Changeset 1224 for trunk/DOC/TexFiles/Chapters/Chap_SBC.tex

Timestamp:

2008-11-26T14:52:28+01:00 (15 years ago)

Author:

gm

Message:

minor corrections in the Chapters from Steven + gm see ticket #283

File:

• trunk/DOC/TexFiles/Chapters/Chap_SBC.tex (modified) (4 diffs)

trunk/DOC/TexFiles/Chapters/Chap_SBC.tex

@@ -404 +404 @@
 %        Handling of ice-covered area
 % -------------------------------------------------------------------------------------------------------------
-\subsection{Handling of ice-covered area}
+\subsection{Handling of ice-covered area  (\textit{sbcice\_...})}
 \label{SBC_ice-cover}
 
@@ -411 +411 @@
 depending on the value of the \np{nn{\_}ice} namelist parameter.  
 \begin{description}
-\item[nn{\_}ice = 0]  there will never be sea-ice in the computational domain. This is a typical namelist value used for tropical ocean domain. The surface fluxes are simply specified for an ice-free ocean. No specific things are done for sea-ice.
-\item[nn{\_}ice = 1]  sea-ice can exist in the computational domain, but no sea-ice model is used. An observed ice covered area is read in a file. Below this area, the SST is restored to the freezing point and the heat fluxes are set to $-4~W/m^2$ ($-2~W/m^2$) in the northern (southern) hemisphere. The associated modification of the freshwater fluxes are done in such a way that the change in buoyancy fluxes remains zero. This prevents deep convection to occur when trying to reach the freezing point (and so ice covered area condition) while the SSS is too large. This manner of managing sea-ice area, just by using si IF case, is usually referred as the \textit{ice-if} model. It can be found in the \mdl{sbcice{\_}if} module.
-\item[nn{\_}ice = 2 or more]  A full sea ice model is used. This model computes the ice-ocean fluxes, that are combined with the air-sea fluxes using the ice fraction of each model cell to provide the surface ocean fluxes. Note that the activation of a sea-ice model is is done by defining a CPP key (\key{lim2} or \key{lim3}). The activation automatically ovewrite the read value of nn{\_}ice to its appropriate value ($i.e.$ $2$ for LIM-2 and $3$ for LIM-3).
+\item[nn{\_}ice = 0]  there will never be sea-ice in the computational domain. 
+This is a typical namelist value used for tropical ocean domain. The surface fluxes 
+are simply specified for an ice-free ocean. No specific things is done for sea-ice.
+\item[nn{\_}ice = 1]  sea-ice can exist in the computational domain, but no sea-ice model 
+is used. An observed ice covered area is read in a file. Below this area, the SST is 
+restored to the freezing point and the heat fluxes are set to $-4~W/m^2$ ($-2~W/m^2$) 
+in the northern (southern) hemisphere. The associated modification of the freshwater 
+fluxes are done in such a way that the change in buoyancy fluxes remains zero. 
+This prevents deep convection to occur when trying to reach the freezing point 
+(and so ice covered area condition) while the SSS is too large. This manner of 
+managing sea-ice area, just by using si IF case, is usually referred as the \textit{ice-if} 
+model. It can be found in the \mdl{sbcice{\_}if} module.
+\item[nn{\_}ice = 2 or more]  A full sea ice model is used. This model computes the 
+ice-ocean fluxes, that are combined with the air-sea fluxes using the ice fraction of 
+each model cell to provide the surface ocean fluxes. Note that the activation of a 
+sea-ice model is is done by defining a CPP key (\key{lim2} or \key{lim3}). 
+The activation automatically ovewrite the read value of nn{\_}ice to its appropriate 
+value ($i.e.$ $2$ for LIM-2 and $3$ for LIM-3).
 \end{description}
 
@@ -428 +443 @@
 %-------------------------------------------------------------------------------------------------------------
 
+The river runoffs 
+
 It is convenient to introduce the river runoff in the model as a surface 
 fresh water flux. 
 
+
+%Griffies:  River runoff generally enters the ocean at a nonzero depth rather than through the surface. Many global models, however, have traditionally inserted river runoff to the top model cell. Such can become problematic numerically and physically when the top grid cells are reÞned to levels common in coastal modelling. Hence, more applications are now considering the input of runoff throughout a nonzero depth. Likewise, sea ice can melt at depth, thus necessitating a mass transport to occur within the ocean between the liquid and solid water masses.
+
 \colorbox{yellow}{Nevertheless, Pb of vertical resolution and increase of Kz in vicinity of }
 
 \colorbox{yellow}{river mouths{\ldots}}
 
-Control of the mean sea level
+%IF( ln_rnf ) THEN                                     ! increase diffusivity at rivers mouths
+%        DO jk = 2, nkrnf   ;   avt(:,:,jk) = avt(:,:,jk) + rn_avt_rnf * rnfmsk(:,:)   ;   END DO
+%ENDIF
+
+
 
 % -------------------------------------------------------------------------------------------------------------
@@ -444 +468 @@
 \label{SBC_fwb}
 
-To be written later...
-
-\gmcomment{The descrition of the technique used to control the freshwater budget has to be added here}
-
-
-
-
+For global ocean simulation it can be useful to introduce a control of the mean sea 
+level in order to prevent unrealistic drift of the sea surface height due to inaccuracy 
+in the freshwater fluxes. In \NEMO, two way of controlling the the freshwater budget. 
+\begin{description}
+\item[\np{nn\_fwb}=0]  no control at all. The mean sea level is free to drift, and will 
+certainly do so.
+\item[\np{nn\_fwb}=1]  global mean EMP set to zero at each model time step. 
+%Note that with a sea-ice model, this technique only control the mean sea level with linear free surface (\key{vvl} not defined) and no mass flux between ocean and ice (as it is implemented in the current ice-ocean coupling). 
+\item[\np{nn\_fwb}=2]  freshwater budget is adjusted from the previous year annual 
+mean budget which is read in the \textit{EMPave\_old.dat} file. As the model uses the 
+Boussinesq approximation, the annual mean fresh water budget is simply evaluated 
+from the change in the mean sea level at January the first and saved in the 
+\textit{EMPav.dat} file. 
+\end{description}
+
+% Griffies doc:
+% When running ocean-ice simulations, we are not explicitly representing land processes, such as rivers, catchment areas, snow accumulation, etc. However, to reduce model drift, it is important to balance the hydrological cycle in ocean-ice models. We thus need to prescribe some form of global normalization to the precipitation minus evaporation plus river runoff. The result of the normalization should be a global integrated zero net water input to the ocean-ice system over a chosen time scale. 
+%How often the normalization is done is a matter of choice. In mom4p1, we choose to do so at each model time step, so that there is always a zero net input of water to the ocean-ice system. Others choose to normalize over an annual cycle, in which case the net imbalance over an annual cycle is used to alter the subsequent yearÕs water budget in an attempt to damp the annual water imbalance. Note that the annual budget approach may be inappropriate with interannually varying precipitation forcing. 
+%When running ocean-ice coupled models, it is incorrect to include the water transport between the ocean and ice models when aiming to balance the hydrological cycle. The reason is that it is the sum of the water in the ocean plus ice that should be balanced when running ocean-ice models, not the water in any one sub-component. As an extreme example to illustrate the issue, consider an ocean-ice model with zero initial sea ice. As the ocean-ice model spins up, there should be a net accumulation of water in the growing sea ice, and thus a net loss of water from the ocean. The total water contained in the ocean plus ice system is constant, but there is an exchange of water between the subcomponents. This exchange should not be part of the normalization used to balance the hydrological cycle in ocean-ice models. 
+
+
+