The Southern Annular Mode (SAM) plays an important role in regulating Southern Hemisphere extratropical circulation. State-of-the-art models exhibit intermodel spread in simulating long-term changes in the SAM. Results from Atmospheric Model Intercomparison Project (AMIP) experiments from 28 models archived in CMIP5 show that the intermodel spread in the linear trend in the austral winter (June–July–August) SAM is significant, with an intermodel standard deviation of 0.28 (10 yr)−1, larger than the multimodel ensemble mean of 0.18 (10 yr)−1. This study explores potential factors underlying the model difference from the aspect of extratropical sea surface temperature (SST). Extratropical SST anomalies related to the SAM exhibit a dipole-like structure between middle and high latitudes, referred to as the Southern Ocean Dipole (SOD). The role of SOD-like SST anomalies in influencing the SAM is found in the AMIP simulations. Model performance in simulating the SAM trend is linked with model skill in reflecting the SOD-SAM relationship. Models with stronger linkage between the SOD and the SAM tend to simulate a stronger SAM trend. The explained variance is about 40% in the AMIP runs. These results suggest improved simulation of the SOD-SAM relationship may help reproduce long-term changes in the SAM.

中文翻译：

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南方冬季南方环状模态模拟长期变化的模式间多样性：南大洋偶极子的作用

南环模态（SAM）在调节南半球温带环流方面发挥着重要作用。最先进的模型在模拟 SAM 的长期变化时表现出模型间传播。来自 CMIP5 中存档的 28 个模式的大气模式比对项目 (AMIP) 实验的结果表明，南方冬季（6 月-7 月-8 月）SAM 线性趋势中的模式间扩展是显着的，模式间标准偏差为 0.28（10 年） )−1，大于 0.18 (10 yr)−1 的多模型集合平均值。本研究从温带海面温度（SST）方面探讨了模式差异背后的潜在因素。与 SAM 相关的温带海温异常在中高纬度之间表现出类似偶极子的结构，称为南大洋偶极子 (SOD)。在 AMIP 模拟中发现了类似 SOD 的 SST 异常在影响 SAM 中的作用。模拟 SAM 趋势的模型性能与反映 SOD-SAM 关系的模型技能有关。SOD 和 SAM 之间具有更强联系的模型倾向于模拟更强的 SAM 趋势。AMIP 运行中解释的方差约为 40%。这些结果表明 SOD-SAM 关系的改进模拟可能有助于重现 SAM 的长期变化。