Ekman drift in homogeneous water
Ekman drift in homogeneous water
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均质水中的埃克曼漂移
DOI：
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发表时间：
1993
期刊：
影响因子：
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通讯作者：
W. Krauss
中科院分区：
文献类型：
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作者：
W. Krauss
在北海均匀冬季条件下，在海面和30米深度之间的不同层用卫星跟踪浮标进行测量，可以分析各种风况下的埃克曼海流。实验从1991年11月20日持续到1992年2月29日。在此期间的前4个星期，浮标保持靠近在一起，用于确定埃克曼应力。总流场是由海平面变化引起的正压流和埃克曼流叠加而成。经典的Ekman理论不能正确地描述观测到的海流向风向右侧的偏转及其随深度的衰减。这种偏转在海面附近为10°，在25 m深度处增加到约50°。风应力与水内部应力场之间的关系由一个张量给出，该张量描述了应力随深度的旋转和变化。涡动粘性的概念是适用的，如果粘性张量被用来联系应力和垂直剪切。粘性张量仅是垂直坐标的函数，与风应力无关。在15至20米深度显示最大值，可能是由于朗缪尔循环细胞。需要进一步的研究来确定这个张量的物理性质。它在混合层内部的星等超过1000 cgs单位。因此，埃克曼电流很弱，可能不是混合层内的主导电流。
Measurements made with satellite-tracked buoys drogued in different layers between the sea surface and 30-m depth under homogeneous winter conditions in the North Sea allow analysis of the Ekman currents under a large variety of wind conditions. The experiment lasted from November 20, 1991, until February 29, 1992. The first 4 weeks of this period, during which the buoys stayed close together, are used to determine the Ekman stresses. The total current field is a superposition of barotropic currents due to sea level variations and Ekman currents. The classical Ekman theory is not able to describe properly the observed deflection of the currents to the right of the wind direction and their decay with depth. This deflection is 10° near the sea surface and increases to approximately 50° in 25-m depth. The relation between wind stress and the stress field in the interior of the water is given by a tensor, which describes the rotation and the variation of the stress with increasing depth. The concept of eddy viscosity is applicable, if a viscosity tensor is used to relate stress and vertical shear. The viscosity tensor is a function of the vertical coordinate only and is independent from the wind stress. It shows maximum values in 15- to 20-m depth and may be due to Langmuir circulation cells. Further studies are needed to determine the physics of this tensor. Its magnitude in the interior of the mixed layer exceeds 1000 cgs units. Consequently, Ekman currents are weak and may not be the dominant currents within the mixed layer.