Changeset 11675
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 20191011T00:15:18+02:00 (5 years ago)
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NEMO/trunk/doc/latex/NEMO/subfiles/chap_ZDF.tex
r11674 r11675 548 548 Much of the time the turbulent motions in the ocean surface boundary 549 549 layer (OSBL) are not given by 550 classical shear turbulence. Instead they are in a regime dominated by an 551 interaction between the currents and the Stokes drift of the surface waves known as 552 `Langmuir turbulence' \citep[e.g.][]{mcwilliams.ea_JFM97}. 550 classical shear turbulence. Instead they are in a regime known as 551 `Langmuir turbulence', dominated by an 552 interaction between the currents and the Stokes drift of the surface waves \citep[e.g.][]{mcwilliams.ea_JFM97}. 553 This regime is characterised by strong vertical turbulent motion, and appears when the surface Stokes drift $u_{s0}$ is much greater than the friction velocity $u_{\ast}$. More specifically Langmuir turbulence is thought to be crucial where the turbulent Langmuir number $\mathrm{La}_{t}=(u_{\ast}/u_{s0}) > 0.4$. 554 553 555 The OSMOSIS model is fundamentally based on results of Large Eddy 554 556 Simulations (LES) of Langmuir turbulence and aims to fully describe … … 561 563 $h_{\mathrm{BL}}$ and a turbulent velocity scale, is imposed throughout the 562 564 boundary layer 563 $h_{\mathrm{BL}}<z<\eta$. 564 However, rather than the OSBL 565 $h_{\mathrm{BL}}<z<\eta$. The turbulent closure model 566 also includes fluxes of tracers and momentum that are``nonlocal'' (independent of the local property gradient). 567 568 Rather than the OSBL 565 569 depth being diagnosed in terms of a bulk Richardson number criterion, 566 570 as in KPP, it is set by a prognostic equation that is informed by … … 570 574 of the pycnocline (the stratified region at the bottom of the OSBL). 571 575 576 572 577 \subsubsection{The flux gradient model} 573 574 The turbulent closure model 575 also includes ``nonlocal'' (independent of the local property gradient) 576 fluxes of tracers and momentum. 578 The fluxgradient relationships used in the OSMOSIS scheme take the form, 579 \begin{equation}\label{eq:fluxgradgen} 580 \overline{w^\prime\chi^\prime}=K\frac{\partial\overline{\chi}}{\partial z} + N_{\chi,s} +N_{\chi,b} +N_{\chi,t} 581 \end{equation} 582 where $\chi$ is a general variable and $N_{\chi,s}, N_{\chi,b} \mathrm{and} N_{\chi,t}$ are the nongradient terms, and represent the effects of the different terms in the turbulent fluxbudget on the transport of $\chi$. $N_{\chi,s}$ represents the effects that the Stokes shear has on the transport of $\chi$, $N_{\chi,b}$ the effect of buoyancy, and $N_{\chi,t}$ the effect of the turbulent transport. The same general form for the fluxgradient relationship is used to parametrize the transports of momentum, heat and salinity. 583 577 584 578 585 %% =================================================================================================
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