The equatorial Pacific cold tongue bias in CESM1 and its influence on ENSO forecasts
The equatorial Pacific cold tongue bias in CESM1 and its influence on ENSO forecasts
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DOI：
10.1175/jcli-d-21-0470.1
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发表时间：
2022-02
影响因子：
4.9
通讯作者：
Xiandu Wu;Y. Okumura;S. Yeager;C. Deser;P. DiNezio
中科院分区：
文献类型：
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作者：
Xiandu Wu;Y. Okumura;S. Yeager;C. Deser;P. DiNezio
在1954 - 2015年社区地球系统模式第1版进行的一套两年期超前回顾预报中，研究了厄尔尼诺-南方涛动（ENSO）的平均状态偏差和相关预报误差。由于模式固有的气候偏差、初始化不平衡和初始海洋数据的错误，预测中的赤道太平洋冷舌过于强大，并过度向西延伸。预报显示，由于初始次表层海洋状态和模式动力学之间的不平衡，第一年的冷舌偏置比模式固有的偏置更强。冷舌偏差不仅影响预报中ENSO的模式和幅度，而且通过改变海洋-大气反馈来影响ENSO的持续时间。在北半球夏季，当冷舌偏置较强时，与ENSO相关的海温异常可扩展到赤道远西太平洋，而在赤道中东部太平洋，ENSO异常则较弱。模式和振幅的预报误差通过影响ENSO成熟期赤道太平洋温跃层负反馈和热带海盆间调整的振幅，进而导致ENSO相变的预报误差。这些ENSO预报误差进一步降低了冬季大气遥相关、陆面气温和北方半球降水异常的预报。这些平均状态和ENSO的预测偏差更明显的预测在北方春夏季比其他季节由于季节性强化的Bjerknes反馈。
The mean-state bias and the associated forecast errors of the El Niño-Southern Oscillation (ENSO) are investigated in a suite of two-year lead retrospective forecasts conducted with the Community Earth System Model, version 1 for 1954-2015. The equatorial Pacific cold tongue in the forecasts is too strong and extends excessively westward due to a combination of the model’s inherent climatological bias, initialization imbalance, and errors in initial ocean data. The forecasts show a stronger cold tongue bias in the first year than that inherent to the model due to the imbalance between initial subsurface oceanic states and model dynamics. The cold tongue bias affects not only the pattern and amplitude but also the duration of ENSO in the forecasts by altering ocean-atmosphere feedbacks. The predicted sea surface temperature anomalies related to ENSO extend to the far western equatorial Pacific during boreal summer when the cold tongue bias is strong, and the predicted ENSO anomalies are too weak in the central-eastern equatorial Pacific. The forecast errors of pattern and amplitude subsequently lead to errors in ENSO phase transition by affecting the amplitude of the negative thermocline feedback in the equatorial Pacific and tropical interbasin adjustments during the mature phase of ENSO. These ENSO forecast errors further degrade the predictions of wintertime atmospheric teleconnections, land surface air temperature, and rainfall anomalies over the Northern Hemisphere. These mean-state and ENSO forecast biases are more pronounced in forecasts initialized in boreal spring-summer than other seasons due to the seasonal intensification of the Bjerknes feedback.