Recent Northern Hemisphere mid-latitude medium-range deterministic forecast skill
Recent Northern Hemisphere mid-latitude medium-range deterministic forecast skill
复制标题
近期北半球中纬度中程确定性预报技术
DOI：
10.3402/tellusa.v64i0.17531
复制
发表时间：
2012
期刊：
影响因子：
--
通讯作者：
R. Maue
中科院分区：
文献类型：
--
作者：
R. Langland;R. Maue
摘要建立了一个全球确定性预报和分析的多模式档案库，分析了2007 - 2012年北方半球中纬度预报技术及其与北极涛动（AO）指数定义的大尺度大气流量异常的关系。我们发现，异常相关系数（ACC）在120小时预报的500 hPa位势高度在天气，每月和季节的时间尺度上有类似的变化，在这里检查的三个预报系统：欧洲中期天气预报中心，国家环境预测中心全球预报系统，和美国海军业务全球大气预报系统。结果表明，由ACC衡量的预报技巧与AO指数及其负位相和正位相之间的转换显着相关。在2009-2010年和2010-2011年冬季期间，ACC技能异常高的时间间隔与AO保持持续负相位模式的时期有关。低ACC的发作，包括所谓的“预测技能脱落”，最常发生在负和正AO指数之间的过渡期间以及正AO指数。120小时500 hPa高度预报的均方根误差（RMSE）也受AO指数的调制，但幅度小于ACC。在最近两个冬季，RMSE表明在AO指数为负的时期，120小时预报精度较低，这与ACC提供的“技能”模式相反。这些结果表明，ACC并不是在所有情况下都是量化的最佳指标模式预报技巧，因为当大尺度大气流包含强异常时，即使在该大气状态的模式预报中没有实际改进，ACC也可以更高。
ABSTRACT A multi-model archive of global deterministic forecasts and analyses from three operational systems is constructed to analyse recent Northern Hemisphere mid-latitude forecast skill from 2007 to 2012 and its relation to large-scale atmospheric flow anomalies defined by the Arctic Oscillation (AO) index. We find that the anomaly correlation coefficient (ACC) in 120-hr forecasts of 500 hPa geopotential height has similar variability on synoptic, monthly, and seasonal time scales in each of the three forecast systems examined here: the European Centre for Medium-Range Weather Forecasts, the National Centers for Environmental Prediction Global Forecast System, and the U.S. Navy Operational Global Atmospheric Prediction System. The results indicate that forecast skill as measured by the ACC is significantly correlated with the AO index and its transitions between negative and positive phase. Intervals of exceptionally high ACC skill during the 2009–2010 and 2010–2011 winters are associated with periods in which the AO remained in a persistent negative phase pattern. Episodes of low ACC, including so-called ‘forecast skill dropouts’ most frequently occur during transitions between negative and positive AO index and with positive AO index. The root mean square error (RMSE) of 120-hr forecast 500 hPa height is also modulated by the AO index, but to a lesser extent than the ACC. In two recent winters, the RMSE indicates lower 120-hr forecast accuracy during periods with negative AO index, which is opposite to ‘skill’ patterns provided by the ACC. These results suggest that the ACC is not in all situations an optimal metric with which to quantify model forecast skill, since the ACC can be higher when the large-scale atmospheric flow contains strong anomalies even if there is no actual improvement in model forecasts of that atmospheric state.