南海与西北太平洋地区夏季热带气旋潜在生成指数的改进

现阶段使用的热带气旋潜在生成指数(Genesis Potential Index,GPI)在气候场的空间分布上能很好地拟合热带气旋的生成情况,但在热带气旋的年际变化拟合上效果很差。本研究考虑了相对涡度在热带气旋年际变化拟合上的重要作用,并以此为出发点,尝试改善GPI在西北太平洋地区的拟合效果。基于对1979—2011年美国联合飓风警报中心提供的热带气旋最佳路径数据和NCEP/NCAR再分析资料数据集的研究,将之前GPI中的绝对涡度项替换为修正过的相对涡度项。科氏力项仍然保留;将南海(100°～120°E,5°～25°N)与西北太平洋地区(120°～180°E,5°～40°N)热带气旋生成的差异性也纳入了考量,并在这两个区域分别构建GPI公式,改善了对热带气旋生成的气候分布模拟。除此之外,较之已存的GPI指数,改进后的GPI还很大程度提高了GPI对热带气旋生成年际变化的拟合效果,特别是对弱热带气旋年际变化的拟合效果有了显著提升。

Improvement of genesis potential index for western North Pacific tropical cyclones

The previous genesis potential index (GPI) can be applied to accurately simulate the climate distribution of tropical cyclone (TC) genesis,yet performs poorly in the simulation of interannual variation of TC genesis.The present study attempts to improve the GPI over the western North Pacific (WNP),by considering the important impact of relative vorticity on interannual variation of TC genesis.Based on the best-track data from the Joint Typhoon Warning Center and NCEP/NCAR reanalysis data from 1979 to 2011,we substitute the absolute vorticity in the previous GPI with a modified relative vorticity.The Coriolis factor remains intact.The difference of tropical cyclone formation between the South China Sea (SCS) and WNP is also considered,and the GPI for the SCS (5°-25°N,100°-120°E) and WNP (5°-40°N,120°-180°E) are respectively developed.The modified GPI is shown to improve the simulation of the climate distribution of TC genesis.Moreover,compared with the previous GPI,the modified GPI greatly improves the simulation of the interannual variation of TC genesis,in particular in regard to weak tropical cyclones.