基于偏最小二乘回归理论的西北太平洋热带气旋强度统计预报方法

A statistical prediction scheme of tropical cyclone intensity over the western North Pacific based on the partial least square regression

  • 摘要: 热带气旋(TC)的强度预报是TC研究中的前沿性问题和实际业务中的难点。当前具有参考价值的预报方法主要是统计类或模式释用类方法,例如气候持续性(CLIPER)模型等。CLIPER模型的核心技术为多元线性回归,这种回归算法在预报因子之间存在多重相关性时会丧失建模的稳健性,进而影响CLIPER模型的预报精度。为了提高CLIPER模型的适用性并且改进预报结果,将第2代统计回归理论——偏最小二乘回归技术引入CLIPER模型中,取代原有的多元线性回归技术,提出了PLSCLIPER模型。比较两种模型2004—2007年的平行预报试验结果,发现PLS-CLIPER模型的TC强度预报趋势一致率和平均绝对误差在72 h以内均优于CLIPER模型,特别是对48 h以内的TC强度预报有较显著的改进(例如12 h的强度预报趋势一致率提高了近10%;平均绝对误差减小了近2 m/s)。PLS-CLIPER模型的预报比CLIPER模型稳定,前者的误差基本不受TC的强度及其变化、TC中心所在经纬度位置和移动速率的影响。此外,PLS-CLIPER模型还显著改进了起报时刻强度在50 m/s以下的TC、处于增强和维持阶段的TC、近海和西/西北行TC的强度预报准确性。结果表明,在CLIPER模型中选用相同物理量作为预报因子的前提下,更加先进合理的统计回归技术可以显著改进预报结果,这为以后在动力统计相结合的统计释用框架下进一步改进TC强度的预报提供了理论和算法基础。

     

    Abstract: Tropical cyclone (TC) track forecast errors have decreased considerably over the past several decades while there have been only modest intensity forecasting improvements, despite that the prediction of tropical cyclone intensity is an important and difficult task for not only scientists but also operational forecasters. In recent years, the best guidance of forecasting TC future intensity is the approach based on the statistical or statisticaldynamical models, such as the CLIPER (Climatology and Persistence) model. Since the multiple linear regression is the kernel technique in the CLIPER model, the statistical model set up by it could be inaccurate and instable when the predictors used to develop the equation are highly correlated with each other. In order to improve the CLIPER model through increasing its stability and decreasing its forecast error, the second generation of regression technique, so-called the Partial Least Square (PLS) regression, is introduced into the CLIPER model in this paper, and the current operational STI-CLIPER model is updated to the PLS-CLIPER model. The PLS-CLIPER and STI-CLIPER models are both applied to forecast TC intensities in the future 120 h over the western North Pacific from 2004 to 2007, and the intensity forecasting results made by them show that the PLS-CLIPER model is superior to the STI-CLIPER model within future 72 h. The prediction of TC intensity at the future 12 h from the PLS-CLIPER model is more accurate than the STI-CLIPER model through increasing the forecast tendency consistent rate by 10% and decreasing the mean absolute forecast error by 2 m/s. Particularly for the fastly intensified TCs whose increase of maximum surface sustained wind surpasses 10 m/s within 12 h, the forecast error from the former is around 4 m/s smaller than that from the latter. Besides these, the forecast model established by the PLSCLIPER model is more stable than the STICLIPER model, and the forecast error made by the former is independent on the TC intensity and its change, TC center position (latitude and longitude), and TC moving speed. Furthermore, the intensity forecasting accuracy is remarkably improved by the PLSCLIPER model for the TCs which include (1) the TC with the initial maximum surface sustained wind less than 50 m/s, (2) the TC that is in the intensified and sustained stages,(3) the TC occurring over the offshore of China, and (4) the TC moving westward or northwestward. These results indicate that, in the CLIPER model of choosing the same samples and potential physical predictors, more reasonable and more advancing technique of regression could lead to a more accurate forecast result. This work is a theoretical and algorithmic search for predicting the TC intensity under the framework of statistical-dynamical models in the future.

     

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