NORTH–SOUTH SHIFTS OF THE GULF STREAM: OCEAN‐ATMOSPHERE INTERACTIONS IN THE NORTH ATLANTIC
NORTH–SOUTH SHIFTS OF THE GULF STREAM: OCEAN‐ATMOSPHERE INTERACTIONS IN THE NORTH ATLANTIC
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墨西哥湾流的南北移动：北大西洋的海洋与大气相互作用
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发表时间：
1996
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通讯作者：
A. Taylor
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作者：
A. Taylor
墨西哥湾流北壁纬度的逐年变化与不列颠群岛周围连续浮游生物记录仪观测到的浮游动物丰度变化以及温德米尔湖浮游动物丰度变化非常相似。这些联系必须反映北大西洋不断变化的天气模式。湾流位置指数是根据北壁数据通过主成分分析构建的。第一个主成分，即所使用的指数，具有全部具有相同符号的特征向量系数，并且是整个北墙的纬度的度量。然而，该分量可能代表在空间和时间上广泛的曲流的发生，而不是整个湾流的位移。该主成分已用于计算月平均海平面压力和月平均气旋路径数量的加权平均值，以显示与北墙位移相关的天气模式的变化。
北墙向北移动的同时，大西洋最北端地区（每年和秋季）气旋数量显着减少，并且在春季、夏季和秋季，大西洋中部地区北纬 40°–60°、西经 30°–50° 的气压降低（局部显着）。该地区南侧的风暴路径有一定的偏转趋势（不显着）。冬季的模式不太明显，没有显示出统计意义。不列颠群岛附近的变化通常太小，不具有统计显着性，但通常与春季和秋季风暴频率较低的情况一致。由于生物变化似乎是由春季热层化开始的变化引起的，因此它们可能是大气强迫相对较小变化的结果。大气变化没有表明墨西哥湾流位移的来源，异常风与位移相反。这可能是因为墨西哥湾流的蜿蜒并不简单地与任何单一的大气变量相关。
最清晰、最具统计意义的气象信号都在北墙下游。尽管北壁的位移是由北大西洋天气模式变化引起的，但墨西哥湾流也是从海洋到大气的强烈热量传递的区域。索耶的标准表明，该热源的扭曲可能会对北大西洋的大气环流造成明显的干扰。基于 Smagorinsky 分析模型的数值模型用于研究该局部热源的位移可能引起的纬向环流的扰动。这些预测与夏季、春季和秋季（但冬季）大西洋中部的变化一致。在模型预测的大气压力下降的区域，北壁位置与地面大气压力之间不存在正相关系数，但与偶然相比，负相关系数显着过量，并且湾流北移伴随着大气压力的显着下降。因此，北墙的位移可能会影响更东部的天气模式。该模型预测欧洲大陆架的任何变化都将是微弱的。准确描述墨西哥湾流的动力学可能是海洋-大气耦合模型的重要要求。
Year-to-year changes in the latitude of the north wall of the Gulf Stream are very similar to those seen in the abundances of zooplankton observed by the Continuous Plankton Recorder Survey around the British Isles and also to those in the abundance of zooplankton in Lake Windermere. These connections must reflect changing weather patterns across the North Atlantic. The index of Gulf Stream position was constructed from the north wall data by principal components analysis. The first principal component, the index used, has eigenvector coefficients that all have the same sign, and is a measure of the latitude of the whole of the north wall. However, the component may represent the occurrences of meanders that are extensive in space and time rather than displacements of the Gulf Stream as a whole. This principal component has been used to calculate weighted averages of monthly mean sea-level pressure and of monthly mean numbers of cyclone tracks in order to show the changes in weather patterns associated with displacements of the north wall.
Northward displacements of the north wall were accompanied by significantly reduced cyclone numbers in the northernmost regions of the Atlantic (annually and in the autumn) and, in spring, summer, and autumn, a region of reduced atmospheric pressure in the central Atlantic area 40°–60°N, 30°–50°W (locally significant). There was some tendency (not significant) for storm tracks to be deflected around the south side of this region. The pattern in winter is less clear and shows no statistical significance. Changes in the vicinity of the British Isles were generally too small to be statistically significant but were generally consistent with a lower frequency of storms in spring and autumn. As the biological changes appear to be caused by variations in the onset of thermal stratification during the spring they may be the result of relatively small changes in the atmospheric forcing. The atmospheric changes show no indications of the sources of the Gulf Stream displacements, the anomaly winds opposing the displacements. This may be because meanders of the Gulf Stream are not simply related to any single atmospheric variable.
The clearest and most statistically significant meteorological signals were all well downstream from the north wall. Although the displacements of the north wall are caused by changing weather patterns over the North Atlantic, the Gulf Stream is also a region of strong heat transfers from the ocean to the atmosphere. Sawyer's criterion indicates that distortions of this heat source could cause noticeable disturbances to the atmospheric circulation over the North Atlantic. A numerical model based on the analytical model of Smagorinsky is used to investigate the perturbations of the zonal circulation that might be caused by displacements of this local heat source. The predictions are in agreement with the changes seen in the central Atlantic during summer, spring, and autumn (but not those during winter). In the region where the model predicts atmospheric pressure reductions should occur, there are no positive correlation coefficients between the position of the north wall and the surface atmospheric pressure but a significant excess of negative correlation coefficients compared with chance, and northward shifts of the Gulf Stream were accompanied by significant reductions in atmospheric pressure. It is therefore possible that displacements of the north wall could influence weather patterns further east. The model predicts that any changes over the European continental shelf will be weak. An accurate description of the dynamics of the Gulf Stream may be an important requirement of coupled ocean–atmosphere models.