西北太平洋台风活动的年代际变化与大尺度环流因子的关系

用多项式拟合和统计分析的方法对1960～2005年西北太平洋台风年频数资料进行分析表明：台风活动存在明显的年代际变化，46a间台风活动存在两个高频期和两个低频期，高低频期台风频数的差异主要集中在7～10月（称为台风活跃季），利用台风活跃季的NCEP／NOAA资料对影响台风年代际变化的大尺度环流因子进行分析，结果表明：与低频期相比，在台风生成的高频期出现了较高的海表温度、较低的海平面气压、较大的高层散度和低层相对涡度、较小的垂直风切变，而且500hPa风场利于台风的生成和向西北太平洋移动。西太平洋副热带高压偏北，100hPa南亚高压偏弱。西北太平洋海盆的总降水量的年代际变化与台风的年代际变化关系不明显。

LARGE SCALE CIRCULATION ASSOCIATED WITH INTERDECADAL VARIATIONS OF TYPHOON ACTIVITY OVER THE WESTERN NORTH PACIFIC

Based on the Typhoon(TY) frequency data of Tropical Cyclone Yearbooks from 1960 to 2005,TY frequency of 46a has exhibited obvious decadal-scale variability by the polynomial fit and statistical analysis.And it has two high frequency periods(HFP) and two low frequency periods(LFP).Significant differences in the number of TYs between HFP and LFP are found in the TY activity season from July through October.Differences of large-scale circulation during HFP and LFP are investigated with NCEP/NOAA data of TY activity season.In HFP,the condition includes not only high sea surface temperature,low sea level pressure,large divergence of upper air,large relative vorticity of low level and small vertical shear,but also favorable 500-hPa wind vector for TY activity and movement to western North Pacific,northward positions of the subtropical anticyclone over the western Pacific,and a South Asian anticyclone at 100hPa much smaller than in LFP.The precipitation of western North Pacific has no clear influence on TY activity.