On the Emergence of the Atlantic Multidecadal SST Signal: A Key Role of the Mixed Layer Depth Variability Driven by North Atlantic Oscillation
On the Emergence of the Atlantic Multidecadal SST Signal: A Key Role of the Mixed Layer Depth Variability Driven by North Atlantic Oscillation
复制标题
大西洋多年代海温信号的出现：北大西洋涛动驱动的混合层深度变化的关键作用
DOI：
10.1175/jcli-d-19-0283.1
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发表时间：
2020
影响因子：
4.9
通讯作者：
Nonaka Masami
中科院分区：
文献类型：
--
作者：
Yamamoto Ayako;Tatebe Hiroaki;Nonaka Masami
尽管其广泛的潜在影响，大西洋多年振荡/变率（AMO/AMV）的确切原因远未解决。AMO海表温度（SST）型的出现通常被归因于海洋热量输送，最近的研究表明，大气随机强迫是足够的。在这项研究中，我们解决了这个难题，分区的几十年SST趋势的一部分所造成的表面热通量和海洋动力学，使用前工业控制模拟的一个国家的最先进的耦合气候模式。在该模型中，水平海洋热平流主要作用于温暖的副极地SST在以前的研究中，但是，当垂直分量也被认为是，海洋动力学的整体作用，以冷却该地区。或者，热通量项是主要负责副极地北大西洋SST变暖，虽然相关的表面热通量异常是向上观察。热通量项的进一步分解表明，正是混合层深度（MLD）的加深使海洋对冷却的敏感性降低，从而通过增加海洋热容量导致相对变暖。MLD变异性在AMO特征中的作用在以前的研究中尚未得到解决。MLD的变化主要是由墨西哥湾流的异常盐度输送调制的几十年北大西洋涛动，湍流通量起次要作用。因此，根据我们如何解释MLD的变化，我们的结果支持两个先前提出的框架，但稍微修改以前的概念。
Despite its wide-ranging potential impacts, the exact cause of the Atlantic multidecadal oscillation/variability (AMO/AMV) is far from settled. While the emergence of the AMO sea surface temperature (SST) pattern has been conventionally attributed to the ocean heat transport, a recent study showed that the atmospheric stochastic forcing is sufficient. In this study, we resolve this conundrum by partitioning the multidecadal SST tendency into a part caused by surface heat fluxes and another by ocean dynamics, using a preindustrial control simulation of a state-of-the-art coupled climate model. In the model, horizontal ocean heat advection primarily acts to warm the subpolar SST as in previous studies; however, when the vertical component is also considered, the ocean dynamics overall acts to cool the region. Alternatively, the heat flux term is primarily responsible for the subpolar North Atlantic SST warming, although the associated surface heat flux anomalies are upward as observed. Further decomposition of the heat flux term reveals that it is the mixed layer depth (MLD) deepening that makes the ocean less susceptible for cooling, thus leading to relative warming by increasing the ocean heat capacity. This role of the MLD variability in the AMO signature had not been addressed in previous studies. The MLD variability is primarily induced by the anomalous salinity transport by the Gulf Stream modulated by the multidecadal North Atlantic Oscillation, with turbulent fluxes playing a secondary role. Thus, depending on how we interpret the MLD variability, our results support the two previously suggested frameworks, yet slightly modifying the previous notions.