Changeset 11675 for NEMO/trunk/doc/latex/NEMO/subfiles/chap_ZDF.tex

Timestamp:

2019-10-11T00:15:18+02:00 (5 years ago)

Author:

agn

Message:

started on flux-gradient relationship

File:

• NEMO/trunk/doc/latex/NEMO/subfiles/chap_ZDF.tex (modified) (3 diffs)

NEMO/trunk/doc/latex/NEMO/subfiles/chap_ZDF.tex

@@ -548 +548 @@
 Much of the time the turbulent motions in the ocean surface boundary
 layer (OSBL) are not given by
-classical shear turbulence. Instead they are in a regime dominated by an
-interaction between the currents and the Stokes drift of the surface waves known as
-`Langmuir turbulence' \citep[e.g.][]{mcwilliams.ea_JFM97}.
+classical shear turbulence. Instead they are in a regime known as
+`Langmuir turbulence',  dominated by an
+interaction between the currents and the Stokes drift of the surface waves \citep[e.g.][]{mcwilliams.ea_JFM97}.
+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 $\mathrm{La}_{t}=(u_{\ast}/u_{s0}) > 0.4$.
+
 The OSMOSIS model is fundamentally based on results of Large Eddy
 Simulations (LES) of Langmuir turbulence and aims to fully describe
@@ -561 +563 @@
 $h_{\mathrm{BL}}$ and a turbulent velocity scale, is imposed throughout the 
 boundary layer
-$-h_{\mathrm{BL}}<z<\eta$.
-However, rather than the OSBL
+$-h_{\mathrm{BL}}<z<\eta$. The turbulent closure model
+also includes fluxes of tracers and momentum that are``non-local'' (independent of the local property gradient).
+
+Rather than the OSBL
 depth being diagnosed in terms of a bulk Richardson number criterion,
 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).
 
+
 \subsubsection{The flux gradient model}
-
-The turbulent closure model
-also includes ``non-local'' (independent of the local property gradient)
-fluxes of tracers and momentum.
+The flux-gradient relationships used in the OSMOSIS scheme take the form,
+\begin{equation}\label{eq:flux-grad-gen}
+\overline{w^\prime\chi^\prime}=-K\frac{\partial\overline{\chi}}{\partial z} + N_{\chi,s} +N_{\chi,b} +N_{\chi,t}
+\end{equation} 
+where $\chi$ is a general variable and $N_{\chi,s}, N_{\chi,b} \mathrm{and} N_{\chi,t}$  are the non-gradient terms, and represent the effects of the different terms in the turbulent flux-budget 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 flux-gradient relationship is used to parametrize the transports of momentum, heat and salinity.
+
 
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