Role of tropical cyclones over the western North Pacific in the East Asian summer monsoon system

摘要

Precipitation observations collected at weather stations in eastern China, the NCEP/NCAR reanalysis data, the tropical cyclone(TC) Best Track Dataset, and a sensitivity numerical experiment were used in the present study to investigate the role in the East Asian summer monsoon(EASM) system played by frequent TC activities over the western North Pacific(WNP). Results indicated that, in active TC years, the EASM is stronger and the southerly winds in the lower troposphere advance farther north and reach higher latitudes.Meanwhile, the monsoon rain belt remains in the lower and middle reaches of the Yangtze River valley for a relatively short period,leading to less precipitation there. Both the western Pacific subtropical high and the South Asian high weaken with the northward shift of the ridgelines for both high-pressure systems as well as the East Asian subtropical upper-level jet. Therefore, the impacts of frequent TC activities over the WNP on each individual component of the EASM are in phase with those of the stronger EASM itself, amplifying features of the already strengthened EASM.