LAUSR

In this study, the nonlinear local Lyapunov exponent (NLLE) approach was used to quantitatively determine the predictability limit of tropical cyclone (TC) tracks based on observed TC track data obtained from the Joint Typhoon Warning Center. The results show that the predictability limit of all TC tracks over the whole western North Pacific (WNP) basin is about 102 h, and the average lifetime of all TC tracks is about 174 h. The predictability limits of the TC tracks for short-, medium-, and long-lived TCs are approximately 72 h, 120 h, and 132 h, respectively. The predictability limit of the TC tracks depends on the TC genesis location, lifetime, and intensity, and further analysis indicated that these three metrics are closely related. The more intense and longer-lived TCs tend to be generated on the eastern side of the WNP (EWNP), whereas the weaker and shorter-lived TCs tend to form in the west of the WNP (WWNP) and the South China Sea (SCS). The relatively stronger and longer-lived TCs, which are generated mainly in the EWNP, have a longer travel time before they curve northeastwards and hence tend to be more predictable than the relatively weaker and shorter-lived TCs that form in the WWNP region and SCS. Furthermore, the results show that the predictability limit of the TC tracks obtained from the best-track data may be underestimated due to the relatively short observational records currently available. Further work is needed, employing a numerical model to assess the predictability of TC tracks.摘 要非线性局部 Lyapunov 指数 (NLLE) 方法为定量估计大气可预报性提供了一个有效的方法. 在本文研究中, 主要采用美国联合台风警报中心(JTWC)热带气旋最佳路径数据集, 然后利用 NLLE 方法定量研究了西北太平洋热带气旋路径的可预报性. 结果表明: 西北太平洋热带气旋路径的总体平均可预报期限为 ∼108 小时(约 4.5 天). 热带气旋可预报期限的空间分布可以发现, 西北太平洋热带气旋路径的可预报期限大约在 48–120 小时, 且其可预报期限空间分布从东南向西北逐渐降低. 进一步研究发现, 热带气旋的可预报性随源地, 持续时间及强度的变化而有一定的差异. 南海生成的热带气旋可预报期限最小, 随着源地自西向东可预报期限逐渐增大, 西北太平洋东部源地的可预报期限最大; 短生命史的热带气旋可预报期限最小, 随着生命史的增长, 可预报期限逐渐增大; 热带低压的可预报期限最小, 热带风暴和台风的可预报期限大小相当, 强台风的可预报期限最大, 即强度越大, 其可预报期限可能越大. 上述研究结果有助于深入认识和了解热带气旋路径可预报性及其可能影响因子, 对进一步完善目前的热带气旋数值预报模式和提高热带气旋的预报水平有重要科学意义.