# Changeset 6320

Ignore:
Timestamp:
2016-02-17T16:24:34+01:00 (5 years ago)
Message:

ISF: update documentation

Location:
trunk/DOC/TexFiles
Files:
6 edited

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• ## trunk/DOC/TexFiles/Biblio/Biblio.bib

 r6289 pages = {1081--1098}, } @ARTICLE{Griffies_Hallberg_MWR00, author = {S.M. Griffies and R.H. Hallberg}, } @TechReport{Hunter2006, Title                    = {Specification for Test Models of Ice Shelf Cavities}, Author                   = {J. R. Hunter}, Institution              = {Antarctic Climate \& Ecosystems Cooperative Research Centre Private Bag 80, Hobart, Tasmania 7001}, Year                     = {2006}, } @TECHREPORT{TEOS10, author = {IOC and SCOR and IAPSO}, volume = {96},  number = {C11}, pages = {2298--2312} } @ARTICLE{Jenkins2001, author = {A. Jenkins}, title = {The Role of Meltwater Advection in the Formulation of Conservative Boundary Conditions at an Ice-Ocean Interface}, journal = JPO, year = {2001}, volume = {31}, pages = {285--296} }
• ## trunk/DOC/TexFiles/Chapters/Chap_DOM.tex

 r6289 in each water column is by-passed}. If \np{ln\_isfcav}~=~true, an extra file input file describing the ice shelf draft (in meters) (\ifile{isf\_draft\_meter}) is needed and all the location where the isf cavity thinnest than \np{rn\_isfhmin} meters are grounded ($i.e.$ masked). (in meters) (\ifile{isf\_draft\_meter}) is needed. After reading the bathymetry, the algorithm for vertical grid definition differs domain width at the central latitude. This is meant for the "EEL-R5" configuration, a periodic or open boundary channel with a seamount. \item[\np{nn\_bathy} = 1] read a bathymetry. The \ifile{bathy\_meter} file (Netcdf format) provides the ocean depth (positive, in meters) at each grid point of the model grid. The bathymetry is usually built by interpolating a standard bathymetry product \item[\np{nn\_bathy} = 1] read a bathymetry and ice shelf draft (if needed). The \ifile{bathy\_meter} file (Netcdf format) provides the ocean depth (positive, in meters) at each grid point of the model grid. The bathymetry is usually built by interpolating a standard bathymetry product ($e.g.$ ETOPO2) onto the horizontal ocean mesh. Defining the bathymetry also defines the coastline: where the bathymetry is zero, no model levels are defined (all levels are masked). The \ifile{isfdraft\_meter} file (Netcdf format) provides the ice shelf draft (positive, in meters) at each grid point of the model grid. This file is only needed if \np{ln\_isfcav}~=~true. Defining the ice shelf draft will also define the ice shelf edge and the grounding line position. \end{description} (Fig.~\ref{Fig_zgr}). If the ice shelf cavities are opened (\np{ln\_isfcav}=~true~}), the definition of $z_0$ is the same. However, definition of $e_3^0$ at $t$- and $w$-points is respectively changed to: \label{DOM_zgr_ana} \begin{split} e_3^T(k) &= z_W (k+1) - z_W (k)   \\ e_3^W(k) &= z_T (k)   - z_T (k-1) \\ \end{split} This formulation decrease the self-generated circulation into the ice shelf cavity (which can, in extreme case, leads to blow up).\\ The most used vertical grid for ORCA2 has $10~m$ ($500~m)$ resolution in the surface (bottom) layers and a depth which varies from 0 at the sea surface to a gives the number of ocean levels ($i.e.$ those that are not masked) at each $t$-point. mbathy is computed from the meter bathymetry using the definiton of gdept as the number of $t$-points which gdept $\leq$ bathy. gdept as the number of $t$-points which gdept $\leq$ bathy. Modifications of the model bathymetry are performed in the \textit{bat\_ctl} that do not communicate with another ocean point at the same level are eliminated. From the \textit{mbathy} array, the mask fields are defined as follows: In case of ice shelf cavities, as for the representation of bathymetry, a 2D integer array, misfdep, is created. misfdep defines the level of the first wet $t$-point (ie below the ice-shelf/ocean interface). All the cells between $k=1$ and $misfdep(i,j)-1$ are masked. By default, $misfdep(:,:)=1$ and no cells are masked. Modifications of the model bathymetry and ice shelf draft into the cavities are performed in the \textit{zgr\_isf} routine. The compatibility between ice shelf draft and bathymetry is checked. All the locations where the isf cavity is thinnest than \np{rn\_isfhmin} meters are grounded ($i.e.$ masked). If only one cell on the water column is opened at $t$-, $u$- or $v$-points, the bathymetry or the ice shelf draft is dug to fit this constrain. If the incompatibility is too strong (need to dig more than 1 cell), the cell is masked.\\ From the \textit{mbathy} and \textit{misfdep} array, the mask fields are defined as follows: \begin{align*} tmask(i,j,k) &= \begin{cases}   \; 1&   \text{ if $k\leq mbathy(i,j)$  }    \\ \; 0&   \text{ if $k\leq mbathy(i,j)$  }    \end{cases}     \\ tmask(i,j,k) &= \begin{cases}   \; 0&   \text{ if $k < misfdep(i,j)$ } \\ \; 1&   \text{ if $misfdep(i,j) \leq k\leq mbathy(i,j)$  }    \\ \; 0&   \text{ if $k > mbathy(i,j)$  }    \end{cases}     \\ umask(i,j,k) &=         \; tmask(i,j,k) \ * \ tmask(i+1,j,k)   \\ vmask(i,j,k) &=         \; tmask(i,j,k) \ * \ tmask(i,j+1,k)   \\ fmask(i,j,k) &=         \; tmask(i,j,k) \ * \ tmask(i+1,j,k)   \\ & \ \ \, * tmask(i,j,k) \ * \ tmask(i+1,j,k) & \ \ \, * tmask(i,j,k) \ * \ tmask(i+1,j,k) \\ wmask(i,j,k) &=         \; tmask(i,j,k) \ * \ tmask(i,j,k-1) \text{ with } wmask(i,j,1) = tmask(i,j,1) \end{align*} Note that \textit{wmask} is not defined as it is exactly equal to \textit{tmask} with the numerical indexing used (\S~\ref{DOM_Num_Index}). Moreover, the specification of closed lateral boundaries requires that at least the first and last Note, wmask is now defined. It allows, in case of ice shelves, to deal with the top boundary (ice shelf/ocean interface) exactly in the same way as for the bottom boundary. The specification of closed lateral boundaries requires that at least the first and last rows and columns of the \textit{mbathy} array are set to zero. In the particular case of an east-west cyclical boundary condition, \textit{mbathy} has its last
• ## trunk/DOC/TexFiles/Chapters/Chap_DYN.tex

