On mean and seasonal currents and transports at the western boundary of the equatorial Atlantic
On mean and seasonal currents and transports at the western boundary of the equatorial Atlantic
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赤道大西洋西边界的平均和季节性洋流及输送
DOI：
10.1029/93jc01287
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发表时间：
1993
影响因子：
--
通讯作者：
U. Send
中科院分区：
文献类型：
--
作者：
F. Schott;J. Fischer;J. Reppin;U. Send
在大西洋赤道西端，沿着44 ° W，连续两年部署三个系泊站的海流测量被用来确定上层几百米的暖水向西北流动和北大西洋深水（NADW）向东南逆流。从三个声学多普勒海流剖面仪（ADCPs）的测量向上看，从300米的表面允许计算的时间序列的上层运输超过1年。通过阵列的平均输送量为23.8 Sv，年周期仅为± 3 Sv，最大值出现在6 - 8月，最小值出现在北方春季。根据系泊数据和Pegasus船载数据以及降低的ADCP剖面，估计300 - 600 m范围内的额外平均西北输送为6.7 Sv。在1 400 - 3 100米深度范围内，沿着大陆坡发现了一个最大年平均东南向速度为30厘米·秒-1的海流岩心，根据岩心系泊和大陆坡之间使用的外推法，估计上部NADW的迁移量为14.2 - 17.3西沃特。这种运输高于离赤道的估计，并建议近赤道的再循环在NADW上的水平，在协议中发现约140公里的离岸西北平均流。在3100米以下和1.8 ° C等温线以上，只有在海盆靠近1.5 ° N的平坦部分发现一个小的低NADW流核心，速度为10 - 15 cm s − 1，与大陆坡明显分开，被一个平均速度接近零的区域隔开。小电流核心的估计输运量约为4.5西沃特，这大大低于低NADW近赤道输运的其他估计值，表明低NADW的大部分可能穿过塞阿拉海隆以北的西经44 °。季内变率很大，尽管比西部边界附近8 ° N观测到的要小。当它在近地表记录中占主导地位时，它出现在大约1个月的周期内，并与所有海洋赤道区的早期观测相对应;当它在NADW一级占主导地位时，它出现在大约2个月的周期内，并可能沿着边界从北部沿着输入，或沿着赤道从东部沿着输入。高分辨率数值模型结果表明，在每秒几厘米幅度的深海海流中存在一个年周期，但由于短期变化量很大，既不能证明也不能证明这一点。
Current measurements from two consecutive yearlong deployments of three moored stations at the western end of the equator in the Atlantic, along 44°W, are used to determine the northwestward flow of warm water in the upper several 100 m and of the southeastward counterflow of North Atlantic Deep Water (NADW). Measurements from three acoustic Doppler current profilers (ADCPs) looking upward from 300 m toward the surface allowed calculation of a time series of upper layer transports over 1 year. Mean transport through the array for the upper 300 m is 23.8 Sv with an annual cycle of only ±3 Sv that has its maximum in June-August and minimum in northern spring. Estimated additional mean northwestward transport in the range 300–600 m is 6.7 Sv, based on moored data and shipboard Pegasus and lowered ADCP profiling. In the depth range 1400–3100 m a current core with maximum annual mean southeastward speed of 30 cm s−1 is found along the continental slope that carries an estimated upper NADW transport of 14.2–17.3 Sv, depending on the extrapolation used between the mooring in the core and the continental slope. This transport is higher than off-equatorial estimates and suggests near-equatorial recirculation at the upper NADW level, in agreement with northwestward mean flow found about 140 km offshore. Below 3100 m and above the 1.8°C isotherm, only a small core of lower NADW flow with speeds of 10–15 cm s−1 is found over the flat part of the basin near 1.5°N, clearly separated from the continental slope by a zone of near-zero mean speeds. Estimated transport of that small current core is about 4.5 Sv, which is significantly below other estimates of near-equatorial transport of lower NADW and suggests that a major fraction of lower NADW may cross the 44°W meridian north of the Ceara Rise. Intraseasonal variability is large, although smaller than observed at 8°N near the western boundary. It occurs at a period of about 1 month when it is dominant in the near-surface records and corresponds to earlier observations in the equatorial zones of all oceans and at a period of about 2 months when it is dominant at the NADW level and could be imported either from the north along the boundary or from the east along the equator. The existence of an annual cycle in the deep currents of a few centimeters per second amplitude, as suggested by high-resolution numerical model results, could neither be proven nor disproven because of the high amount of shorter-period variability.