Springtime extra-tropical cyclones in Northeast Asia and their impacts on long-term precipitation trends

Abstract

Springtime extra-tropical cyclones (ETCs) in Northeast Asia and the associated precipitation anomalies are examined by objectively tracking ETCs from reanalysis data. The cluster analyses reveal that Northeast Asian cyclones are largely grouped into two distinct tracks, that is, north and south tracks, depending on their pathways. The south-track ETCs typically form over southeast China and travel towards the Japanese Islands, while the north-track ETCs are first detected around Mongolia and move southeastwards to the Korean Peninsula. Unlike the latter ones, the former ones exhibit a significant negative trend in their occurrence frequency (-1.17 per decade from 1979 to 2014), explaining a negative precipitation trend over the broad regions from southeast China to the Kyushu Islands. It is argued that the reduction of the south-track ETCs is at least in part caused by the strengthened convection over the tropical western Pacific. The resulting Gill-type response in the subtropics tends to drive reduced moisture supplies to southern China, likely causing an unfavourable condition for the development of the south-track ETCs.