Occurrence and characteristics of mesoscale eddies in the tropical northeast Atlantic Ocean
Occurrence and characteristics of mesoscale eddies in the tropical northeast Atlantic Ocean
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DOI：
10.5194/os-12-663-2016
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发表时间：
2015-04
期刊：
影响因子：
3.2
通讯作者：
F. Schütte;P. Brandt;J. Karstensen
中科院分区：
文献类型：
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作者：
F. Schütte;P. Brandt;J. Karstensen
摘要：对热带东北大西洋（北纬12 - 22°、西经15 - 26°之间）的中尺度相干特征（此处称为涡旋）进行了研究和描述。利用19年的卫星海平面异常（SLA）数据对涡旋的表面特征进行了调查。应用了两种自动检测方法，一种是基于涡旋核心周围闭合流线的几何方法，另一种是基于涡度和应变关系的大久保 - 魏斯（Okubo - Weis）方法。两种方法得出的结果相似。从已识别涡旋核心周围所有瞬时值的合成数据中，获得了海平面异常（SLA）、海表温度（SST）和海表盐度（SSS）异常的平均涡旋表面特征。反气旋/气旋通过海平面异常的升高/降低以及其核心处海表温度和海表盐度的升高/降低来识别。然而，所有反气旋旋转涡旋中约20%的涡旋核心处海表温度和海表盐度反而降低。这类涡旋被归类为反气旋模态水涡旋（ACMEs）。每年识别出约146 ± 4个涡旋，其最小寿命为7天（气旋占52%，反气旋占39%，反气旋模态水涡旋占9%），平均半径约为56 ± 12 km。基于在涡旋内部获取的同期现场温度和盐度剖面（来自阿尔戈浮标、船载和系泊数据），确定了三种涡旋类型独特的平均垂直结构。大多数涡旋优先在北半球夏季于西非海岸三个不同的海岸岬角区域生成，并携带由毛里塔尼亚沿岸流系统内的北向流所供应的南大西洋中央水。涡旋向西传播（平均约为3.00 ± 2.15 km/d）局限于特定的纬向走廊，其经向偏转较小且取决于涡旋类型（反气旋 - 向赤道方向，气旋 - 向极地方向，反气旋模态水涡旋 - 无偏转）。计算了从沿海地区流出并穿过佛得角锋区（该锋区将阴影区与通风的副热带环流分开）的热量和盐通量。
Abstract. Coherent mesoscale features (referred to here as eddies) in the tropical northeastern Atlantic Ocean (between 12–22° N and 15–26° W) are examined and characterized. The eddies' surface signatures are investigated using 19 years of satellite-derived sea level anomaly (SLA) data. Two automated detection methods are applied, the geometrical method based on closed streamlines around eddy cores, and the Okubo–Weis method based on the relation between vorticity and strain. Both methods give similar results. Mean eddy surface signatures of SLA, sea surface temperature (SST) and sea surface salinity (SSS) anomalies are obtained from composites of all snapshots around identified eddy cores. Anticyclones/cyclones are identified by an elevation/depression of SLA and enhanced/reduced SST and SSS in their cores. However, about 20 % of all anticyclonically rotating eddies show reduced SST and reduced SSS instead. These kind of eddies are classified as anticyclonic mode-water eddies (ACMEs). About 146 ± 4 eddies per year with a minimum lifetime of 7 days are identified (52 % cyclones, 39 % anticyclones, 9 % ACMEs) with rather similar mean radii of about 56 ± 12 km. Based on concurrent in situ temperature and salinity profiles (from Argo float, shipboard, and mooring data) taken inside of eddies, distinct mean vertical structures of the three eddy types are determined. Most eddies are generated preferentially in boreal summer and along the West African coast at three distinct coastal headland regions and carry South Atlantic Central Water supplied by the northward flow within the Mauretanian coastal current system. Westward eddy propagation (on average about 3.00 ± 2.15 km d−1) is confined to distinct zonal corridors with a small meridional deflection dependent on the eddy type (anticyclones – equatorward, cyclones – poleward, ACMEs – no deflection). Heat and salt fluxes out of the coastal region and across the Cape Verde Frontal Zone, which separates the shadow zone from the ventilated subtropical gyre, are calculated.