Changeset 6225 for branches/2014/dev_r4704_NOC5_MPP_BDY_UPDATE/DOC/TexFiles/Chapters/Chap_SBC.tex

Timestamp:

2016-01-08T10:35:19+01:00 (8 years ago)

Author:

jamesharle

Message:

Update MPP_BDY_UPDATE branch to be consistent with head of trunk

File:

• branches/2014/dev_r4704_NOC5_MPP_BDY_UPDATE/DOC/TexFiles/Chapters/Chap_SBC.tex (modified) (6 diffs)

branches/2014/dev_r4704_NOC5_MPP_BDY_UPDATE/DOC/TexFiles/Chapters/Chap_SBC.tex

@@ -1 +1 @@
 % ================================================================
-% Chapter � Surface Boundary Condition (SBC, ICB) 
-% ================================================================
-\chapter{Surface Boundary Condition (SBC, ICB) }
+% Chapter � Surface Boundary Condition (SBC, ISF, ICB) 
+% ================================================================
+\chapter{Surface Boundary Condition (SBC, ISF, ICB) }
 \label{SBC}
 \minitoc
@@ -48 +48 @@
 below ice-covered areas (using observed ice-cover or a sea-ice model) 
 (\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 a freshwater flux adjustment 
-in order to avoid a mean sea-level drift (\np{nn\_fwb}~=~0,~1~or~2); the 
+fluxes or lateral inflow (\np{ln\_rnf}~=~true); the addition of isf melting as lateral inflow (parameterisation) 
+ 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 
 cycle (\np{ln\_dm2dc}~=~true); and a neutral drag coefficient can be read from an external wave 
@@ -60 +61 @@
 Finally, the different options that further modify the fluxes applied to the ocean are discussed.
 One of these is modification by icebergs (see \S\ref{ICB_icebergs}), which act as drifting sources of fresh water.
+Another example of modification is that due to the ice shelf melting/freezing (see \S\ref{SBC_isf}), 
+which provides additional sources of fresh water.
 
 
@@ -686 +689 @@
 air temperature, sea-surface temperature, cloud cover and relative humidity.
 Sensible heat and latent heat fluxes are computed by classical
-bulk formulae parameterized according to \citet{Kondo1975}.
+bulk formulae parameterised according to \citet{Kondo1975}.
 Details on the bulk formulae used can be found in \citet{Maggiore_al_PCE98} and \citet{Castellari_al_JMS1998}.
 
@@ -826 +829 @@
 \Pi-g\delta = (1+k-h) \Pi_{A}(\lambda,\phi)
 \end{equation}
-with $k$ a number of Love estimated to 0.6 which parametrized the astronomical tidal land,
-and $h$ a number of Love to 0.3 which parametrized the parametrization due to the astronomical tidal land.
+with $k$ a number of Love estimated to 0.6 which parameterised the astronomical tidal land,
+and $h$ a number of Love to 0.3 which parameterised the parameterisation due to the astronomical tidal land.
 
 % ================================================================
@@ -945 +948 @@
 
 %}
-
-
+% ================================================================
+%        Ice shelf melting
+% ================================================================
+\section   [Ice shelf melting (\textit{sbcisf})]
+                        {Ice shelf melting (\mdl{sbcisf})}
+\label{SBC_isf}
+%------------------------------------------namsbc_isf----------------------------------------------------
+\namdisplay{namsbc_isf}
+%--------------------------------------------------------------------------------------------------------
+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. 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. 
+
+\item[\np{nn\_isf}~=~2]
+A parameterisation of isf is used. The ice shelf cavity is not represented. 
+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}).
+
+\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.
+
+\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. 
+\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.
+
+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. 
+
+\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 $fields_b = fields_n$.
+%
 % ================================================================
 %        Handling of icebergs