[1] We investigate the relationship between the East Asian winter monsoon (EAWM) andsynoptic eddy activity over the North Pacific Ocean. It is well known that the subtropicalPacific jet becomes stronger during strong monsoon periods than during weak monsoons.The storm track is generally expected to be active when the EAWM is strong, owing to the enhanced subtropical jet. Contrary to this expectation, synoptic eddy activity issignificantly reduced in strong EAWM years and, conversely, significantly increasedduring weak years. In addition, we found that EAWM-induced lower level cooling bringsabout the reverse relationship: a stronger jet but with weaker storm activities. It issuggested that the local baroclinicity induced by the EAWM modulates the variation ofboth the jet and North Pacific storm track simultaneously in the interannual time scale.Because major lower level cooling is located in the western parts of both thesubtropical jet and the storm track in longitudes and between the two central axes inlatitudes, it induces the opposite sign of anomalous local baroclinicity at the two activeregions and causes this reverse relationship. The wave seeding from East Asia tothe North Pacific storm track is weakened owing to the anomalous lower level coolingin the northwestern Pacific, which also results in reduction of eddy generation andstorm track activities.
展开▼
