Ekman spiral - Ekman spiral

Japanese: エクマンらせん - えくまんらせん

…On the ocean surface, the ocean current flows 45 degrees to the right, downwind, against the wind in the Northern Hemisphere (left in the Southern Hemisphere), and as the flow speed decreases with depth, the flow direction changes. The flow shown in Figure 2 is called the Ekman flow or Ekman spiral. The typical thickness of the Ekman flow (the depth at which the flow almost disappears) is expressed as, but even if A is the eddy viscosity coefficient, this value is only about 10 m in the real ocean, and it only accounts for a small part of the surface layer of the entire ocean depth. …

From [Atmospheric Boundary Layer]

...If we assume that K is constant regardless of height, that the average wind speed is 0 ( U = V = 0) at the surface ( z = 0), and that as the height increases ( z → ∞), the average wind speed becomes equal to the geostrophic wind ( U = Ug , V = Vg ) _, and solve the equation as shown in Figure 2. This is called _the Ekman spiral, and was first proposed by Swedish oceanographer VW Ekman in 1905 to explain the movement of ocean currents. Near the surface of the earth, there is a difference of about 45 degrees from the wind direction of the geostrophic wind, but in reality, the value is smaller than 45 degrees because it depends on the roughness of the earth's surface, the stability of the stratification, and the value of f . ...

*Some of the terminology that refers to the "Ekman spiral" is listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

Japanese:

…海面では海流が風に対し北半球では風下右方向(南半球なら左方向)に45度ずれて流れ，深さと共に流速が減ると同時に流向が変化していることがわかる。図2によって示される流れをエクマン流，またはエクマンらせんと呼ぶ。エクマン流の代表的な厚さ(ほとんど流れがなくなる深さ)はで表されるが，この値はAを渦粘性係数としても，現実の海ではたかだか10m程度で，海の深さ全体のうち表層のごく一部を占めているにすぎない。…

【大気境界層】より

…ここでKが高さに関係なく一定とし，地表(z＝0)で平均風速が0(U＝V＝0)，高さが高くなれば(z→∞)，平均風速は地衡風に等しくなる(U＝U_g,V＝V_g)として方程式を解くと図2のようになる。これはエクマンらせんと呼ばれ，スウェーデンの海洋学者V.W.エクマンが1905年に初めて海流の運動を説明するために提案したものである。地表面近くでは地衡風の風向と約45゜の差が生じているが，実際は，地表面の粗さ，成層の安定度およびfの値によって左右されることから，45゜より小さい値を示している。…