Occurrences of Wintertime Tropical Cyclones in the Western North Pacific under the Background of Global Warming

Abstract

Using tropical cyclone (TC) observations over a 58-yr period (1949−2006) from the China Meteorologi- cal Administration, the 40-year ECMWF Reanalysis (ERA-40), NCEP-NCAR reanalysis, and the Hadley Cen- tre sea ice and sea surface temperature (HadISST) data- sets, the authors have examined the behaviors of tropical cyclones (TCs) in the western north Pacific (WNP) in boreal winter (November-December-January-February). The results demonstrate that the occurrences of winter- time TCs, including super typhoons, have decreased over the 58 years. More TCs are found to move westward than northeastward, and the annual total number of para- bolic-track-type TCs is found to be decreasing. It is shown that negative sea surface temperature anomalies (SSTAs) related to La Nina events in the equatorial cen- tral Pacific facilitate more TC genesis in the WNP region. Large-scale anomalous cyclonic circulations in the tropi- cal WNP in the lower troposphere are observed to be fa- vorable for cyclogenesis in this area. On the contrary, the positive SSTAs and anomalous anticyclonic circulations that related to El Nino events responsible for fewer TC genesis. Under the background of global warming, the western Pacific subtropical high tends to intensify and to expand more westward in the WNP, and the SSTAs dis- play an increasing trend in the equatorial eastern-central Pacific. These climate trends of both atmospheric circula- tion and SSTAs affect wintertime TCs, inducing fewer TC