Impacts Of East Asian Winter Monsoon On Climate Over East Asia And The Western North Pacific

The present study investigates the independent impacts of the East Asian winter monsoon(EAWM)and El Ni(?)o-Southern Oscillation(ENSO)on winter climate over East Asia and the western North Pacific(WNP)and the underlying physical mechanism.This study also evaluates CMIP6 models’ capability of simulating the ENSO-EAWM relationship.The main results are summarized as follows.There exists a south-north dipole pattern of precipitation anomalies in boreal winter over East Asia and the WNP in both the observations and numerical model simulations.Both EAWM and ENSO contribute to the above south-north dipole pattern of precipitation anomalies.In comparison,EAWM has a larger impact on the subtropical precipitation anomalies and ENSO has a larger contribution to the tropical precipitation anomalies.The anomalous EAWM induces an anomalous overturning circulation that links precipitation anomalies between the tropical and mid-latitude regions.A moisture budget diagnosis shows that the dynamic effect associated with vertical motion is dominant in the formation of the tropical precipitation anomalies.Both the dynamical term and the horizontal transport of moisture contribute to the formation of subtropical precipitation anomalies.Surface evaporation has a cancelling effect for subtropical precipitation anomalies.The thermodynamic term associated with the vertical geadient of moisture has a small contribution to both tropical and subtropical precipitation anomalies.Both EAWM and ENSO contribute to the interannual variation of the South China Sea(SCS)cold tongue(CT)intensity.The main terms that contribute to sea surface temperature(SST)anomalies in the CT region are different in different types of years.During years with ENSO alone or with co-existing ENSO and anomalous EAWM,shortwave radiation and ocean horizontal advection play major roles in the interannual change of the SCS CT intensity.In strong CT years with anomalous EAWM alone,surface wind-related latent heat flux has a major role and shortwave radiation is secondary to the EAWM-induced change of the SCS CT intensity.The large contribution of latent heat flux to the CT intensity change in anomalous EAWM alone years is due to that anomalous winds are aligned with climatological mean winds.The relationship between ENSO and EAWM varies largely in CMIP6 models.Nevertheless,most models are still capable of capturing the negative relationship between winter Ni(?)o3.4 SST and EAWMI.The models’ ability of simulating the ENSO-EAWM relationship is largely dependent upon: 1.The longitudinal extension of ENSO-related equatorial Pacific SST anomalies;2.The SST anomalies in the tropical WNP.The influence of the amplitude of ENSO on the simulation of the ENSO-EAWM relationship depends on the westward extension of ENSO-related equatorial Pacific SST anomalies.