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- 2011-12-20T12:39:04+01:00 (12 years ago)
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branches/2011/dev_NEMO_MERGE_2011/DOC/TexFiles/Chapters/Chap_LBC.tex
r3221 r3228 742 742 743 743 %-----------------------------------------nambdy-------------------------------------------- 744 %- cn_mask = '' ! name of mask file (if ln_bdy_mask=.TRUE.)745 %- cn_dta_frs_T = 'bdydata_grid_T.nc' ! name of data file (T-points)746 %- cn_dta_frs_U = 'bdydata_grid_U.nc' ! name of data file (U-points)747 %- cn_dta_frs_V = 'bdydata_grid_V.nc' ! name of data file (V-points)748 %- cn_dta_fla_T = 'bdydata_bt_grid_T.nc' ! name of data file for Flather condition (T-points)749 %- cn_dta_fla_U = 'bdydata_bt_grid_U.nc' ! name of data file for Flather condition (U-points)750 %- cn_dta_fla_V = 'bdydata_bt_grid_V.nc' ! name of data file for Flather condition (V-points)751 %- ln_clim = .false. ! contain 1 (T) or 12 (F) time dumps and be cyclic752 %- ln_vol = .true. ! total volume correction (see volbdy parameter)753 %- ln_mask = .false. ! boundary mask from filbdy_mask (T) or boundaries are on edges of domain (F)754 %- ln_tides = .true. ! Apply tidal harmonic forcing with Flather condition755 %- ln_dyn_fla = .true. ! Apply Flather condition to velocities756 %- ln_tra_frs = .false. ! Apply FRS condition to temperature and salinity757 %- ln_dyn_frs = .false. ! Apply FRS condition to velocities758 %- nn_rimwidth = 9 ! width of the relaxation zone759 %- nn_dtactl = 1 ! = 0, bdy data are equal to the initial state760 %- ! = 1, bdy data are read in 'bdydata .nc' files761 %- nn_volctl = 0 ! = 0, the total water flux across open boundaries is zero762 %- ! = 1, the total volume of the system is conserved763 744 \namdisplay{nambdy} 745 %----------------------------------------------------------------------------------------------- 746 %-----------------------------------------nambdy_index-------------------------------------------- 747 \namdisplay{nambdy_index} 748 %----------------------------------------------------------------------------------------------- 749 %-----------------------------------------nambdy_dta-------------------------------------------- 750 \namdisplay{nambdy_dta} 751 %----------------------------------------------------------------------------------------------- 752 %-----------------------------------------nambdy_dta-------------------------------------------- 753 \namdisplay{nambdy_dta2} 764 754 %----------------------------------------------------------------------------------------------- 765 755 … … 774 764 The BDY module was modelled on the OBC module and shares many features 775 765 and a similar coding structure \citep{Chanut2005}. 766 767 The BDY module is completely rewritten at NEMO 3.4 and there is a new 768 set of namelists. Boundary data files used with earlier versions of 769 NEMO may need to be re-ordered to work with this version. See the 770 section on the Input Boundary Data Files for details. 771 772 %---------------------------------------------- 773 \subsection{The namelists} 774 \label{BDY_namelist} 775 776 It is possible to define more than one boundary ``set'' and apply 777 different boundary conditions to each set. The number of boundary 778 sets is defined by \np{nb\_bdy}. Each boundary set may be defined 779 as a set of straight line segments in a namelist 780 (\np{ln\_coords\_file}=.false.) or read in from a file 781 (\np{ln\_coords\_file}=.true.). If the set is defined in a namelist, 782 then the namelists nambdy\_index must be included separately, one for 783 each set. If the set is defined by a file, then a 784 ``coordinates.bdy.nc'' file must be provided. The coordinates.bdy file 785 is analagous to the usual NEMO ``coordinates.nc'' file. In the example 786 above, there are two boundary sets, the first of which is defined via 787 a file and the second is defined in a namelist. For more details of 788 the definition of the boundary geometry see section 789 \ref{BDY_geometry}. 790 791 For each boundary set a boundary 792 condition has to be chosen for the barotropic solution (``u2d'': 793 sea-surface height and barotropic velocities), for the baroclinic 794 velocities (``u3d''), and for the active tracers\footnote{The BDY 795 module does not deal with passive tracers at this version} 796 (``tra''). For each set of variables there is a choice of algorithm 797 and a choice for the data, eg. for the active tracers the algorithm is 798 set by \np{nn\_tra} and the choice of data is set by 799 \np{nn\_tra\_dta}. 