicated that the diversity of ENSO-driven precipitation anomalies was associated with the nonlinear response of deep convection to SST.But it seems like this nonlinear relationship cannot totally explain the diversity in zonal distribution of ENSO-driven precipitation anomalies.Furthermore,the eastward shift and extension of ENSOdriven precipitation anomalies under global warming has remained unexplained.In this paper,we develop an analysis method that combines Lindzen-Nigam boundary layer theoretical model and moist static energy(MSE)budget,and systematically investigate ENSO-driven precipitation anomalies over the equatorial central eastern Pacific.First,from the perspective of observation analysis,we reveal the formation mechanisms for the spatial differences in different types of ENSO-driven precipitation anomalies.Second,we propose a new mechanism for the change in ENSO-driven precipitation anomalies under global warming based on a large ensemble of climate prediction experiment of coupled climate model.At last,we discuss the differences of global teleconnection induced by different types of ENSO-driven precipitation anomalies and the change in global teleconnection induced by the change in ENSO-driven precipitation anomalies under global warming.The main conclusions are summarized as follow:(1)The observation analysis indicate that the zonal position of ENSO-driven precipitation anomalies over the equatorial Pacific shows a pronounced diversity that the center of positive precipitation anomalies of eastern-Pacific(EP)El Ni(?)o is located to the east of the positive center of central-Pacific(CP)El Ni(?)o and the negative center of La Ni(?)a.The minimum of negative precipitation anomalies over the equatorial Pacific during La Ni(?)a is located to the west of the maximum of positive precipitation anomalies during CP El Ni(?)o,even though the center of the negative sea surface temperature anomaly(SSTA)for La Ni(?)a is close to(even located slightly to the east of)that of the positive SSTA for CP El Ni(?)o.We systematically analyse the contribution of several physical processes to different types of ENSO-driven precipitation anomalies through combining moisture,moist static energy(MSE)budget and idealized model simulations(Lindzen-Nigam-like model,LN-like model).The results show that the diversity of precipitation anomalies is determined by the boundary layer convergence anomalies which are mainly induced by underlying SST anomalies through the Lindzen-Nigam mechanism,that is,the zonal location of which are mainly controlled by the meridional and zonal distributions of the ENSO SST anomalies.The westward shift of the center of negative precipitation anomalies during La Ni(?)a relative to that of positive precipitation anomalies during CP El Ni(?)o is primarily caused by the combined effects of nonlinear zonal moist enthalpy advection and Lindzen-Nigam mechanism mentioned above.Furthermore,the zonal diversity of precipitation anomalies is further enhanced by three processes,including: the“convection-cloud-longwave radiation” feedback,the SSTA-induced latent heat flux anomalies and “wind-induced moist enthalpy advection” feedback.(2)We also discuss the projected changes in ENSO-driven tropical precipitation anomalies under global warming and further explore the physical mechanisms for such changes.During ENSO mature winter,the change in ENSO-driven tropical precipitation anomalies under global warming shows a zonal dipole distribution,with an enhanced positive precipitation anomalies over the equatorial central-eastern Pacific and an eastward shift and extension,and enhanced negative precipitation anomalies over the tropical western North Pacific(WNP).We show that the eastward shift and extension of the positive pole of precipitation anomalies are caused by following processes: The weakening of the subtropical cell(STC)and associated mean trade wind leads to the narrowing of the meridional span of underlying SST anomalies by reducing poleward advection of anomalous warm water from the equator.This meridional narrowing intensifies the meridional gradient of SST anomalies and enhances the boundary-layer moisture convergence over the equatorial eastern Pacific,and eventually leading to the eastward shift and extension of positive precipitation anomalies.Furthermore,the changes in the mean state(including the increase of moisture content,vertical motions and vertical stratification of MSE)and the positive “convection-cloud-longwave radiation” feedback all have contributions to the intensification of the positive precipitation anomalies.The changes in the positive precipitation anomalies also lead to the intensification and eastward extension of the negative precipitation anomalies over the tropical WNP through strengthening the advection of low moist enthalpy to the western North Pacific.(3)In addition,we discuss the impact of the diversity of ENSO-driven precipitation anomalies and the impact of changes in ENSO-driven precipitation anomalies under global warming.The results show that the diversity of ENSO-driven precipitation anomalies cause the diversity of the zonal position of anomalous Walker Circulation,western North Pacific cyclone(or anticyclone,WNPAC)anomalies and Pacific-North America(PNA)teleconnection.The eastward shift and extension of ENSO-driven tropical precipitation anomalies under global warming lead to the eastward shift of ENSO-induced PNA teleconnection and anomalous Walker Circulation.The enhanced negative precipitation anomalies over the WNP strengthen the WNPAC,which leads to southeastern China becoming wetter during El Ni(?)o mature winter.Meanwhile,El Ni(?)o will decay faster after reaching its peak and shorten its duration under global warming. |
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