Interannual Variation Of The Western Ridge Point Of The Western Pacific Subtropical High In Winter

This study investigated the interannual variation of the westward ridge point(WRP)of the western Pacific subtropical high(WPSH)in boreal winter with multiple reanalysis and model datasets,including the ERA-Interim provided by European Centre for Medium-Range Weather Forecast(ECMWF),the GPCP precipitation reanalysis provided by the National Oceanic and Atmospheric Administration(NOAA),the global SST(Had ISST)data provided by the Hadley centre(Met Office),the ni(?)o3.4 index provided by the National Center for Atmospheric Research(NCAR),and the hindcasts data from the IFM-GEOMAR coupled ocean-atmosphere general circulation model.Based on the results of statistical diagnosis and numerical simulation,we obtained the following main conclusions:(1)The WRP in winter manifested a remarkable interannual variability,in which the eastward recession(westward expansion)was usually accompanied by northward uplift(southward shift).(2)The interannual variability of the winter WRP was closely related to ENSO.During the cold ENSO events,the negative sea surface temperature anomalies(SSTAs)in the equatorial central–eastern Pacific induced a low-level anticyclonic anomaly over the north Pacific region through the Gill-Matsuno mechanism.Likewise,the positive SSTAs excited a low-level cyclonic anomaly over the northern Philippines.This paired cyclonic–anticyclonic configuration facilitated the northward uplift and the eastward recession of the WPSH.During the warm ENSO events,the SSTAs pattern was almost the opposite over the tropical Pacific and so did the atmospheric response.(3)The interannual variation of the WRP was closely related to the variations in temperature and precipitation over the East Asia–western Pacific region.When the WRP was positioned farther northeastward,the air temperature decreased in the northeastern and southern China,associated with a meridionally "positive–negative" dipole of precipitation anomalies over the mainland China.Conversely,when the WRP was displaced farther southwestward,positive air temperature anomalies appeared in the northeastern and southern China,accompanied with a meridionally "negative and positive" dipole of precipitation anomalies in mainland China.(4)The WRP interannual variation derived from the hindcast result of the IFM-GEMAR ocean-atmosphere coupled general circulation model was relatively accurate.