Recent research suggests the widespread existence of the signal-to-noise paradox in seasonal-to-decadal climate predictions. The essence of the paradox is that the signal-to-noise ratio in models can be unrealistically small and models may make better predictions of the observations than they predict themselves. The paradox highlights a potentially serious issue with model predictions as previous studies may underestimate the limit of predictability. The focus of this paper is two-fold: the first objective is to re-examine decadal predictability from the lens of the signal-to-noise paradox in the context of CMIP5 models. We demonstrate that decadal predictability is generally underestimated in CMIP5 models possibly due to the existence of the signal-to-noise paradox. Models underestimate decadal predictability in regions where it is likely for the paradox to exist, especially over the Tropical Atlantic Ocean and Tropical Indian Ocean and eddy-rich regions, including the Gulf Stream, Kuroshio Current, and Southern Ocean. The second objective follows from the results of the first, attempting to determine if this underestimate of decadal predictability is, at least partially, due to missing ocean mesoscale processes and features in CMIP5 models. A suite of coupled model experiments is performed with eddying and eddy-parameterized ocean component. Compared with eddy-parameterized models, the paradox is less likely to exist in eddying models, particularly over eddy-rich regions. These also happen to be regions where increased decadal predictability is identified. We hypothesize that this enhanced predictability is due to the enhanced vertical connectivity in the ocean. The presence of mesoscale ocean features and associated vertical connectivity significantly influence decadal variability, predictability, and the signal-to-noise paradox.

最近的研究表明，信噪比悖论在季节到十年的气候预测中普遍存在。悖论的实质是模型中的信噪比可能不切实际地小，并且模型对观测的预测可能比其预测本身更好。由于先前的研究可能低估了可预测性的局限性，因此悖论突出了模型预测的潜在严重问题。本文的重点有两个方面：第一个目标是在CMIP5模型的背景下，从信噪比悖论的角度重新检查年代际可预测性。我们证明，CMIP5模型中的年代可预测性通常被低估了，这可能是由于信噪比悖论的存在造成的。模型低估了可能存在悖论的地区的年代际可预测性，尤其是在热带大西洋和热带印度洋以及涡流丰富的地区，包括墨西哥湾流，黑潮洋流和南洋。第二个目标来自第一个目标，试图确定这种年代际可预测性的低估至少部分是由于缺少CMIP5模型中的海洋中尺度过程和特征。使用涡流和涡流参数化海洋成分进行了一系列耦合模型实验。与涡流参数化模型相比，在涡流模型中尤其是在涡流丰富的地区更不可能出现这种悖论。这些地区恰好是年代际可预测性提高的地区。我们假设这种增强的可预测性是由于海洋中垂直连通性的增强。中尺度海洋特征和相关的垂直连通性的存在显着影响年代际变化，可预测性以及信噪比悖论。