Investigating the Roles of External Forcing and Ocean Circulation on the Atlantic Multidecadal SST Variability in a Large Ensemble Climate Model Hierarchy
Investigating the Roles of External Forcing and Ocean Circulation on the Atlantic Multidecadal SST Variability in a Large Ensemble Climate Model Hierarchy
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DOI：
10.1175/jcli-d-20-0167.1
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发表时间：
2021-03
影响因子：
4.9
通讯作者：
L. Murphy;J. Klavans;A. Clement;M. Cane
中科院分区：
文献类型：
--
作者：
L. Murphy;J. Klavans;A. Clement;M. Cane
本文试图加深我们对大西洋多年代际变率（AMV）成因的理解。根据文献，我们将 AMV 定义为北大西洋盆地的海温平均值，经过线性去趋势和低通滤波。关于 AMV 的驱动因素一直存在争论，其中包括海洋或大气（或两者）产生的内部变化以及外部辐射强迫。我们使用来自完全耦合版本的 CESM 的 41 成员系综和耦合到板状海洋的 CESM 大气的 10 成员系综来测试这些因素在解释 AMV 的时间历史、方差和空间模式中的作用。大型集合使我们能够分离出外部强迫与内部变化的作用，而模型差异使我们能够分离出耦合海洋环流的作用。无论有或没有耦合海洋环流，外强迫解释了观测到的 AMV 时间序列一半以上的方差，表明其在模拟 20 世纪 AMV 阶段中的重要作用。在此模型中，海洋过程的净效应是减少 AMV 的方差。动力海洋耦合也会降低模型模拟AMV特征空间格局的能力，但强迫对格局影响不大。历史强迫改善了 AMV 模拟的时间历史和方差，而更真实的海洋表示将方差降低到观测值以下，并降低了与观测值的相关性。
This paper attempts to enhance our understanding of the causes of Atlantic Multidecadal Variability, the AMV. Following the literature, we define the AMV as the SST averaged over the North Atlantic basin, linearly detrended and low-pass filtered. There is an ongoing debate about the drivers of the AMV, which include internal variability generated from the ocean or atmosphere (or both), and external radiative forcing. We test the role of these factors in explaining the time history, variance, and spatial pattern of the AMV using a 41-member ensemble from a fully coupled version of CESM and a 10-member ensemble of the CESM atmosphere coupled to a slab ocean. The large ensemble allows us to isolate the role of external forcing versus internal variability, and the model differences allow us to isolate the role of coupled ocean circulation. Both with and without coupled ocean circulation, external forcing explains more than half of the variance of the observed AMV time series, indicating its important role in simulating the 20th century AMV phases. In this model the net effect of ocean processes is to reduce the variance of the AMV. Dynamical ocean coupling also reduces the ability of the model to simulate the characteristic spatial pattern of the AMV, but forcing has little impact on the pattern. Historical forcing improves the time history and variance of the AMV simulation, whilst the more realistic ocean representation reduces the variance below that observed and lowers the correlation with observations.