Revealing the most disturbing tendency error of Zebiak–Cane model associated with El Niño predictions by nonlinear forcing singular vector approach
Revealing the most disturbing tendency error of Zebiak–Cane model associated with El Niño predictions by nonlinear forcing singular vector approach
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DOI：
10.1007/s00382-014-2369-0
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发表时间：
2015-05
期刊：
影响因子：
4.6
通讯作者：
W. Duan;P. Zhao
中科院分区：
文献类型：
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作者：
W. Duan;P. Zhao
非线性强迫奇异向量（NFSV）的方法被用来确定最令人不安的趋势误差的Zebiak-Cane模式与厄尔尼诺的预测，这是最有可能产生积极的大预测误差的厄尔尼诺事件。结果表明，只有一个NFSV存在的每个预定模式厄尔尼诺事件的预测。在理想初始条件下，这些NFSV对相应的厄尔尼诺事件的预测误差最大。结果表明，NFSV往往呈现大尺度纬向偶极结构，对厄尔尼诺事件的强度不敏感，但依赖于预报周期。特别是，与厄尔尼诺增长阶段的预测交叉的NFSV往往表现出纬向偶极型，赤道中西部太平洋为正异常，赤道东太平洋为负异常（表示为“NFSV 1”）。与此同时，与厄尔尼诺衰减阶段的预测相关联的那些倾向于呈现另一种纬向偶极型（记为“NFSV 2”），这几乎与NFSV 1相反。同样，基于切线性模型计算的线性强迫奇异向量（FSV）也可以分为“FSV 1”和“FSV 2”两种类型。结果表明，FSV 1和NFSV 1对厄尔尼诺事件的Nino-3海表温度异常的预报常出现负误差，而FSV 2和NFSV 2对厄尔尼诺事件的Nino-3海表温度异常的预报常出现正误差。然而，由于非线性的影响，NFSV的纬向偶极模式的西极通常更远，覆盖范围更广。非线性对FSV型趋势误差的增长有抑制作用，而NFSV型趋势误差的特殊结构又会减弱非线性的抑制作用，最终导致NFSV型趋势误差对厄尔尼诺事件的Nino-3海温异常产生较大的预报误差。与FSV相比，NFSV更适用于描述Zebiak-Cane模型中最令人不安的趋势误差，因为它们考虑了非线性的影响。NFSV型趋势误差可以提供关于敏感地区的信息，在这些地区，模式误差更有可能对厄尔尼诺事件产生大的预测误差。如果能提高敏感区国家的模拟能力，则ENSO预报能力也会大大提高。
The nonlinear forcing singular vector (NFSV) approach is used to identify the most disturbing tendency error of the Zebiak–Cane model associated with El Niño predictions, which is most potential for yielding aggressively large prediction errors of El Niño events. The results show that only one NFSV exists for each of the predictions for the predetermined model El Niño events. These NFSVs cause the largest prediction error for the corresponding El Niño event in perfect initial condition scenario. It is found that the NFSVs often present large-scale zonal dipolar structures and are insensitive to the intensities of El Niño events, but are dependent on the prediction periods. In particular, the NFSVs associated with the predictions crossing through the growth phase of El Niño tend to exhibit a zonal dipolar pattern with positive anomalies in the equatorial central-western Pacific and negative anomalies in the equatorial eastern Pacific (denoted as “NFSV1”). Meanwhile, those associated with the predictions through the decaying phase of El Niño are inclined to present another zonal dipolar pattern (denoted as “NFSV2”), which is almost opposite to the NFSV1. Similarly, the linear forcing singular vectors (FSVs), which are computed based on the tangent linear model, can also be classified into two types “FSV1” and “FSV2”. We find that both FSV1 and NFSV1 often cause negative prediction errors for Niño-3 SSTA of the El Niño events, while the FSV2 and NFSV2 usually yield positive prediction errors. However, due to the effect of nonlinearities, the NFSVs usually have the western pole of the zonal dipolar pattern much farther west, and covering much broader region. The nonlinearities have a suppression effect on the growth of the prediction errors caused by the FSVs and the particular structure of the NFSVs tends to reduce such suppression effect of nonlinearities, finally making the NFSV-type tendency error yield much large prediction error for Niño-3 SSTA of El Niño events. The NFSVs, compared to the FSVs, are more applicable in describing the most disturbing tendency error of the Zebiak–Cane model since they consider the effect of nonlinearities. The NFSV-type tendency errors may provide information concerning the sensitive areas where the model errors are much more likely to yield large prediction errors for El Niño events. If the simulation skills of the states in the sensitive areas can be improved, the ENSO forecast skill may in turn be greatly increased.