Surging of Global Surface Temperature due to Decadal Legacy of Ocean Heat Uptake
Surging of Global Surface Temperature due to Decadal Legacy of Ocean Heat Uptake
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DOI：
10.1175/jcli-d-19-0874.1
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发表时间：
2020-09
影响因子：
4.9
通讯作者：
B. Sinha;F. Sévellec;J. Robson;G. Nurser
中科院分区：
文献类型：
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作者：
B. Sinha;F. Sévellec;J. Robson;G. Nurser
自1850年以来，全球表面变暖包括一系列放缓(间歇)和随后的激增。了解一种解释这种现象如何发生的机制将有助于开发和测试年际至年代际气候预报。在本文中，全球气候模式被迫采用与间歇期[具有负的年代际太平洋振荡(IPO)和其他间歇期典型的地表特征]相对应的海洋状态，方法是人为地增加背景扩散率10年，然后将其恢复到其正常值并允许模式自由演化。这导致该模型形成了一种超过均衡的十年激增(导致了积极的IPO状态)，留下了几十年来修改后的、更温暖的气候。水-质转换诊断表明，热带太平洋的热收支是大的对号项之间的平衡：由海-气热通量引起的表面加热/冷却被垂直混合和海洋热输送散度所平衡。在人工间歇期间，多余的热量被困在温跃层的正上方，并有一个微弱的垂直温度梯度(由于高度的人工背景混合)。当间歇期终止时，通过使背景扩散率恢复到正常，温度梯度增强到间歇期前的值，因此混合(扩散率×热梯度)保持大致恒定。然而，由于温跃层上方的底层保持异常温暖，这意味着滞留热量上方的整个水柱变暖，这导致海浪激增，随后地表温度长期上升。
Global surface warming since 1850 has consisted of a series of slowdowns (hiatus) followed by surges. Knowledge of a mechanism to explain how this occurs would aid development and testing of interannual to decadal climate forecasts. In this paper a global climate model is forced to adopt an ocean state corresponding to a hiatus [with negative interdecadal Pacific oscillation (IPO) and other surface features typical of a hiatus] by artificially increasing the background diffusivity for a decade before restoring it to its normal value and allowing the model to evolve freely. This causes the model to develop a decadal surge that overshoots equilibrium (resulting in a positive IPO state), leaving behind a modified, warmer climate for decades. Water-mass transformation diagnostics indicate that the heat budget of the tropical Pacific Ocean is a balance between large opposite-signed terms: surface heating/cooling resulting from air–sea heat flux is balanced by vertical mixing and ocean heat transport divergence. During the artificial hiatus, excess heat becomes trapped just above the thermocline and there is a weak vertical thermal gradient (due to the high artificial background mixing). When the hiatus is terminated, by returning the background diffusivity to normal, the thermal gradient strengthens to prehiatus values so that the mixing (diffusivity × thermal gradient) remains roughly constant. However, since the base layer just above the thermocline remains anomalously warm, this implies a warming of the entire water column above the trapped heat, which results in a surge followed by a prolonged period of elevated surface temperatures.