Changeset 6808 for branches/NERC/dev_r5549_BDY_ZEROGRAD/DOC/TexFiles/Chapters/Chap_SBC.tex

Timestamp:

2016-07-19T10:38:35+02:00 (8 years ago)

Author:

jamesharle

Message:

merge with trunk@6232 for consistency with SSB code

File:

• branches/NERC/dev_r5549_BDY_ZEROGRAD/DOC/TexFiles/Chapters/Chap_SBC.tex (modified) (4 diffs)

branches/NERC/dev_r5549_BDY_ZEROGRAD/DOC/TexFiles/Chapters/Chap_SBC.tex

@@ -49 +49 @@
 (\np{nn\_ice}~=~0,1, 2 or 3); the addition of river runoffs as surface freshwater 
 fluxes or lateral inflow (\np{ln\_rnf}~=~true); the addition of isf melting as lateral inflow (parameterisation) 
-(\np{nn\_isf}~=~2 or 3 and \np{ln\_isfcav}~=~false) or as surface flux at the land-ice ocean interface
-(\np{nn\_isf}~=~1 or 4 and \np{ln\_isfcav}~=~true); 
+ or as surface flux at the land-ice ocean interface (\np{ln\_isf}=~true); 
 the addition of a freshwater flux adjustment in order to avoid a mean sea-level drift (\np{nn\_fwb}~=~0,~1~or~2); the 
 transformation of the solar radiation (if provided as daily mean) into a diurnal 
@@ -958 +957 @@
 \namdisplay{namsbc_isf}
 %--------------------------------------------------------------------------------------------------------
-Namelist variable in \ngn{namsbc}, \np{nn\_isf},  control the kind of ice shelf representation used. 
+Namelist variable in \ngn{namsbc}, \np{nn\_isf}, control the kind of ice shelf representation used. 
 \begin{description}
 \item[\np{nn\_isf}~=~1]
-The ice shelf cavity is represented. The fwf and heat flux are computed. 
+The ice shelf cavity is represented. The fwf and heat flux are computed. 2 bulk formulations are available: the ISOMIP one (\np{nn\_isfblk = 1}) described in (\np{nn\_isfblk = 2}), the 3 equation formulation described in \citet{Jenkins1991}. In addition to this, 
+3 different way to compute the exchange coefficient are available. $\gamma\_{T/S}$ is constant (\np{nn\_gammablk = 0}), $\gamma\_{T/S}$ is velocity dependant \citep{Jenkins2010} (\np{nn\_gammablk = 1}) and $\gamma\_{T/S}$ is velocity dependant and stratification dependent \citep{Holland1999} (\np{nn\_gammablk = 2}). For each of them, the thermal/salt exchange coefficient (\np{rn\_gammat0} and \np{rn\_gammas0}) have to be specified (the default values are for the ISOMIP case). 
 Full description, sensitivity and validation in preparation. 
 
@@ -969 +969 @@
 (\np{sn\_depmax\_isf}) and the base of the ice shelf along the calving front (\np{sn\_depmin\_isf}) as in (\np{nn\_isf}~=~3). 
 Furthermore the fwf is computed using the \citet{Beckmann2003} parameterisation of isf melting. 
-The effective melting length (\np{sn\_Leff\_isf}) is read from a file.
+The effective melting length (\np{sn\_Leff\_isf}) is read from a file and the exchange coefficients are set as (\np{rn\_gammat0}) and (\np{rn\_gammas0}).
 
 \item[\np{nn\_isf}~=~3]
@@ -987 +987 @@
 \np{nn\_isf}~=~3 and \np{nn\_isf}~=~4 read the melt rate and heat flux from a file. You have total control of the fwf scenario.
 
- This can be usefull if the water masses on the shelf are not realistic or the resolution (horizontal/vertical) are too 
+This can be usefull if the water masses on the shelf are not realistic or the resolution (horizontal/vertical) are too 
 coarse to have realistic melting or for sensitivity studies where you want to control your input. 
 Full description, sensitivity and validation in preparation. 
 
-There is 2 ways to apply the fwf to NEMO. The first possibility (\np{ln\_divisf}~=~false) applied the fwf
- and heat flux directly on the salinity and temperature tendancy. The second possibility (\np{ln\_divisf}~=~true)
- apply the fwf as for the runoff fwf (see \S\ref{SBC_rnf}). The mass/volume addition due to the ice shelf melting is,
- at each relevant depth level, added to the horizontal divergence (\textit{hdivn}) in the subroutine \rou{sbc\_isf\_div} 
-(called from \mdl{divcur}). 
+\np{rn\_hisf\_tbl} is the top boundary layer (tbl) thickness used by the Losch parametrisation \citep{Losch2008} to compute the melt. if 0, temperature/salt/velocity in the top cell is used to compute the melt.
+Otherwise, NEMO used the mean value into the tbl. 
+
+\section{ Ice sheet coupling}
+\label{SBC_iscpl}
+%------------------------------------------namsbc_iscpl----------------------------------------------------
+\namdisplay{namsbc_iscpl}
+%--------------------------------------------------------------------------------------------------------
+Ice sheet/ocean coupling is done through file exchange at the restart step. NEMO, at each restart step, 
+read the bathymetry and ice shelf draft variable in a netcdf file. 
+If \np{ln\_iscpl = ~true}, the isf draft is assume to be different at each restart step 
+with potentially some new wet/dry cells due to the ice sheet dynamics/thermodynamics.
+The wetting and drying scheme applied on the restart is very simple and described below for the 6 different cases:
+\begin{description}
+\item[Thin a cell down:]
+   T/S/ssh are unchanged and U/V in the top cell are corrected to keep the barotropic transport (bt) constant ($bt_b=bt_n$).
+\item[Enlarge  a cell:]
+   See case "Thin a cell down"
+\item[Dry a cell:]
+   mask, T/S, U/V and ssh are set to 0. Furthermore, U/V into the water column are modified to satisfy ($bt_b=bt_n$).
+\item[Wet a cell:] 
+   mask is set to 1, T/S is extrapolated from neighbours, $ssh_n = ssh_b$ and U/V set to 0. If no neighbours along i,j and k, T/S/U/V and mask are set to 0.
+\item[Dry a column:]
+   mask, T/S, U/V are set to 0 everywhere in the column and ssh set to 0.
+\item[Wet a column:]
+   set mask to 1, T/S is extrapolated from neighbours, ssh is extrapolated from neighbours and U/V set to 0. If no neighbour, T/S/U/V and mask set to 0.
+\end{description}
+The extrapolation is call \np{nn\_drown} times. It means that if the grounding line retreat by more than \np{nn\_drown} cells between 2 coupling steps,
+ the code will be unable to fill all the new wet cells properly. The default number is set up for the MISOMIP idealised experiments.\\
+This coupling procedure is able to take into account grounding line and calving front migration. However, it is a non-conservative processe. 
+This could lead to a trend in heat/salt content and volume. In order to remove the trend and keep the conservation level as close to 0 as possible,
+ a simple conservation scheme is available with \np{ln\_hsb = ~true}. The heat/salt/vol. gain/loss is diagnose, as well as the location. 
+Based on what is done on sbcrnf to prescribed a source of heat/salt/vol., the heat/salt/vol. gain/loss is removed/added,
+ over a period of \np{rn\_fiscpl} time step, into the system. 
+So after \np{rn\_fiscpl} time step, all the heat/salt/vol. gain/loss due to extrapolation process is canceled.\\
+
+As the before and now fields are not compatible (modification of the geometry), the restart time step is prescribed to be an euler time step instead of a leap frog and $fields_b = fields_n$.
 %
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