On interannual to decadal time scales, memory in the Earth's climate system resides to a large extent in the slowly varying heat content of the ocean, which responds to fast atmospheric variability and in turn sets the frame for large‐scale atmospheric circulation patterns. This large‐scale coupled atmosphere–ocean feedback is generally well represented in today's Earth system models. This may fundamentally change when data assimilation is used to bring such models close to an observed state to initialize interannual to decadal climate predictions. Here, we review how the large‐scale coupled atmosphere–ocean feedback is preserved in common approaches to construct such initial conditions, with the focus on the initialized ocean state. In a set of decadal prediction experiments, ranging from an initialization of atmospheric variability only to full‐field nudging of both atmosphere and ocean, we evaluate the variability and predictability of the Atlantic meridional overturning circulation, of the Atlantic multidecadal variability and North Atlantic subpolar gyre sea surface temperatures. We argue that the quality of initial conditions for decadal predictions should not purely be assessed by their closeness to observations, but also by the closeness of their respective predictions to observations. This prediction quality may depend on the representation of the simulated large‐scale atmosphere–ocean feedback.

中文翻译：

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在年代际气候预测的初始化过程中保持大气-海洋的耦合反馈

在年际到十年的时间尺度上，地球气候系统中的记忆很大程度上驻留在海洋缓慢变化的热量中，这对快速的大气变化做出了响应，进而为大规模的大气环流模式设定了框架。在当今的地球系统模型中，这种大规模的大气-海洋耦合反馈通常可以很好地表示。当使用数据同化使此类模型接近观测状态以初始化年际至年代际气候预测时，这可能会发生根本变化。在这里，我们回顾了在构造此类初始条件的常用方法中如何保留大规模的大气-海洋反馈，重点是初始化的海洋状态。在一组年代际预测实验中，从仅对大气变化的初始化到对大气和海洋的全场探测，我们评估了大西洋子午翻转环流，大西洋多年代际变化和北大西洋次极环流海面温度的变化和可预测性。我们认为，年代际预测的初始条件的质量不应该仅通过其与观测值的接近度来评估，还应该通过其各自的预测与观测值的接近度来评估。这种预测质量可能取决于模拟的大规模大气-海洋反馈的表示形式。大西洋多年代际变化和北大西洋次极环流海面温度的变化。我们认为，年代际预测的初始条件的质量不应该仅通过其与观测值的接近度来评估，还应该通过其各自的预测与观测值的接近度来评估。这种预测质量可能取决于模拟的大规模大气-海洋反馈的表示形式。大西洋多年代际变化和北大西洋次极环流海面温度的变化。我们认为，年代际预测的初始条件的质量不应该仅通过其与观测值的接近度来评估，还应该通过其各自的预测与观测值的接近度来评估。这种预测质量可能取决于模拟的大规模大气-海洋反馈的表示形式。