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Variability of Shallow and Deep Western Boundary Currents off the Bahamas during 2004–05: Results from the 26°N RAPID–MOC Array

机译:2004-05年巴哈马以外的浅西部边界流和深西部边界流的变化:26°N RAPID-MOC阵列的结果

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摘要

Data from an array of six moorings deployed east of Abaco, Bahamas, along 26.5°N during March 2004–May 2005 are analyzed. These moorings formed the western boundary array of a transbasin observing system designed to continuously monitor the meridional overturning circulation and meridional heat flux in the subtropical North Atlantic, under the framework of the joint U.K.–U.S. Rapid Climate Change (RAPID)–Meridional Overturning Circulation (MOC) Program. Important features of the western boundary circulation include the southward-flowing deep western boundary current (DWBC) below 1000 m and the northward-flowing “Antilles” Current in the upper 1000 m. Transports in the western boundary layer are estimated from direct current meter observations and from dynamic height moorings that measure the spatially integrated geostrophic flow between moorings. The results of these methods are combined to estimate the time-varying transports in the upper and deep ocean over the width of the western boundary layer to a distance of 500 km offshore of the Bahamas escarpment. The net southward transport of the DWBC across this region, inclusive of northward deep recirculation, is −26.5 Sv (Sv ≡ 106 m3 s−1), which is divided nearly equally between upper (−13.9 Sv) and lower (−12.6 Sv) North Atlantic Deep Water (NADW). In the top 1000 m, 6.0 Sv flows northward in a thermocline-intensified jet near the western boundary. These transports are found to agree well with historical current meter data in the region collected between 1986 and 1997. Variability in both shallow and deep components of the circulation is large, with transports above 1000 m varying between −15 and +25 Sv and deep transports varying between −60 and +3 Sv. Much of this transport variability, associated with barotropic fluctuations, occurs on relatively short time scales of several days to a few weeks. Upon removal of the barotropic fluctuations, slower baroclinic transport variations are revealed, including a temporary stoppage of the lower NADW transport in the DWBC during November 2004.
机译:分析了2004年3月至2005年5月沿巴哈马州阿巴科以东26.5°分布的六个系泊设备的数据。这些系泊形成了跨流域观测系统的西边界阵列,该跨流域观测系统旨在在联合王国的框架下,连续监测亚热带北大西洋的子午倾覆环流和子午热通量。快速气候变化(RAPID)–经向翻转循环(MOC)程序。西部边界环流的重要特征包括在1000 m以下向南流动的深西边界流(DWBC)和在1000 m以上向北流动的“安的列斯”流。西部边界层的运输量是根据直流电表的观测值和动态高度系泊设备估算得出的,该系泊设备测量了系泊设备之间空间整合的地转流。结合这些方法的结果,可以估算出在西边界层宽度上至巴哈马悬崖近海500公里处的上层和深层海洋中随时间变化的运移。 DWBC横跨该区域的净南移,包括向北的深层回流,为-26.5 Sv(Sv≡106 m3 s-1),几乎平均地分为上(-13.9 Sv)和下(-12.6 Sv)北大西洋深水区(NADW)。在最上面的1000 m中,6.0 Sv在西边界附近的热跃层增强射流中向北流动。发现这些传输与1986年至1997年间收集的该区域的历史电流表数据非常吻合。在浅层和深层循环中的变化都很大,1000 m以上的传输在-15和+25 Sv之间变化,而深层传输在−60和+3 Sv之间变化。与正压波动相关的大部分运输变异性发生在几天至几周的相对较短的时间尺度上。消除了正压波动后,斜压运移速度变慢了,包括2004年11月DWBC中较低NADW运移的暂时停止。

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