 r6289 pressure Jacobian method is used to solve the horizontal pressure gradient. This method can provide a more accurate calculation of the horizontal pressure gradient than the standard scheme. \subsection{Ice shelf cavity} \label{DYN_hpg_isf} Beneath an ice shelf, the total pressure gradient is the sum of the pressure gradient due to the ice shelf load and the pressure gradient due to the ocean load. If cavity opened (\np{ln\_isfcav}~=~true) these 2 terms can be calculated by setting \np{ln\_dynhpg\_isf}~=~true. No other scheme are working with the ice shelf.\\ $\bullet$ The main hypothesis to compute the ice shelf load is that the ice shelf is in an isostatic equilibrium. The top pressure is computed integrating from surface to the base of the ice shelf a reference density profile (prescribed as density of a water at 34.4 PSU and -1.9$\degres C$) and corresponds to the water replaced by the ice shelf. This top pressure is constant over time. A detailed description of this method is described in \citet{Losch2008}.\\ $\bullet$ The ocean load is computed using the expression \eqref{Eq_dynhpg_sco} described in \ref{DYN_hpg_sco}. %--------------------------------------------------------------------------------------------------------------
• ## trunk/DOC/TexFiles/Chapters/Chap_SBC.tex

 r6289 \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) ; \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] 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}
• ## trunk/DOC/TexFiles/Chapters/Chap_TRA.tex

 r6289 (see \S\ref{SBC_rnf} for further detail of how it acts on temperature and salinity tendencies) $\bullet$ \textit{fwfisf}, the mass flux associated with ice shelf melt, (see \S\ref{SBC_isf} for further details on how the ice shelf melt is computed and applied). The surface boundary condition on temperature and salinity is applied as follows: \label{Eq_tra_sbc} I've changed "derivative" to "difference" and "mean" to "average"} With partial bottom cells (\np{ln\_zps}=true), in general, tracers in horizontally With partial cells (\np{ln\_zps}=true) at bottom and top (\np{ln\_isfcav}=true), in general, tracers in horizontally adjacent cells live at different depths. Horizontal gradients of tracers are needed for horizontal diffusion (\mdl{traldf} module) and for the hydrostatic pressure gradient (\mdl{dynhpg} module) to be active. gradient (\mdl{dynhpg} module) to be active. The partial cell properties at the top (\np{ln\_isfcav}=true) are computed in the same way as for the bottom. So, only the bottom interpolation is shown. \gmcomment{STEVEN from gm : question: not sure of  what -to be active- means} Before taking horizontal gradients between the tracers next to the bottom, a linear interpolation in the vertical is used to approximate the deeper tracer as if it actually
• ## trunk/DOC/TexFiles/Chapters/Chap_ZDF.tex

 r6289 % Bottom Friction % ================================================================ \section  [Bottom and top Friction (\textit{zdfbfr})]   {Bottom Friction (\mdl{zdfbfr} module)} \section  [Bottom and Top Friction (\textit{zdfbfr})]   {Bottom and Top Friction (\mdl{zdfbfr} module)} \label{ZDF_bfr} Options to define the top and bottom friction are defined through the  \ngn{nambfr} namelist variables. The top friction is activated only if the ice shelf cavities are opened (\np{ln\_isfcav}~=~true). As the friction processes at the top and bottom are the represented similarly, only the bottom friction is described in detail. The bottom friction represents the friction generated by the bathymetry. The top friction represents the friction generated by the ice shelf/ocean interface. As the friction processes at the top and bottom are represented similarly, only the bottom friction is described in detail below.\\ Both the surface momentum flux (wind stress) and the bottom momentum
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