Characteristic large-scale circulation anomalies associated with persistent features of extreme precipitation over northeast Asia from premonsoon season to monsoon season

Characteristic patterns of atmospheric circulation anomalies over the northeast Asian region in the dry and wet premonsoon seasons were analyzed here. The relationship between these patterns in the premonsoon season and the precipitation anomalies in the monsoon season was also investigated. The persistent features of extreme precipitation over northeast Asia from premonsoon season to monsoon season have been found. In order to understand some characteristics of the circulation anomalies associated with persistent features of extreme precipitation, six dry cases and six wet cases in the premonsoon season were selected. Both of the extreme conditions were nearly persistent in each case. For the dry cases, the weakened western North Pacific subtropical high (WNPSH) and the southward-shifted east Asian westerly jet (EAWJ) were predominant. For the wet cases, the strengthening of WNPSH, the northward-shifted EAWJ in spring, and southward-shifted EAWJ in summer were apparent. However, dry cases are associated with the warm sea surface temperature (SST) anomalies of the tropical western Pacific, whereas wet cases are associated with the warm SST anomalies of the Indian Ocean and Bay of Bengal. The dependency of extreme precipitation on these SST anomalies is supported through numerical experiments. In addition, some mechanisms of the persistent features of extreme precipitation are suggested.