The present study compares the contributions of seasonal, intraseasonal, and synoptic variations of environmental factors, i.e., mid-level moisture, vertical instability, and lower-level relative vorticity, to the interannual variation of tropical cyclone (TC) genesis over the western North Pacific (WNP) during July-August-September-October (JASO) of 1979–2015. It is found that the TC genesis frequency has a significant positive correlation with the intensity of intraseasonal oscillation, but a weak correlation with the intensity of synoptic variation of environmental factors during JASO in the WNP. In addition, the intraseasonal components of convection and lower-level vorticity at the location of TC genesis have a larger contribution than the interannual and synoptic components to the differences between more and less TC years over the WNP. The present results indicate that the intensity of intraseasonal oscillation of environmental factors has an important effect on the interannual variation of the TC genesis frequency over the WNP. This study enhances our understanding of the impacts of intraseasonal oscillation on the interannual variation of the WNP TC activity and indicates that the intensity of intraseasonal oscillation has the potential to be used in the seasonal prediction of the WNP TC genesis.

本研究比较了环境因素的季节性、季节内和天气变化，即中层水分、垂直不稳定和低层相对涡度，对西北地区热带气旋 (TC) 成因的年际变化的贡献。 1979-2015 年 7-8-9-10 月 (JASO) 期间的太平洋 (WNP)。研究发现，台风发生频率与季内振荡强度呈显着正相关，与西北部JASO期间环境因子的天气变化强度呈弱相关。此外，与年际和天气成分相比，台风发生位置的对流和低层涡度的季节内分量对西北部台风年份多与少之间的差异有更大的贡献。目前的研究结果表明，环境因子的季节内振荡强度对西太平洋地区台风发生频率的年际变化具有重要影响。该研究加深了我们对季节内振荡对西太平洋热带气旋活动年际变化影响的认识，并表明季节内振荡的强度有可能用于西太平洋热带气旋成因的季节预测。