800 801 The choice of algorithm is currently as follows: 802 803 \mbox{} 804 805 \begin{itemize} 806 \item[0.] No boundary condition applied. So the solution will ``see'' 807 the land points around the edge of the edge of the domain. 808 \item[1.] Flow Relaxation Scheme (FRS) available for all variables. 809 \item[2.] Flather radiation scheme for the barotropic variables. The 810 Flather scheme is not compatible with the filtered free surface 811 ({\it dynspg\_ts}). 812 \end{itemize} 813 814 \mbox{} 815 816 The main choice for the boundary data is 817 to use initial conditions as boundary data (\np{nn\_tra\_dta}=0) or to 818 use external data from a file (\np{nn\_tra\_dta}=1). For the 819 barotropic solution there is also the option to use tidal 820 harmonic forcing either by itself or in addition to other external 821 data. 822 823 If external boundary data is required then the nambdy\_dta namelist 824 must be defined. One nambdy\_dta namelist is required for each boundary 825 set in the order in which the boundary sets are defined in nambdy. In 826 the example given, two boundary sets have been defined and so there 827 are two nambdy\_dta namelists. The boundary data is read in using the 828 fldread module, so the nambdy\_dta namelist is in the format required 829 for fldread. For each variable required, the filename, the frequency 830 of the files and the frequency of the data in the files is given. Also 831 whether or not time-interpolation is required and whether the data is 832 climatological (time-cyclic) data. Note that on-the-fly spatial 833 interpolation of boundary data is not available at this version. 834 835 In the example namelists given, two boundary sets are defined. The 836 first set is defined via a file and applies FRS conditions to 837 temperature and salinity and Flather conditions to the barotropic 838 variables. External data is provided in daily files (from a 839 large-scale model). Tidal harmonic forcing is also used. The second 840 set is defined in a namelist. FRS conditions are applied on 841 temperature and salinity and climatological data is read from external 842 files. 776 843 777 844 %---------------------------------------------- … … 832 899 Note that the sea-surface height gradient in \eqref{Eq_bdy_fla1} 833 900 is a spatial gradient across the model boundary, so that $\eta_{e}$ is 834 defined on the $T$ points with $nbrdta=1$ and $\eta$ is defined on the 835 $T$ points with $nbrdta=2$. $U$ and $U_{e}$ are defined on the $U$ or 836 $V$ points with $nbrdta=1$, $i.e.$ between the two $T$ grid points. 837 838 %---------------------------------------------- 839 \subsection{Choice of schemes} 840 \label{BDY_choice_of_schemes} 841 842 The Flow Relaxation Scheme may be applied separately to the 843 temperature and salinity (\np{ln\_tra\_frs} = true) and 844 the velocity fields (\np{ln\_dyn\_frs} = true). Flather 845 radiation conditions may be applied using externally defined 846 barotropic velocities and sea-surface height (\np{ln\_dyn\_fla} = true) 847 or using tidal harmonics fields (\np{ln\_tides} = true) 848 or both. FRS and Flather conditions may be applied simultaneously. 849 A typical configuration where all possible conditions might be used is a tidal, 850 shelf-seas model, where the barotropic boundary conditions are fixed 851 with the Flather scheme using tidal harmonics and possibly output 852 from a large-scale model, and FRS conditions are applied to the tracers 853 and baroclinic velocity fields, using fields from a large-scale model. 854 855 Note that FRS conditions will work with the filtered 856 (\key{dynspg\_flt}) or time-split (\key{dynspg\_ts}) solutions for the 857 surface pressure gradient. The Flather condition will only work for 858 the time-split solution (\key{dynspg\_ts}). FRS conditions are applied 859 at the end of the main model time step. Flather conditions are applied 860 during the barotropic subcycle in the time-split solution. 901 defined on the $T$ points with $nbr=1$ and $\eta$ is defined on the 902 $T$ points with $nbr=2$. $U$ and $U_{e}$ are defined on the $U$ or 903 $V$ points with $nbr=1$, $i.e.