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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 neutral density ： ウィキペディア英語版 neutral density The neutral density ( $\backslash gamma^n\backslash ,$ ) is a variable used in oceanography, introduced in 1997 by David R. Jackett and Trevor J. McDougall.〔Jackett, David R., Trevor J. McDougall, 1997: A Neutral Density Variable for the World's Oceans. J. Phys. Oceanogr., 27, 237–263〕 It is function of the three state variables (salinity, temperature, and pressure) and the geographical location (longitude and latitude) and it has the typical units of density (M/V). The level surfaces of $\backslash gamma^n\backslash ,$ form the “neutral density surfaces”, which are the most natural layer interfaces stratifying the deep ocean circulation, along which the strong lateral mixing in the ocean occurs. These surfaces are used in the analyses of ocean data and to perform models of the ocean circulation. The formation of neutral density surfaces from a given hydrographic observation requires only a call to a computational code (available for Matlab and Fortran), that contains the computational algorithm developed by Jackett and McDougall. == Mathematical expression == A neutral density surface is the surface along which a given water mass will move, remaining neutrally buoyant.〔 McDougall and Jackett 〔McDougall, T. J. and D. R. Jackett, 1988: On the helical nature of neutral surfaces. Progress in Oceanography, Vol. 20, Pergamon, 153–183〕 demonstrated that the normal to the neutral surfaces is in the direction of $\backslash beta\; \backslash nabla\; S\; -\; \backslash alpha\; \backslash nabla\; \backslash theta$, where S is the salinity, $\backslash theta\; \backslash ,$ is the potential temperature, $\backslash alpha\; \backslash ,$ the thermal expansion coefficient and $\backslash beta\; \backslash ,$ the saline concentration coefficient. Thus, neutral surfaces are defined as the surfaces everywhere perpendicular to the vector $\backslash rho\; (\backslash beta\; \backslash nabla\; S\; -\; \backslash alpha\; \backslash nabla\; \backslash theta)$. For such a surface to exist, its helicity H must be zero;〔Jackett, David R., Trevor J. McDougall, 1997: A Neutral Density Variable for the World's Oceans. J. Phys. Oceanogr., 27, page 238〕 if this condition is respected, a scalar $\backslash gamma^n\backslash ,$ exists and it is the one which satisfies the following formula:〔 :$\backslash nabla\backslash gamma^n\backslash \; =\; b\; \backslash rho\; (\backslash beta\; \backslash nabla\; S\; -\; \backslash alpha\; \backslash nabla\; \backslash theta);$ where b is an integrating scalar factor, which is function of space. This formula represents a coupled system of first-order partial differential equations, that has to be solved to obtain the desired value of $\backslash gamma^n\backslash ,$. The solutions of ( ) can be obtained by using numerical techniques. In the real ocean, the condition of helicity equal to zero is not generally satisfied exactly. Therefore, and because of the non-linear terms in the equation of state, it is impossible to create analytically a Well-defined neutral density surface.〔Klocker et all., 2007, “Diapycnal motion due to neutral helicity”〕 There will always be flow through the calculated surfaces, because of the presence of a neutral helicity. Therefore, it is possible to obtain only a best-fit approximate neutral surface, through which there is no flow of major proportions and along which it is generally accepted that flow takes place. $\backslash gamma^n\backslash ,$ is a Well-defined function and Jackett and McDougall demonstrated that the inaccuracy due to the not exact neutrality is below the present instrumentation error in density.〔Jackett, David R., Trevor J. McDougall, 1997: A Neutral Density Variable for the World's Oceans. J. Phys. Oceanogr., 27, page 239〕 Neutral density surfaces stay within a few tens meters of an ideal surface anywhere in the world. For how $\backslash gamma^n\backslash ,$ has been defined, neutral density surfaces can be considered the continuous analog of the commonly used potential density surfaces, which are defined over various discrete values of pressures (see for example 〔Montgomery, R. B., 1938: Circulation in the upper layers of the southern North Atlantic, Pap. Phys. Oceanogr. Meteor., 6(2), 55 pp.〕 and 〔Reid, J. L., 1994: On the total geostrophic circulation of the North Atlantic Ocean: Flow patterns, tracers and transports. Progress in Oceanography,Vol. 33, Pergamon, 1–92〕). 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「neutral density」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.