Changeset 6306 for branches/2015

Timestamp:

2016-02-11T18:48:18+01:00 (8 years ago)

Author:

acc

Message:

Branch nemo_v3_6_STABLE (Documentation). Update Chap_ZDF.tex to include loglayer option for bottom friction. Also update namelist parameter references where names have changed

File:

• branches/2015/nemo_v3_6_STABLE/DOC/TexFiles/Chapters/Chap_ZDF.tex (modified) (7 diffs)

branches/2015/nemo_v3_6_STABLE/DOC/TexFiles/Chapters/Chap_ZDF.tex

@@ -261 +261 @@
 \end{equation}
 
-At the ocean surface, a non zero length scale is set through the  \np{rn\_lmin0} namelist 
+At the ocean surface, a non zero length scale is set through the  \np{rn\_mxl0} namelist 
 parameter. Usually the surface scale is given by $l_o = \kappa \,z_o$ 
 where $\kappa = 0.4$ is von Karman's constant and $z_o$ the roughness 
 parameter of the surface. Assuming $z_o=0.1$~m \citep{Craig_Banner_JPO94} 
-leads to a 0.04~m, the default value of \np{rn\_lsurf}. In the ocean interior 
+leads to a 0.04~m, the default value of \np{rn\_mxl0}. In the ocean interior 
 a minimum length scale is set to recover the molecular viscosity when $\bar{e}$ 
 reach its minimum value ($1.10^{-6}= C_k\, l_{min} \,\sqrt{\bar{e}_{min}}$ ).
@@ -294 +294 @@
 As the surface boundary condition on TKE is prescribed through $\bar{e}_o = e_{bb} |\tau| / \rho_o$, 
 with $e_{bb}$ the \np{rn\_ebb} namelist parameter, setting \np{rn\_ebb}~=~67.83 corresponds 
-to $\alpha_{CB} = 100$. further setting  \np{ln\_lsurf} to true applies \eqref{ZDF_Lsbc} 
-as surface boundary condition on length scale, with $\beta$ hard coded to the Stacet's value.
+to $\alpha_{CB} = 100$. Further setting  \np{ln\_mxl0} to true applies \eqref{ZDF_Lsbc} 
+as surface boundary condition on length scale, with $\beta$ hard coded to the Stacey's value.
 Note that a minimal threshold of \np{rn\_emin0}$=10^{-4}~m^2.s^{-2}$ (namelist parameters) 
 is applied on surface $\bar{e}$ value.
@@ -939 +939 @@
 $H = 4000$~m, the resulting friction coefficient is $r = 4\;10^{-4}$~m\;s$^{-1}$. 
 This is the default value used in \NEMO. It corresponds to a decay time scale 
-of 115~days. It can be changed by specifying \np{rn\_bfric1} (namelist parameter).
+of 115~days. It can be changed by specifying \np{rn\_bfri1} (namelist parameter).
 
 For the linear friction case the coefficients defined in the general 
@@ -949 +949 @@
 \end{split}
 \end{equation}
-When \np{nn\_botfr}=1, the value of $r$ used is \np{rn\_bfric1}. 
+When \np{nn\_botfr}=1, the value of $r$ used is \np{rn\_bfri1}. 
 Setting \np{nn\_botfr}=0 is equivalent to setting $r=0$ and leads to a free-slip 
 bottom boundary condition. These values are assigned in \mdl{zdfbfr}. 
@@ -956 +956 @@
 in the \ifile{bfr\_coef} input NetCDF file. The mask values should vary from 0 to 1. 
 Locations with a non-zero mask value will have the friction coefficient increased 
-by $mask\_value$*\np{rn\_bfrien}*\np{rn\_bfric1}.
+by $mask\_value$*\np{rn\_bfrien}*\np{rn\_bfri1}.
 
 % -------------------------------------------------------------------------------------------------------------
@@ -976 +976 @@
 $e_b = 2.5\;10^{-3}$m$^2$\;s$^{-2}$, while the FRAM experiment \citep{Killworth1992} 
 uses $C_D = 1.4\;10^{-3}$ and $e_b =2.5\;\;10^{-3}$m$^2$\;s$^{-2}$. 
-The CME choices have been set as default values (\np{rn\_bfric2} and \np{rn\_bfeb2} 
+The CME choices have been set as default values (\np{rn\_bfri2} and \np{rn\_bfeb2} 
 namelist parameters).
 
@@ -991 +991 @@
 \end{equation}
 
-The coefficients that control the strength of the non-linear bottom friction are 
-initialised as namelist parameters: $C_D$= \np{rn\_bfri2}, and $e_b$ =\np{rn\_bfeb2}. 
-Note for applications which treat tides explicitly a low or even zero value of 
-\np{rn\_bfeb2} is recommended. From v3.2 onwards a local enhancement of $C_D$ 
-is possible via an externally defined 2D mask array (\np{ln\_bfr2d}=true). 
-See previous section for details.
+The coefficients that control the strength of the non-linear bottom friction are
+initialised as namelist parameters: $C_D$= \np{rn\_bfri2}, and $e_b$ =\np{rn\_bfeb2}.
+Note for applications which treat tides explicitly a low or even zero value of
+\np{rn\_bfeb2} is recommended. From v3.2 onwards a local enhancement of $C_D$ is possible
+via an externally defined 2D mask array (\np{ln\_bfr2d}=true).  This works in the same way
+as for the linear bottom friction case with non-zero masked locations increased by
+$mask\_value$*\np{rn\_bfrien}*\np{rn\_bfri2}.
+
+% -------------------------------------------------------------------------------------------------------------
+%       Bottom Friction Log-layer
+% -------------------------------------------------------------------------------------------------------------
+\subsection{Log-layer Bottom Friction enhancement (\np{nn\_botfr} = 2, \np{ln\_loglayer} = .true.)}
+\label{ZDF_bfr_loglayer}
+
+In the non-linear bottom friction case, the drag coefficient, $C_D$, can be optionally
+enhanced using a "law of the wall" scaling. If  \np{ln\_loglayer} = .true., $C_D$ is no
+longer constant but is related to the thickness of the last wet layer in each column by:
+
+\begin{equation}
+C_D = \left ( {\kappa \over {\rm log}\left ( 0.5e_{3t}/rn\_bfrz0 \right ) } \right )^2
+\end{equation}
+
+\noindent where $\kappa$ is the von-Karman constant and \np{rn\_bfrz0} is a roughness
+length provided via the namelist.
+
+For stability, the drag coefficient is bounded such that it is kept greater or equal to
+the base \np{rn\_bfri2} value and it is not allowed to exceed the value of an additional
+namelist parameter: \np{rn\_bfri2\_max}, i.e.:
+
+\begin{equation}
+rn\_bfri2 \leq C_D \leq rn\_bfri2\_max
+\end{equation}
+
+\noindent Note also that a log-layer enhancement can also be applied to the top boundary
+friction if under ice-shelf cavities are in use (\np{ln\_isfcav}=.true.).  In this case, the
+relevant namelist parameters are \np{rn\_tfrz0}, \np{rn\_tfri2}
+and \np{rn\_tfri2\_max}.
 
 % -------------------------------------------------------------------------------------------------------------