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Mechanisms of interdecadal climate variability and the role of ocean-atmosphere coupling

机译：年代际气候变化的机制和海洋-大气耦合的作用

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Climate variability and mid-latitude mechanisms of ocean-atmosphere interactions are investigated with coupled and uncoupled integrations of a three-dimensional ocean-atmosphere-land-ice climate model of intermediate complexity. We focus on the decadal and interdecadal variability of the system and give a statistical and dynamical description of its oceanic and atmospheric signatures. In our coupled control integration, an oceanic oscillation of a period of around 20 years is found to be associated with variability of the meridional overturning circulation and is manifested by surface anomalies of temperature and salinity. On such timescales the oceanic oscillation is able to imprint itself on the atmosphere, which then covaries with the ocean at the oscillation period. The essentially slaved atmospheric pattern helps maintain the oceanic oscillation by providing large-scale anomalous heat fluxes, so catalyzing the oscillation. That is to say, because the atmosphere covaries with the ocean the damping felt by the ocean is less than what would be felt with a fixed atmosphere, so broadening the parameter regime over which such variability occurs. In addition to the presence of an atmosphere, the period and amplitude of the oscillation are found to be influenced both by the oceanic vertical diffusivity k_v, by geometrical factors, and by the presence of stochastic heat fluxes. In general, oscillations occur most readily for large values of k_v, when the mean state of the ocean is characterized by a strong meridional overturning circulation. If k_v is sufficiently strong, the ocean will oscillate even in the absence of arndynamical atmosphere. However, for more realistic values of k_v, the presence of an interacting atmosphere is required for significant oscillations. If the ocean is forced by imposed stochastic heat fluxes, instead of a fully interacting atmosphere, then decadal-scale oscillations can be produced suggestive of a damped oscillator. However, the parameter range over which oscillations occur is smaller than when the ocean is coupled to full atmosphere. More genetically, the ability of comprehensive coupled ocean-atmosphere models to produce multi-decadal variability, realistic or otherwise, will depend on the oceanic mean state, and so on the diapycnal diffusivity of the modelled ocean, as well as on the ability of the atmosphere to reduce the damping felt by the ocean and so on the atmosphere's ability to respond to persistent sea-surface temperature anomalies.
机译：利用中等复杂性的三维海洋-大气-陆冰气候模型的耦合和非耦合积分研究了海洋-大气相互作用的气候变异性和中纬度机制。我们关注系统的年代际和年代际变化，并给出其海洋和大气特征的统计和动态描述。在我们的耦合控制集成中，发现大约20年的海洋振荡与子午翻转循环的变化有关，并表现为温度和盐度的表面异常。在这样的时间尺度上，海洋振荡能够将自身烙印在大气上，然后在振荡周期与海洋协变。本质上是被动的大气模式通过提供大规模的异常热通量来帮助维持海洋振荡，从而促进了振荡。就是说，由于大气随海洋变化，海洋所感受到的阻尼小于固定大气所感受到的阻尼，因此拓宽了发生这种变化的参数范围。除了存在大气之外，还发现振荡的周期和幅度受海洋垂直扩散率k_v，几何因素以及随机热通量的影响。通常，当海洋的平均状态具有强烈的子午翻转环流时，对于较大的k_v值，振荡最容易发生。如果k_v足够强，那么即使在没有动力动力学大气的情况下，海洋也会振荡。但是，对于更现实的k_v值，需要存在相互作用的气氛才能产生明显的振荡。如果海洋是由施加的随机热通量而不是完全相互作用的大气所强迫，则可能会产生年代际规模的振荡，这表明存在衰减的振荡器。但是，发生振荡的参数范围比将海洋耦合到完整大气时要小。从基因上讲，全面的海洋-大气耦合模型产生多年代际变化（无论是否现实）的能力将取决于海洋平均状态，以及建模海洋的对流扩散率，以及海洋的能力。大气层以减少海洋的阻尼感，等等，大气层对持续的海面温度异常做出响应的能力。

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