$ between the two $T$ grid points. 861 904 862 905 %---------------------------------------------- … … 864 907 \label{BDY_geometry} 865 908 866 The definition of the open boundary is completely flexible. An example 867 is shown in Fig.~\ref{Fig_LBC_bdy_geom}. The boundary zone is 868 defined by a series of index arrays read in from the input boundary 869 data files: $nbidta$, $nbjdta$, and $nbrdta$. The first two of these 870 define the global $(i,j)$ indices of each point in the boundary zone 871 and the $nbrdta$ array defines the discrete distance from the boundary 872 with $nbrdta=1$ meaning that the point is next to the edge of the 873 model domain and $nbrdta>1$ showing that the point is increasingly 874 further away from the edge of the model domain. These arrays are 875 defined separately for each of the $T$, $U$ and $V$ grids, but the 876 relationship between the points is assumed to be as in Fig. 877 \ref{Fig_LBC_bdy_geom} with the $T$ points forming the outermost row 878 of the boundary and the first row of velocities normal to the boundary 879 being inside the first row of $T$ points. The order in which the 880 points are defined is unimportant. 909 Each open boundary set is defined as a list of points. The information 910 is stored in the arrays $nbi$, $nbj$, and $nbr$ in the $idx\_bdy$ 911 structure. The $nbi$ and $nbj$ arrays 912 define the local $(i,j)$ indices of each point in the boundary zone 913 and the $nbr$ array defines the discrete distance from the boundary 914 with $nbr=1$ meaning that the point is next to the edge of the 915 model domain and $nbr>1$ showing that the point is increasingly 916 further away from the edge of the model domain. A set of $nbi$, $nbj$, 917 and $nbr$ arrays is defined for each of the $T$, $U$ and $V$ 918 grids. Figure \ref{Fig_LBC_bdy_geom} shows an example of an irregular 919 boundary. 920 921 The boundary geometry for each set may be defined in a namelist 922 nambdy\_index or by reading in a ``coordinates.bdy.nc'' file. The 923 nambdy\_index namelist defines a series of straight-line segments for 924 north, east, south and west boundaries. For the northern boundary, 925 \np{nbdysegn} gives the number of segments, \np{jpjnob} gives the $j$ 926 index for each segment and \np{jpindt} and \np{jpinft} give the start 927 and end $i$ indices for each segment with similar for the other 928 boundaries. These segments define a list of $T$ grid points along the 929 outermost row of the boundary ($nbr\,=\, 1$). The code deduces the $U$ and 930 $V$ points and also the points for $nbr\,>\, 1$ if 931 $nn\_rimwidth\,>\,1$. 932 933 The boundary geometry may also be defined from a 934 ``coordinates.bdy.nc'' file. Figure \ref{Fig_LBC_nc_header} 935 gives an example of the header information from such a file. The file 936 should contain the index arrays for each of the $T$, $U$ and $V$ 937 grids. The arrays must be in order of increasing $nbr$. Note that the 938 $nbi$, $nbj$ values in the file are global values and are converted to 939 local values in the code. Typically this file will be used to generate 940 external boundary data via interpolation and so will also contain the 941 latitudes and longitudes of each point as shown. However, this is not 942 necessary to run the model. 943 944 For some choices of irregular boundary the model domain may contain 945 areas of ocean which are not part of the computational domain. For 946 example if an open boundary is defined along an isobath, say at the 947 shelf break, then the areas of ocean outside of this boundary will 948 need to be masked out. This can be done by reading a mask file defined 949 as \np{cn\_mask\_file} in the nam\_bdy namelist. Only one mask file is 950 used even if multiple boundary sets are defined. 881 951 882 952 %>>>>>>>>>>>>>>>>>>>>>>>>>>>> … … 892 962 \label{BDY_data} 893 963 894 The input data files for the FRS conditions are defined in the 895 namelist as \np{cn\_dta\_frs\_T}, \np{cn\_dta\_frs\_U}, 896 \np{cn\_dta\_frs\_V}. The input data files for the Flather conditions 897 are defined in the namelist as \np{cn\_dta\_fla\_T}, 898 \np{cn\_dta\_fla\_U}, \np{cn\_dta\_fla\_V}. 899 900 The netcdf header of a typical input data file is shown in Fig.~\ref{Fig_LBC_nc_header}. 901 The file contains the index arrays which define the boundary geometry 902 as noted above and the data arrays for each field. 