Using tropical cyclone (TC) observations over a 58-yr period (1949-2006) from the China Meteorological Administration, the 40-year ECMWF Reanalysis (ERA-40), NCEP-NCAR reanalysis, and the Hadley Centre sea ice and sea surface temperature (HadISST) datasets, 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 wintertime 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 parabolic-track-type TCs is found to be decreasing. It is shown that negative sea surface temperature anomalies (SSTAs) related to La Ni a events in the equatorial central Pacific facilitate more TC genesis in the WNP region. Large-scale anomalous cyclonic circulations in the tropical WNP in the lower troposphere are observed to be favorable for cyclogenesis in this area. On the contrary, the positive SSTAs and anomalous anticyclonic circulations that related to El Ni o 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 display an increasing trend in the equatorial eastern-central Pacific. These climate trends of both atmospheric circulation and SSTAs affect wintertime TCs, inducing fewer TC occurrences and causing more TCs to move westward.
HE Jie-LinGUAN Zhao-YongQIAN Dai-LiWAN Qi-LinWANG Li-Juan
全球有限区通用数值预报模式是21世纪数值预报模式的发展趋势,为此"十五"期间中国气象局发展了一个GRAPES(global/regional assimilation and prediction system)全球有限区多尺度非静力数值预报模式.为了验证GRAPES模式方案设计的科学性、程序编写的正确性,针对模式的特点设计了一套完整的理想试验方案来对GRAPES动力模式的性能进行检验,包括用于检验中尺度模式的密度流和三维地形波试验;用于检验近极地半拉格朗日上游点和极区离散方案正确性的越极地气流试验等.密度流试验显示模式框架对精细尺度的非线性流及其瞬变特征有较强的模拟能力;三维地形波试验说明GRAPES模式动力框架能够较好地模拟气流过山时重力内波的水平与垂直传播.而越极地气流试验验证了模式对极地半拉格朗日上游点及近极地的离散处理是正确的.实际个例试验表明,GRAPES全球模式对影响中国夏季的大尺度环流形势有较好的预报能力.
