Changeset 6320 for trunk/DOC/TexFiles/Chapters/Chap_SBC.tex

Timestamp:

2016-02-17T16:24:34+01:00 (8 years ago)

Author:

mathiot

Message:

ISF: update documentation

File:

• trunk/DOC/TexFiles/Chapters/Chap_SBC.tex (modified) (3 diffs)

trunk/DOC/TexFiles/Chapters/Chap_SBC.tex

@@ -51 +51 @@
 \item the modification of fluxes below ice-covered areas (using observed ice-cover or a sea-ice model) (\np{nn\_ice}~=~0,1, 2 or 3) ; 
 \item the addition of river runoffs as surface freshwater fluxes or lateral inflow (\np{ln\_rnf}~=~true) ; 
-\item the addition of isf melting as lateral inflow (parameterisation) (\np{nn\_isf}~=~2 or 3 and \np{ln\_isfcav}~=~false) 
-or as fluxes applied at the land-ice ocean interface (\np{nn\_isf}~=~1 or 4 and \np{ln\_isfcav}~=~true) ; 
+\item the addition of isf melting as lateral inflow (parameterisation) or as fluxes applied at the land-ice ocean interface (\np{ln\_isf}) ; 
 \item the addition of a freshwater flux adjustment in order to avoid a mean sea-level drift (\np{nn\_fwb}~=~0,~1~or~2) ; 
 \item the transformation of the solar radiation (if provided as daily mean) into a diurnal cycle (\np{ln\_dm2dc}~=~true) ; 
@@ -924 +923 @@
 \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}, controls the ice shelf representation used. 
 \begin{description}
 \item[\np{nn\_isf}~=~1]
-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 ways 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. 
+The ice shelf cavity is represented (\np{ln\_isfcav}~=~true needed). The fwf and heat flux are computed. Two different bulk formula are available:
+   \begin{description}
+   \item[\np{nn\_isfblk}~=~1]
+   The bulk formula used to compute the melt is based the one described in \citet{Hunter2006}.
+        This formulation is based on a balance between the upward ocean heat flux and the latent heat flux at the ice shelf base.
+
+   \item[\np{nn\_isfblk}~=~2] 
+   The bulk formula used to compute the melt is based the one described in \citet{Jenkins1991}.
+        This formulation is based on a 3 equations formulation (a heat flux budget, a salt flux budget
+         and a linearised freezing point temperature equation).
+   \end{description}
+
+For this 2 bulk formulations, there are 3 different ways to compute the exchange coeficient:
+   \begin{description}
+        \item[\np{nn\_gammablk~=~0~}]
+   The salt and heat exchange coefficients are constant and defined by \np{rn\_gammas0} and \np{rn\_gammat0}
+
+   \item[\np{nn\_gammablk~=~1~}]
+   The salt and heat exchange coefficients are velocity dependent and defined as $\np{rn\_gammas0} \times u_{*}$ and $\np{rn\_gammat0} \times u_{*}$
+        where $u_{*}$ is the friction velocity in the top boundary layer (ie first \np{rn\_hisf\_tbl} meters).
+        See \citet{Jenkins2010} for all the details on this formulation.
+   
+   \item[\np{nn\_gammablk~=~2~}]
+   The salt and heat exchange coefficients are velocity and stability dependent and defined as 
+        $\gamma_{T,S} = \frac{u_{*}}{\Gamma_{Turb} + \Gamma^{T,S}_{Mole}}$
+        where $u_{*}$ is the friction velocity in the top boundary layer (ie first \np{rn\_hisf\_tbl} meters), 
+        $\Gamma_{Turb}$ the contribution of the ocean stability and 
+        $\Gamma^{T,S}_{Mole}$ the contribution of the molecular diffusion.
+        See \citet{Holland1999} for all the details on this formulation.
+        \end{description}
 
 \item[\np{nn\_isf}~=~2]
@@ -942 +961 @@
 The fwf is distributed along the ice shelf edge between the depth of the average grounding line (GL)
 (\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 and the exchange coefficients 
-are set as (\np{rn\_gammat0}) and (\np{rn\_gammas0}).
+Furthermore the fwf and heat flux are computed using the \citet{Beckmann2003} parameterisation of isf melting. 
+The effective melting length (\np{sn\_Leff\_isf}) is read from a file.
 
 \item[\np{nn\_isf}~=~3]
 A simple parameterisation of isf is used. The ice shelf cavity is not represented. 
-The fwf (\np{sn\_rnfisf}) is distributed along the ice shelf edge between the depth of the average grounding line (GL)
-(\np{sn\_depmax\_isf}) and the base of the ice shelf along the calving front (\np{sn\_depmin\_isf}).
-Full description, sensitivity and validation in preparation.
+The fwf (\np{sn\_rnfisf}) is prescribed and distributed along the ice shelf edge between the depth of the average grounding line (GL)
+(\np{sn\_depmax\_isf}) and the base of the ice shelf along the calving front (\np{sn\_depmin\_isf}). 
+The heat flux ($Q_h$) is computed as $Q_h = fwf \times L_f$.
 
 \item[\np{nn\_isf}~=~4]
-The ice shelf cavity is represented. However, the fwf (\np{sn\_fwfisf}) and heat flux (\np{sn\_qisf}) are 
-not computed but specified from file. 
+The ice shelf cavity is opened (\np{ln\_isfcav}~=~true needed). However, the fwf is not computed but specified from file \np{sn\_fwfisf}). 
+The heat flux ($Q_h$) is computed as $Q_h = fwf \times L_f$.\\
 \end{description}
 
-\np{nn\_isf}~=~1 and \np{nn\_isf}~=~2 compute a melt rate based on the water masse properties, ocean velocities and depth.
- This flux is thus highly dependent of the model resolution (horizontal and vertical), realism of the water masse onto the shelf ...
-
-\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.
-
+
+$\bullet$ \np{nn\_isf}~=~1 and \np{nn\_isf}~=~2 compute a melt rate based on the water mass properties, ocean velocities and depth.
+ This flux is thus highly dependent of the model resolution (horizontal and vertical), realism of the water masses onto the shelf ...\\
+
+
+$\bullet$ \np{nn\_isf}~=~3 and \np{nn\_isf}~=~4 read the melt rate from a file. You have total control of the fwf forcing.
 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. 
-
-\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. 
+coarse to have realistic melting or for studies where you need to control your heat and fw input.\\ 
+
+A namelist parameters control over how many meters the heat and fw fluxes are spread. 
+\np{rn\_hisf\_tbl}] is the top boundary layer thickness as defined in \citet{Losch2008}. 
+This parameter is only used if \np{nn\_isf}~=~1 or \np{nn\_isf}~=~4
+
+If \np{rn\_hisf\_tbl} = 0.0, the fluxes are put in the top level whatever is its tickness. 
+
+If \np{rn\_hisf\_tbl} $>$ 0.0, the fluxes are spread over the first \np{rn\_hisf\_tbl} m (ie over one or several cells).\\
+
+The ice shelf melt is implemented as a volume flux with in the same way as for the runoff.
+The fw 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}. 
+See the runoff section \ref{SBC_rnf} for all the details about the divergence correction. 
+
 
 \section{ Ice sheet coupling}