CESM2季节到多年集合预报中长时效ENSO预测的前兆、路径与状态依赖可靠性
Precursors, Pathways, and State-Dependent Reliability of Long-range ENSO Prediction in the CESM2 Seasonal-to-Multiyear Large Ensemble
- University of Illinois Urbana-Champaign（伊利诺伊大学厄巴纳-香槟分校）
- NSF National Center for Atmospheric Research (NCAR)（美国国家科学基金会国家大气研究中心）
- North Carolina State University（北卡罗来纳州立大学）
- University of Hawai’i at Mānoa（夏威夷大学马诺阿分校）
机构由 AI 辅助整理，请以论文原文为准。
AI总结：
本研究利用CESM2 SMYLE集合预报和XRO基准，揭示ENSO长时效预测技巧的来源，发现2月初始化依赖Bjerknes反馈和NPMM，8月初始化依赖跨海盆延迟路径，并提出改进初始太平洋状态和跨海盆耦合以提升预测。
AI中文摘要：
理解ENSO预测技巧和误差的来源对于改进长期气候预测至关重要。本文利用集合敏感性分析和扩展非线性充电振荡器（XRO）基准，研究了1970-2019年间CESM2季节到多年大集合（SMYLE）在2月和8月初始化的回报试验中的ENSO前兆。SMYLE表现出有意义的长时效技巧，2月初始化的预测在接下来的冬季仍保持技巧，而8月初始化的预测在16个月后的12月目标仍保留有用技巧。然而，预测在状态依赖的方式下存在分散不足的问题。秩直方图显示，强ENSO事件存在过度自信问题，弱事件则存在暖偏差。2月的可预测性源于经典的Bjerknes反馈动力学，并受到类似于北太平洋经向模态（NPMM）的副热带-热带相互作用的强化。最佳的2月初始化预测在初始化时具有暖的西太平洋次表层异常和拉尼娜异常，此后赤道受限异常和对热带外影响的敏感性相对较弱。8月初始化预测中的第二年ENSO可预测性则通过一种以跨海盆预调节为特征的延迟路径出现。有技巧的案例始于热带赤道南大西洋的冷异常和热带西印度洋的暖异常，而太平洋过程在次年之前作用减弱。SMYLE在两个12月目标上都匹配了交叉验证的XRO技巧，其敏感性与观测拟合的基准一致，尽管大西洋耦合似乎被错误表征。这些发现表明，改进GCM中初始太平洋状态和跨海盆耦合的保真度可能有助于改进ENSO预测。
英文摘要：
Understanding the sources of ENSO prediction skill and error is essential for improving long-range climate prediction. Here we examine ENSO precursors in CESM2 Seasonal-to-Multiyear Large Ensemble (SMYLE) hindcasts initialized in February and August during 1970-2019, using ensemble sensitivity analysis and an extended nonlinear recharge oscillator (XRO) benchmark. SMYLE exhibits meaningful long-lead skill, with February-initialized predictions remaining skillful through the following winter, and August-initialized predictions retaining useful skill at the December target sixteen months ahead. However, the predictions are under-dispersive in a state-dependent manner. Rank histograms reveal overconfidence issues for strong ENSO events and a warm bias for weak events. February predictability arises from canonical Bjerknes feedback dynamics reinforced by subtropical-tropical interactions resembling the North Pacific Meridional Mode (NPMM). The best February-initialized predictions feature warm western Pacific subsurface anomalies and La Nina anomalies at initialization, with equatorially confined anomalies and relatively weak sensitivities to extratropical influences thereafter. Second-year ENSO predictability in August-initialized predictions instead emerges through a delayed pathway characterized by cross-basin preconditioning. Skillful cases begin with a cold tropical equatorial South Atlantic and a warmer tropical western Indian Ocean, while Pacific processes play a reduced role until the following year. SMYLE matches the skill of the cross-validated XRO at both December targets, and its sensitivities agree with the observationally fitted benchmark, though the Atlantic couplings appear misrepresented. These findings suggest that improving the initial Pacific state and cross-basin coupling fidelity in GCMs may help improve ENSO prediction.
