This study evaluates the prediction skill of the North Atlantic Oscillation (NAO) pattern and its associated energy budget as simulated by the European Center for Medium-Range Weather Forecasts ensemble forecast system. By classifying NAO events into high- and low-skill cases, we analyzed the stationarity of NAO patterns and the role of baroclinic energy conversion in NAO prediction. In both positive and negative NAO phases, high-skill cases exhibited more stationary NAO patterns than low-skill cases. The analysis of processes indicates that high-skill NAO cases are due to stronger baroclinic maintenance of NAO, with its initial position at the climatological thermal trough, whereas low-skill NAO cases result from forecast biases in wave propagation from the North Pacific. Specifically, biases in baroclinic energy conversion in the meridional direction from week 2 lead to weak advection of the eddy available potential energy (EAPE), resulting in lower prediction skill.

中文翻译：

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ECMWF 集合预报系统中亚季节北大西洋涛动预测的过程评价


本研究评估了欧洲中期天气预报中心集成预报系统模拟的北大西洋涛动 （NAO） 模式及其相关能量收支的预测技能。通过将 NAO 事件分为高技能和低技能案例，我们分析了 NAO 模式的平稳性以及斜压能量转换在 NAO 预测中的作用。在正和负 NAO 阶段，高技能案例比低技能案例表现出更多的平稳 NAO 模式。过程分析表明，高技能 NAO 案例是由于 NAO 的强斜压维持，其初始位置位于气候热槽，而低技能 NAO 案例是由于北太平洋波传播的预测偏差造成的。具体来说，从第 2 周开始，斜压能量在经向转换的偏差导致涡流有效势能 （EAPE） 的弱平流，从而导致预测技能降低。