Decadal variability in the Kuroshio-Oyashio Extension simulated in an eddy-resolving OGCM
Decadal variability in the Kuroshio-Oyashio Extension simulated in an eddy-resolving OGCM
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DOI：
10.1175/jcli3793.1
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发表时间：
2006-05-15
影响因子：
4.9
通讯作者：
Sasaki, Hideharu
中科院分区：
文献类型：
--
作者：
Nonaka, Masami;Nakamura, Hisashi;Sasaki, Hideharu
通过对涡解准全球海洋环流模型的后报积分分析，研究了黑潮-亲潮延伸区的年代际变化，特别是亚北极（亲潮）和黑潮延伸（KE）锋面的变化。 KE锋面很深，并伴随着急剧的海面高度（SSH）梯度和适度的海面温度（SST）梯度。相比之下，亚北极锋面较浅，被认为是海表温度梯度较紧的区域，而海表温度却不是这样。随着从1970年左右的温暖时期到1980年代中期的凉爽时期的十年尺度变化，模型中的这些锋面如观察到的那样向南迁移，相关的明显变冷主要局限于这些锋面区域。反映了锋面独特的垂直结构，混合层冷却沿亚北极锋面最强，而地下冷却和相关盐度变化沿KE锋面最明显。伴随着它们的南移，两条战线经历了十年尺度的强化。与释放到大气中的热量减少相关，锋区的冷却既不能归因于直接的大气热强迫，也不能归因于增强的KE的平流效应，而强烈的亲潮的平流效应可以促进亚北极锋区的冷却。事实上，它们的时间演化并不完全一致，这表明它们的变化可能是由不同的机制控制的。 KE 锋区的年代际 SSH 变化似乎主要是由北太平洋中部异常埃克曼抽水迫使斜压罗斯贝波的传播来解释的。仅这个过程并不能完全解释亚北极锋区的相应变化，在该地区，日本海岸向东传播的海啸异常似乎叠加在罗斯贝波信号上。
Through analysis of a hindcast integration of an eddy-resolving quasi-global ocean general circulation model, decadal variability in the Kuroshio-Oyashio Extension region is investigated, with particular emphasis on that of the subarctic (Oyashio) and the Kuroshio Extension (KE) fronts. The KE front is deep and is accompanied by a sharp sea surface height (SSH) gradient with modest sea surface temperature (SST) gradient. In contrast, the subarctic front is shallow and is recognized as a zone of tight gradient in SST but not SSH.As a decadal-scale change from a warm period around 1970 to a cool period in the mid-1980s, those fronts in the model migrate southward as observed, and the associated pronounced cooling is confined mainly to those frontal zones. Reflecting the distinctive vertical structure of the fronts, the mixed layer cooling is the strongest along the subarctic front, whereas the subsurface cooling and the associated salinity changes are most pronounced along the KE front. Concomitantly with their southward migration, the two fronts have undergone decadal-scale intensification. Associated with reduced heat release into the atmosphere, the cooling in the frontal zones can be attributed neither to the direct atmospheric thermal forcing nor to the advective effect of the intensified KE, while the advective effect by the intense Oyashio can contribute to the cooling in the subarctic frontal zone.In fact, their time evolution is not found to be completely coherent, suggesting that their variability may be governed by different mechanisms. Decadal SSH variability in the KE frontal zone seems to be largely explained by propagation of baroclinic Rossby waves forced by anomalous Ekman pumping in the central North Pacific. This process alone cannot fully explain the corresponding variability in the subarctic frontal zone, where eastward propagating SSH anomalies off the Japanese coast seem to be superimposed on the Rossby wave signals.