Extended Abstract

THE IMPACT OF NORTH PACIFIC SUBTROPICAL HIGHS UPON ENSOON THE INTERANNUAL TIMESCALELI Yi 1 , YANG Xiu-qun 2 , HUANG Shi-cheng 1(1. Jiangsu Institute of Meteorological Sciences, Nanjing 210008, China;2. Institute of Severe Weather and Climate, Nanjing University, Nanjing 210093, China)E-mail: judyliyi@sohu.comAbstractAlong the subtropics of the Northern and Southern Hemispheres, there exist belts of thesubtropical highs. Due to the sea-land terrains, the belts of subtropical high usually split intoseveral cells, and the cells are named subtropical highs. They dominate the activities of thesubtropical synoptic systems and locate between the tropical easterlies and mid-latitudewesterly. They are the ligament of the interaction between the tropical and extra-tropicalcirculation system. Some researchers [1-3] suggest that the anomalous subtropical high can leadto abnormal weather and climate, and it’s closely related with the monsoon, precipitation,ENSO events, and so on [4,5] . ENSO is the strongest signal [6] of interannual climate variabilityin the tropical Pacific and has an important impact upon the global interannual climatevariability [7,8] . ENSO events are often associated with the anomalous wind in the subtropicaltrade-wind zone [9] , so they are also have very close relationship with the subtropical highsystem north of the trade-wind zone. In our preliminary study, we also find that the NorthPacific subtropical high can impact on ENSO and trigger the occurrence of ENSO events.In this paper, by using NCEP atmospheric reanalysis data, Hadley center sea surfacetemperature, and SODA6 oceanic reanalysis data from UMD (University of Maryland),contraposing the whole North Pacific subtropical high system, we first define several indiceswhich quantitatively describe the 500 hPa subtropical high and the SLP subtropical high toanalyze the interannual variations of the 500 hPa subtropical high and the SLP subtropicalhigh. Then, we reveal the characteristics of the anomalous SLP subtropical high leadingENSO events and its triggering role for the establishment of an ENSO event on theinterannual timescale. Results show that on the interannual timescale, the precedinganomalous SLP subtropical high can trigger the occurrence of ENSO events, and theanomalous surface wind field over the western tropical Pacific associated with the SLPsubtropical high plays an important role during the above process by using the methods ofcorrelation and composition.In Fig 1a, we can know that when SLP subtropical high becomes weak, thecorresponding summertime SLP weakens and a cyclonic circulation appears. The subtropicaltrade wind south of the subtropical high also becomes weak. The strong northwest windappearing in the western Pacific subtropical high region will influence this area along withthe abnormal westerly in the western tropical Pacific. The abnormal westerly may cause thewestern equatorial Pacific thermocline to deepen, and spread eastward in the form of Klevinwave, causing the SST in eastern equatorial Pacific to arise and the warm SST to develop.Finally, a matured El Nino (DJF(0)) event forms in winter. Comparing the Fig. 1b with Fig.-427-