基于EMOS的多种集合预报后处理方法对比研究

Comparison of multiple statistical calibration methods for ensemble forecasting based on the EMOS

  • 摘要: 数值天气预报的系统偏差通常需要后处理校正。EMOS是一种针对集合预报的后处理方法,近年来也逐渐发展出了两种衍生方法(gEMOS、SAMOS)来对它进行改进。因此使用中国气象局的全球集合预报(GEPS)、全球确定性预报(GFS)、区域集合预报(REPS)以及两个不同空间分辨率的中尺度天气数值预报系统(MESO-10 km,MESO-3 km)共5个数值模式,对华北地区2 m气温、2 m相对湿度、10 m风速和3 h累计降水的预报订正效果进行了比较。结果表明,3种模式后处理方法均能有效提升对上述要素的预报效果,订正后的预报误差要小于所有输入的数值预报模式。(1)EMOS站点之间独立计算的方式能使得其保留站点的气候特征,因此在3种方法中预报误差是最小的;(2)gEMOS由于忽略了站点的独立性,因此预报误差要高于EMOS;(3)对SAMOS而言,气温、湿度和风速这些气候态模拟较为准确的要素,预报误差能达到和EMOS相同的水平,而对于降水这类偏态分布的变量,模拟的气候态影响了SAMOS的订正效果,因此SAMOS的预报误差要大于EMOS,但仍小于gEMOS。

     

    Abstract: Systematic biases in numerical weather prediction commonly require post-processing correction. EMOS is a post-processing method for ensemble forecasts. In recent years, two other variations of EMOS (gEMOS and SAMOS) have been proposed to improve EMOS. This paper aims to evaluate their performance. A comparative study has been conducted for 2 m temperature, relative humidity, 10 m wind speed, and 3 h cumulative precipitation in North China using five numerical models, i.e., the Global Ensemble Prediction System (GEPS), the Global Forecast System (GFS), the Regional Ensemble Prediction System (REPS), and two mesoscale weather numerical forecasts (MESO-10 km, MESO-3 km) with different spatial resolutions from the China Meteorological Administration (CMA). Results show that all the three post-processing methods can reduce forecast errors of the CMA models across these variables. Specifically, (1) the EMOS method, which independently calculates parameters for each station, retains the unique characteristics of individual stations, resulting in optimal performance; (2) gEMOS underperforms EMOS due to its neglect of inter-station independence; (3) for variables such as temperature, humidity, and wind speed, which accurately simulate climatological distribution, SAMOS performance is comparable to that of EMOS. For precipitation, SAMOS's performance is constrained by climatological precipitation distribution simulation; the forecast error of SAMOS is larger than that of EMOS, yet it is still smaller than that of gEMOS.

     

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