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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Langmuir circulation ： ウィキペディア英語版 Langmuir circulation In physical oceanography, Langmuir circulation consists of a series of shallow, slow, counter-rotating vortices at the ocean's surface aligned with the wind. These circulations are developed when wind blows steadily over the sea surface. Irving Langmuir discovered this phenomenon after observing windrows of seaweed in the Sargasso Sea in 1927.〔 〕 Langmuir circulations circulate within the mixed layer; however, it is not yet so clear how strongly they can cause mixing at the base of the mixed layer. 〔 〕 == Theory == The driving force of these circulations is an interaction of the mean flow with wave averaged flows of the surface waves. Stokes drift velocity of the waves stretches and tilts the vorticity of the flow near the surface. The production of vorticity in the upper ocean is balanced by downward (often turbulent) diffusion $\backslash nu\_T$. For a flow driven by a wind $\backslash tau$ characterized by friction velocity $u\_$ * the ratio of vorticity diffusion and production defines the Langmuir number 〔 : $$ \mathrm = \sqrt} \ \mathrm\ \sqrt} where the first definition is for a monochromatic wave field of amplitude $a$, frequency $\backslash sigma$, and wavenumber $k$ and the second uses a generic inverse length scale $\backslash beta$, and Stokes velocity scale $S\_0$. This is exemplified by the Craik-Leibovich equations〔 〕 which are an approximation of the Lagrangian mean 〔 〕 .〔 〕 In the Boussinesq approximation the governing equations can be written : $$ \frac +u_j\nabla_ju_i = \begin -2\epsilon_\Omega_j\left(u^s_k+u_k\right) -\nabla_i\left(\frac+\fracu^s_ju^s_j+u^s_ju_j\right)\\ +\epsilon_u^s_j\epsilon_\nabla_lu_m +g_i\frac +\nabla_j\nu\nabla_ju_i \end : $$ \nabla_iu_i=0 : $$ \frac +u_j\nabla_j\rho = \nabla_i\kappa\nabla_i\rho where $u\_i$ is the fluid velocity, $\backslash Omega$ is planetary rotation, $u^s\_i$ is the stokes drift velocity of the surface wave field, $P$ is the pressure, $g\_i$ is the acceleration due to gravity, $\backslash rho$ is the density, $\backslash rho\_0$ is the reference density, $\backslash nu$ is the viscosity, and $\backslash kappa$ is the diffusivity. In the open ocean conditions where there may not be a dominant length scale controlling the scale of the Langmuir cells the concept of Langmuir Turbulence is advanced. 〔 〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Langmuir circulation」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.