GRAPES区域集合预报两种侧边界扰动方法对比试验

Comparison of Two Lateral Boundary Perturbation Methods in the Regional Ensemble Prediction System of GRAPES

中国气象局数值预报中心自2014年建立了区域集合预报业务系统,其使用的侧边界扰动由全球集合预报系统动力降尺度得到。为深入了解侧边界扰动对区域集合预报的影响,基于15 km水平分辨率的区域集合预报模式,使用动力降尺度方法和尺度化滞后平均法(scaled lagged average forecasting,SLAF)设计构造了两种侧边界扰动方案,并开展了2015年7月共6天的集合预报试验,利用集合均方根误差、集合离散度、连续分级概率评分、离群值、Brier Score及相对作用特征曲线面积等概率预报检验方法进行了多方面检验,分析了两种侧边界扰动方案对区域集合预报质量的影响。结果表明:动力降尺度侧边界扰动方案(DOWN)的扰动总能量在各垂直层次均大于SLAF方案,使得边界上前者的离散度大于后者,集合扰动增长更为合理;对于等压面要素和地面要素,DOWN方案的离散度、Outlier、CRPS等评分优于SLAF方案,反映了DOWN方案构造的侧边界扰动更加合理;在降水概率预报技巧方面,SLAF方案在评分上具有一定优势,但评分的提高没有通过显著性水平检验,因此认为两种方案对降水预报的改进基本相当。

The China Meteorological Administration Numerical Weather Prediction Centre has established the GRAPES-REPS(Global and Regional Assimilation and Prediction Enhanced System-Regional Ensemble Prediction System)business system since 2014.The lateral boundary perturbation is obtained by the global ensemble prediction system.In order to understand the impact of lateral boundary perturbation on GRAPES regional ensemble prediction,this paper,based on the GRAPES-REPS regional ensemble prediction model with 15 km horizontal resolution,constructed two lateral boundary perturbation schemes using the scaled lagged average forecasting(SLAF)method and the dynamic downscaling method.Two kinds of lateral boundary perturbation experiments were designed.The 6 d ensemble prediction test was carried out in July 2015.Using root mean square error(RMSE),spread,CRPS,Outlier,Brier score,TS,AROC and other probabilistic forecast test,the impacts of the two kinds of lateral boundary perturbation methods on the regional ensemble prediction quality were analyzed.The results showed that the energy of the lateral boundary perturbation obtained by dynamic downscaling(DOWN)is greater than that of the SLAF experiment at each vertical layer,resulting in the spread of DOWN experiment greater than the dispersion of SLAF experiment.For the isobaric elements and the ground elements,the scores of DOWN experiment are better than the scores of SLAF experiment,indicating that the lateral boundary perturbation of the DOWN experiment structure is more reasonable.In the aspect of precipitation probability prediction skill,the SLAF experiment has certain advantages in scoring,but the improvement of the score does not pass the significance test,so the two experiments are considered to be similar in the improvement of precipitation forecast.