What causes the spread of model projections of ocean dynamic sea-level change in response to greenhouse gas forcing?
What causes the spread of model projections of ocean dynamic sea-level change in response to greenhouse gas forcing?
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DOI：
10.1007/s00382-020-05471-4
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发表时间：
2020-10-27
期刊：
影响因子：
4.6
通讯作者：
Zanna, Laure
中科院分区：
文献类型：
--
作者：
Couldrey, Matthew P.;Gregory, Jonathan M.;Zanna, Laure
不同的大气-海洋环流模型（AOGCM）的海平面以不同的方式对气候变化强迫作出反应，代表了气候变化研究中至关重要的不确定性。我们通过强制多个 AOGCM 具有规定的相同热量、动量（风）和淡水通量扰动，分离出海洋动力学在设定动态海平面 (zeta) 变化的空间模式中的作用。该方法产生的 zeta 投影扩展在大小上与温室气体强迫产生的扩展相当，表明海洋模型公式的差异才是原因，而不是表面通量变化的多样性。热通量的变化驱动了大部分 zeta 变化的全局模式，而动量和水通量的变化则导致局部受限的特征。北大西洋吸热导致温度和盐度驱动的密度变化较大，改变当地海洋运输和 zeta。 AOGCM 之间的传播很大程度上是由于其区域运输调整的差异造成的，这种调整重新分配了扰动之前海洋中已经存在的热量。北大西洋 zeta 变化的地理细节在不同模型中是不同的，但潜在的动态变化是相似的。相比之下，南大洋吸收的热量并没有强烈改变垂直相干环流。由于被动吸热和环流变化的差异，不同模型的北极 zeta 变化有所不同。只有北极受到三种海气通量变化之间非线性相互作用的强烈影响，并且这些是特定于模型的。
Sea levels of different atmosphere-ocean general circulation models (AOGCMs) respond to climate change forcing in different ways, representing a crucial uncertainty in climate change research. We isolate the role of the ocean dynamics in setting the spatial pattern of dynamic sea-level (zeta) change by forcing several AOGCMs with prescribed identical heat, momentum (wind) and freshwater flux perturbations. This method produces a zeta projection spread comparable in magnitude to the spread that results from greenhouse gas forcing, indicating that the differences in ocean model formulation are the cause, rather than diversity in surface flux change. The heat flux change drives most of the global pattern of zeta change, while the momentum and water flux changes cause locally confined features. North Atlantic heat uptake causes large temperature and salinity driven density changes, altering local ocean transport and zeta. The spread between AOGCMs here is caused largely by differences in their regional transport adjustment, which redistributes heat that was already in the ocean prior to perturbation. The geographic details of the zeta change in the North Atlantic are diverse across models, but the underlying dynamic change is similar. In contrast, the heat absorbed by the Southern Ocean does not strongly alter the vertically coherent circulation. The Arctic zeta change is dissimilar across models, owing to differences in passive heat uptake and circulation change. Only the Arctic is strongly affected by nonlinear interactions between the three air-sea flux changes, and these are model specific.