Observations of atmosphere-ocean coupling in the North Atlantic
Observations of atmosphere-ocean coupling in the North Atlantic
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DOI：
10.1002/qj.49712757603
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发表时间：
2001-07-01
影响因子：
8.9
通讯作者：
Marshall, J
中科院分区：
文献类型：
--
作者：
Czaja, A;Marshall, J
介绍了一个海表温度（SST）变率指数，即Δ T，它可以用来衡量冬末分离的墨西哥湾流之间SST的差异。通过分析SST和海平面气压（SLP）的长期观测记录，它表明，DeltaT表现出衰减振荡的年代际周期，并与偶极SLP异常的强度，让人想起北大西洋涛动（NAO）的协变。在频域分析显示，在10-20年的DeltaT宽带的“峰值”，与较长的时间尺度上的功率持续下降。在SLP偶极子的北方部分（格陵兰-冰岛低区）发现了类似的光谱特征，但在其南部部分（副热带高压区）没有发现，其功率在长时间尺度上增加。DeltaT指数在长时间尺度（> 25年）上的功率下降是由一个包括风驱动的海洋环流的模式捕获的，主要是后者对NAO强迫的被动响应。海洋的纬向翻转环流的变化也可以发挥作用，在调制DeltaT的年代际时间尺度。如果在NAO模式上引入一个小的DeltaT反馈，简单的模型也可以再现格陵兰-冰岛地区的射电异常中看到的光谱结构。
An index of sea surface temperature (SST) variability, DeltaT, is introduced that measures the difference in SST across the separated Gulf Stream in late winter. By analysing a long observational record of SST and sea-level pressure (SLP), it is shown that DeltaT exhibits damped oscillations of decadal period, and covaries with the strength of a dipolar SLP anomaly reminiscent of the North Atlantic Oscillation (NAO). Analysis in the frequency domain shows a broad-band 'peak' at 10-20 years in DeltaT, with a continuous decrease of power on longer time-scales. Similar spectral signatures are found in the northern part of the SLP dipole (the Greenland-Icelandic Low region) but not in its southern part (the subtropical High region), whose power increases on long time-scales.The observations are interpreted in the framework of a delayed-oscillator model in which the ocean circulation introduces the delay, and modulates DeltaT on decadal time-scales. The decrease of power seen on long time-scales (> 25 years) in the DeltaT index is captured by a model including wind-driven ocean circulation, and arises primarily as a passive response of the latter to the NAO forcing. Variability of the ocean's meridional overturning circulation could also play a role in modulating DeltaT on decadal time-scales. If a small feedback of DeltaT on the NAO pattern is introduced, the simple model can also reproduce the spectral structures seen in the SUP anomaly in the Greenland-Iceland region.