On warm bias and mesoscale dynamics setting the Southern Ocean large-scale circulation mean state

IF 3.1 3区 地球科学 Q2 METEOROLOGY & ATMOSPHERIC SCIENCES Ocean Modelling Pub Date : 2024-08-31 DOI:10.1016/j.ocemod.2024.102426
Mathias Zeller, Torge Martin
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Abstract

A realistic representation of the Southern Ocean (SO) in climate models is critical for reliable global climate projections. However, many models are still facing severe biases in this region. Using a fully coupled global climate model at non-eddying (1/2) and strongly eddying (1/10) grid resolution in the SO, we investigate the effect of a 0.5 °C, 1.0 °C and 1.6 °C warmer than observed SO on i) the spin-up behaviour of the high-resolution simulation, and ii) the representation of main dynamical features, i.e., the Antarctic circumpolar current (ACC), the subpolar gyres, the overturning circulation and the Agulhas regime in a quasi-equilibrium state. The adjustment of SO dynamics and hydrography critically depends on the initial state and grid resolution. When initialised with an observed ocean state, only the non-eddying configuration quickly builds up a strong warm bias in the SO. The high-resolution configuration initialised with the biased non-eddying model state results in immense spurious open ocean deep convection, as the biased ocean state is not stable at eddying resolution, and thus causes an undesirable imprint on global circulation. The SO heat content also affects the large-scale dynamics in both low- and high-resolution configurations. A warmer SO is associated with a stronger Agulhas current and a temperature-driven reduction of the meridional density gradient at 45S to 65S and thus a weaker ACC. The eddying simulations have stronger subpolar gyres under warmer conditions while the response in the non-eddying simulations is inconsistent. In general, SO dynamics are more realistically represented in a mesoscale-resolving model at the cost of requiring an own spin-up.

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关于南大洋大尺度环流平均状态的暖偏差和中尺度动力学设定
在气候模式中真实再现南大洋(SO)对于可靠的全球气候预测至关重要。然而,许多模式在这一区域仍面临严重偏差。利用南大洋无漩涡(1/2∘)和强漩涡(1/10∘)网格分辨率的全耦合全球气候模式,我们研究了比观测到的南大洋温度高 0.5 ℃、1.0 ℃ 和 1.6 ℃ 对以下方面的影响:i) 高分辨率模拟的自旋行为;ii) 主要动力学特征的代表性,即南极环极洋流(ACC)、副极地涡旋、倾覆环流和阿古哈斯系统处于准平衡状态。SO 动力学和水文地理学的调整主要取决于初始状态和网格分辨率。当以观测到的海洋状态进行初始化时,只有非漩涡配置能迅速在 SO 中建立起强烈的暖偏差。用有偏差的非漩涡模式状态初始化的高分辨率配置会产生大量虚假的开阔洋深层对流,因为有偏差的海洋状态在漩涡分辨率下并不稳定,因此会对全球环流造成不良影响。SO 热量含量也会影响低分辨率和高分辨率配置下的大尺度动力学。较暖的 SO 与较强的阿古哈斯洋流和温度驱动的 45∘S 至 65∘S 经向密度梯度的减小有关,从而减弱了 ACC。在较暖条件下,漩涡模拟的副极地涡旋更强,而非漩涡模拟的反应则不一致。一般来说,中尺度分辨率模式能更真实地反映 SO 动力,但代价是需要自旋。
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来源期刊
Ocean Modelling
Ocean Modelling 地学-海洋学
CiteScore
5.50
自引率
9.40%
发文量
86
审稿时长
19.6 weeks
期刊介绍: The main objective of Ocean Modelling is to provide rapid communication between those interested in ocean modelling, whether through direct observation, or through analytical, numerical or laboratory models, and including interactions between physical and biogeochemical or biological phenomena. Because of the intimate links between ocean and atmosphere, involvement of scientists interested in influences of either medium on the other is welcome. The journal has a wide scope and includes ocean-atmosphere interaction in various forms as well as pure ocean results. In addition to primary peer-reviewed papers, the journal provides review papers, preliminary communications, and discussions.
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