903 The data arrays are dimensioned on: a time dimension; $xb$ 904 which is the index of the boundary data point in the horizontal; 905 and $yb$ which is a degenerate dimension of 1 to enable 906 the file to be read by the standard NEMO I/O routines. The 3D fields 907 also have a depth dimension. 908 909 If \np{ln\_clim} is set to \textit{false}, the model expects the 910 units of the time axis to have the form shown in 911 Fig.~\ref{Fig_LBC_nc_header}, $i.e.$ {\it ``seconds since yyyy-mm-dd 912 hh:mm:ss''} The fields are then linearly interpolated to the model 913 time at each timestep. Note that for this option, the time axis of the 914 input files must completely span the time period of the model 915 integration. If \np{ln\_clim} is set to \textit{true} (climatological 916 boundary forcing), the model will expect either a single set of annual 917 mean fields (constant boundary forcing) or 12 sets of monthly mean 918 fields in the input files. 919 920 As in the OBC module there is an option to use initial conditions as 921 boundary conditions. This is chosen by setting 922 \np{nn\_dtactl}~=~0. However, since the model defines the boundary 923 geometry by reading the boundary index arrays from the input files, 924 it is still necessary to provide a set of input files in this 925 case. They need only contain the boundary index arrays, $nbidta$, 926 \textit{nbjdta}, \textit{nbrdta}. 964 The data files contain the data arrays 965 in the order in which the points are defined in the $nbi$ and $nbj$ 966 arrays. The data arrays are dimensioned on: a time dimension; 967 $xb$ which is the index of the boundary data point in the horizontal; 968 and $yb$ which is a degenerate dimension of 1 to enable the file to be 969 read by the standard NEMO I/O routines. The 3D fields also have a 970 depth dimension. 971 972 At Version 3.4 there are new restrictions on the order in which the 973 boundary points are defined (and therefore restrictions on the order 974 of the data in the file). In particular: 975 976 \mbox{} 977 978 \begin{enumerate} 979 \item The data points must be in order of increasing $nbr$, ie. all 980 the $nbr=1$ points, then all the $nbr=2$ points etc. 981 \item All the data for a particular boundary set must be in the same 982 order. (Prior to 3.4 it was possible to define barotropic data in a 983 different order to the data for tracers and baroclinic velocities). 984 \end{enumerate} 985 986 \mbox{} 987 988 These restrictions mean that data files used with previous versions of 989 the model may not work with version 3.4. A fortran utility 990 {\it bdy\_reorder} exists in the TOOLS directory which will re-order the 991 data in old BDY data files. 927 992 928 993 %>>>>>>>>>>>>>>>>>>>>>>>>>>>> … … 930 995 \includegraphics[width=1.0\textwidth]{./TexFiles/Figures/Fig_LBC_nc_header.pdf} 931 996 \caption { \label{Fig_LBC_nc_header} 932 Example of header of netcdf input data file for BDY}997 Example of the header for a coordinates.bdy.nc file} 933 998 \end{center} \end{figure} 934 999 %>>>>>>>>>>>>>>>>>>>>>>>>>>>> … … 940 1005 There is an option to force the total volume in the regional model to be constant, 941 1006 similar to the option in the OBC module. This is controlled by the \np{nn\_volctl} 942 parameter in the namelist. A value of \np{nn\_volctl}~=~0 indicates that this option is not used.1007 parameter in the namelist. A value of \np{nn\_volctl}~=~0 indicates that this option is not used. 943 1008 If \np{nn\_volctl}~=~1 then a correction is applied to the normal velocities 944 1009 around the boundary at each timestep to ensure that the integrated volume flow … … 947 1012 flux across the surface and the correction velocity corrects for this as well. 948 1013 949 1014 If more than one boundary set is used then volume correction is 1015 applied to all boundaries at once. 1016 1017 \newpage 950 1018 %---------------------------------------------- 951 1019 \subsection{Tidal harmonic forcing} 952 1020 \label{BDY_tides} 953 1021 1022 %-----------------------------------------nambdy_tide-------------------------------------------- 1023 \namdisplay{nambdy_tide} 1024 %----------------------------------------------------------------------------------------------- 1025 954 1026 To be written.... 955 1027
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