Loop Current Variability as Trigger of Coherent Gulf Stream Transport Anomalies
Loop Current Variability as Trigger of Coherent Gulf Stream Transport Anomalies
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DOI：
10.1175/jpo-d-18-0236.1
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发表时间：
2019-08-01
影响因子：
3.5
通讯作者：
Madec, Gurvan
中科院分区：
文献类型：
--
作者：
Hirschi, Joel J. -M.;Frajka-Williams, Eleanor;Madec, Gurvan
卫星观测和高分辨率海洋模式的输出被用来调查如何在墨西哥湾的环流影响墨西哥湾流传输通过佛罗里达海峡。我们发现环流的扩张（收缩）导致通过佛罗里达海峡的输送量降低（增加）。从佛罗里达西南端到哈特拉斯角，相关的表面速度异常是相干的。一个简单的基于连续性的论点可以用来解释环流和下游墨西哥湾流运输之间的联系：随着环流在墨西哥湾的路径延长（缩短），流出墨西哥湾的流量减少（增加）。表面速度场的异常首先出现在佛罗里达西南部，并在4周内通过佛罗里达海峡传播到哈特拉斯角，进入墨西哥湾流延伸区。在观测和模型中，这种传播可以被看作是表面速度的脉冲。我们估计，通过佛罗里达海峡，环流的变化可以与几个Sverdrups（1 Sv = 10（6）m（3）s（-1））的变化联系起来。环流变化的确切时间在几周内很大程度上是不可预测的，因此它的变化可能是墨西哥湾流混乱/内在变化的主要原因。然而，环流与墨西哥湾下游水流之间的时滞意味着，如果观察到环流的延长/缩短，这将在几周内对下游水流产生一些可预测性。
Satellite observations and output from a high-resolution ocean model are used to investigate how the Loop Current in the Gulf of Mexico affects the Gulf Stream transport through the Florida Straits. We find that the expansion (contraction) of the Loop Current leads to lower (higher) transports through the Straits of Florida. The associated surface velocity anomalies are coherent from the southwestern tip of Florida to Cape Hatteras. A simple continuity-based argument can be used to explain the link between the Loop Current and the downstream Gulf Stream transport: as the Loop Current lengthens (shortens) its path in the Gulf of Mexico, the flow out of the Gulf decreases (increases). Anomalies in the surface velocity field are first seen to the southwest of Florida and within 4 weeks propagate through the Florida Straits up to Cape Hatteras and into the Gulf Stream Extension. In both the observations and the model this propagation can be seen as pulses in the surface velocities. We estimate that the Loop Current variability can be linked to a variability of several Sverdrups (1Sv = 10(6) m(3) s(-1)) through the Florida Straits. The exact timing of the Loop Current variability is largely unpredictable beyond a few weeks and its variability is therefore likely a major contributor to the chaotic/intrinsic variability of the Gulf Stream. However, the time lag between the Loop Current and the flow downstream of the Gulf of Mexico means that if a lengthening/shortening of the Loop Current is observed this introduces some predictability in the downstream flow for a few weeks.