基于标准化异常梯度提升算法的集合预报后处理

Post-processing of ensemble forecasts based on the standardized anomalies gradient boosting algorithm

  • 摘要: 近年来,集合预报已成为全球主要天气预报业务中心的重要工具。然而,集合预报常存在离散不足和系统性偏差问题,亟需借助统计后处理方法加以校正。标准化异常模式输出统计(standardized anomalies model output statistics,SAMOS)是常用的统计后处理技术之一,能够刻画预报要素的完整分布特征。然而,SAMOS通常仅依赖与预报量直接相关或基于主观经验选取的因子建模,可能忽略部分潜在的重要预报因子。同时,若直接引入过多预报因子,易导致模型过拟合。因此,如何从多源模式预报因子中有效筛选出关键变量仍是一项挑战。Boosting变量选择与优化算法已被证明在避免过拟合、识别关键因子方面具有良好性能。本文结合SAMOS与Boosting变量选择算法的优势,提出标准化异常梯度提升方法(standardized anomalies gradient boosting,SABST),用于校准2  m温度、2  m相对湿度及10  m风速的集合预报。SABST基于2019—2020年欧洲中期天气预报中心提供的细网格预报与集合预报(ensemble prediction system,ENS)数据建模,并与SAMOS方法进行系统比较,重点评估其在集合预报校准与偏差订正方面的性能。结果表明,相较于ENS与SAMOS,SABST能更有效缓解集合预报中的欠分散问题,并显著提升确定性预报的准确性。以连续分级概率技能得分(continuous ranked probability skill score,CRPSS)为评价指标,对2 m温度,2 m相对湿度,10 m风速的预报,SABST在各预报时效下的平均CRPSS较SAMOS分别提高9.5%、15.3%和4.6%。该结果验证了引入潜在预报因子的有效性,显示出SABST在集合预报后处理中的应用潜力。

     

    Abstract: In recent years, ensemble forecasting has become a vital tool for major global weather forecasting centers. However, ensemble forecasts often exhibit underdispersion and systematic biases, making the application of statistical post-processing methods essential. The standardized anomalies model output statistics (SAMOS) is a commonly used post-processing technique that provides a complete description of the forecast distribution. Nevertheless, SAMOS typically relies only on predictors either directly related to the forecast variable or selected based on subjective judgment, potentially overlooking other valuable predictors. Moreover, directly incorporating too many predictors into SAMOS may lead to overfitting. Therefore, effectively selecting key predictors from numerous variables provided by forecast models remains a significant challenge. Boosting-based variable selection and optimization algorithms have proven to be effective in mitigating overfitting and identifying the most important predictors. This study proposes the standardized anomalies gradient boosting (SABST) method by integrating the strength of SAMOS with a Boosting-based variable selection algorithm. SABST is applied to calibrate ensemble forecasts of 2 m temperature, 2  m relative humidity, and 10  m wind speed. The SABST model is developed using the European Centre for Medium-Range Weather Forecasts (ECMWF) high-resolution ensemble forecast (ensemble prediction system, ENS) products during 2019—2020 and is systematically compared with SAMOS, focusing on its calibration performance and bias correction ability. Results show that compared to ENS and SAMOS, SABST performs better in addressing underdispersion in probabilistic forecasts and improving the accuracy of deterministic forecasts. Based on the continuous ranked probability skill score (CRPSS), SABST improves the average CRPSS by 9.5%, 15.3%, and 4.6% across all forecast lead time compared to SAMOS. These findings demonstrate the advantage of introducing additional potential predictors in the SABST framework and highlight the method's potential for application in ensemble forecast post-processing.

     

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