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墨西哥湾流有多稳定?会突然停止吗?

我不是完全清楚西方的强化手段,但它看起来像一个非常强大的(组合)的力量,想必不会有可能的时间尺度变化对年(甚至是几十年,几百年)。

但我记得阅读前一段时间,全球变暖已经是已知的导致的数量显著增加新鲜的(相对于盐)水系统引入欧洲。我假设的“url”融化的冰川和雪/冰在以前冻土地区,但就我所知可能有更简单的(潜在)大量增加带来的降水在欧洲西北部。

我坦率地承认我不知道的相对重要性暖和/冷咸/淡水在墨西哥湾流的热力学系统,这可能是相关的。但是我真正想知道的是……

我们充分理解墨西哥湾流将回答在我的标题提出的问题吗?

回答

在某些能力,微分加热负责海洋的对流运动由于活跃的力量。然而,它可能表明,净(垂直集成)水平运输在大多数海洋完全是因为水面上的风应力的作用(斯维德鲁普,1947)。换句话说,洋流的模式主要是风应力的直接模式的镜子。当前的主要原因是加强西部边界是由于\β影响美元,或与纬度科里奥利的加强。这种效应会导致海洋表面的斜率更陡因为赤道东风西边比中纬度西风带,因此表面水堆积在西部边界。由于潜在的涡度守恒陡峭斜坡的结果在更快地转流,一边旋转(即西方强化)。西集约化的另一个原因是密度梯度,即纬向密度的梯度的迹象。例如,如果密度在极地突然变得比密度在赤道地区,西部边界电流会明显较弱。另一个论点解释西方强化的现象通过积累的能量由于向西传播行星罗斯比波。如果我们假设墨西哥湾流的流速是U \ sim 1 m / s美元平均(其最大可能的两倍)的动量单位体积流体包裹将美元\ρU \ sim 1000公斤美元$ ^ {2}$ s $ ^ {1} $。 Typical estimates suggest the total mass transport across a cross section of the Gulf stream is on the order of $90 \cdot 10^6$ m$^{3}$ s$^{-1}$ of water. By comparison, the momentum of a fluid element in the jet stream in the atmosphere is one order of magnitude smaller than that in the Gulf stream, despite the fact that the wind speed is one hundred times larger than the water current speed. Assume the gulf stream has a total volume $V = L \cdot W \cdot D$, where the length $L = 2500$ km, the width $W = 75$ km and the depth $D = 800$ m then, as a crude approximation, we can estimate the total force $F$ that must act on the fluid over (lets say) $2$ years to cause a sufficient change in the bulk fluid momentum $m \Delta v = \rho V \Delta v$ so that the Gulf Stream comes to a stop. From Newton's Second Law and plugging in some typical values: $F = m \frac{\Delta v}{\Delta t} = 2.5 \cdot 10^9$N Suppose the force is applied through a surface wind and suppose its action extends all the way to the bottom of the current. Then one would require a wind stress $\tau = 0.01$ Pa acting for at least two years, of course that number would need to be higher since in reality the wind stress accelerates the top layer of the water column, and its effect weakens with depth. Note that typical oceanic values of wind stresses are about $0.1$ Pa. This indicates that, purely from physical principles, stopping the Gulf stream within two years is realistic. However, it is not possible without a complete reversal of well established wind patterns combined with a drastic reduction in the density near the poles compared to near the equator. The latter is why some models predict future slowdown of the Gulf Stream, as the anthropogenic heating of the earth causes the melting of polar ice, the ocean water becomes fresher and less dense. Fortunately, as @naught101 pointed out, changes of that magnitude are unlikely to take place in the near future. ---------- [Sverdrup, Harald Ulrich. "Wind-driven currents in a baroclinic ocean; with application to the equatorial currents of the eastern Pacific." Proceedings of the National Academy of Sciences of the United States of America 33.11 (1947): 318.][1] Pedlosky, Joseph. "Geophysical fluid dynamics." New York and Berlin, Springer-Verlag, 1982. 636 p. 1 (1982). [1]: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1079064/pdf/pnas01704-0018.pdf

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