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\subsection{OBCS: Open boundary conditions for regional modeling} |
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|
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\label{sec:pkg:obcs} |
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\begin{rawhtml} |
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<!-- CMIREDIR:package_obcs: --> |
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\end{rawhtml} |
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|
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Authors: |
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Alistair Adcroft, Patrick Heimbach, Samar Katiwala, Martin Losch |
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|
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\subsubsection{Introduction |
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\label{sec:pkg:obcs:intro}} |
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|
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|
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%---------------------------------------------------------------------- |
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|
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\subsubsection{OBCS configuration and compiling |
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\label{sec:pkg:kpp:comp}} |
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|
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As with all MITgcm packages, OBCS can be turned on or off |
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at compile time |
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% |
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\begin{itemize} |
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% |
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\item |
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using the \texttt{packages.conf} file by adding \texttt{obcs} to it, |
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% |
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\item |
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or using \texttt{genmake2} adding |
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\texttt{-enable=obcs} or \texttt{-disable=obcs} switches |
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% |
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\item |
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\textit{Required packages and CPP options:} \\ |
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% |
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To alternatives are available for prescribing open boundary values, |
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which differ in the way how OB's are treated in time: |
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A simple time-management (e.g. constant in time, or cyclic with |
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fixed fequency) is provided through |
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S/R \texttt{obcs\_external\_fields\_load}. |
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More sophisticated ``real-time'' (i.e. calendar time) management is |
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available through \texttt{obcs\_prescribe\_read}. |
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The latter case requires |
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packages \texttt{cal} and \texttt{exf} to be enabled. |
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% |
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\end{itemize} |
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(see also Section \ref{sect:buildingCode}). |
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|
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Parts of the OBCS code can be enabled or disabled at compile time |
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via CPP preprocessor flags. These options are set in |
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\texttt{OBCS\_OPTIONS.h}. Table \ref{tab:pkg:obcs:cpp} summarizes them. |
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|
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\begin{table}[h!] |
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\centering |
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\label{tab:pkg:obcs:cpp} |
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{\footnotesize |
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\begin{tabular}{|l|l|} |
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\hline |
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\textbf{CPP option} & \textbf{Description} \\ |
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\hline \hline |
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\texttt{ALLOW\_OBCS\_NORTH} & |
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enable Northern OB \\ |
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\texttt{ALLOW\_OBCS\_SOUTH} & |
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enable Southern OB \\ |
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\texttt{ALLOW\_OBCS\_EAST} & |
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enable Eastern OB \\ |
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\texttt{ALLOW\_OBCS\_WEST} & |
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enable Western OB \\ |
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\hline |
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\texttt{ALLOW\_OBCS\_PRESCRIBE} & |
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enable code for prescribing OB's \\ |
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\texttt{ALLOW\_OBCS\_SPONGE} & |
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enable sponge layer code \\ |
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\texttt{ALLOW\_OBCS\_BALANCE} & |
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enable code for balancing transports through OB's \\ |
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\texttt{ALLOW\_ORLANSKI} & |
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enable Orlanski radiation conditions at OB's \\ |
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\hline |
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\end{tabular} |
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} |
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\caption{~} |
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\end{table} |
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|
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|
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%---------------------------------------------------------------------- |
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|
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\subsubsection{Run-time parameters |
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\label{sec:pkg:obcs:runtime}} |
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|
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Run-time parameters are set in files |
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\texttt{data.pkg}, \texttt{data.obcs}, and \texttt{data.exf} |
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if ``real-time'' prescription is requested |
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(i.e. package \texttt{exf} enabled). |
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These parameter files are read in S/R |
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\texttt{packages\_readparms.F}, \texttt{obcs\_readparms.F}, and |
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\texttt{exf\_readparms.F}, respectively. |
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Run-time parameters may be broken into 3 categories: |
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(i) switching on/off the package at runtime, |
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(ii) OBCS package flags and parameters, |
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(iii) additional timing flags in \texttt{data.exf}, if selected. |
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|
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\paragraph{Enabling the package} |
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~ \\ |
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% |
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The OBCS package is switched on at runtime by setting |
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\texttt{useOBCS = .TRUE.} in \texttt{data.pkg}. |
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|
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\paragraph{Package flags and parameters} |
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~ \\ |
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% |
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Table \ref{tab:pkg:obcs:runtime_flags} summarizes the |
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runtime flags that are set in \texttt{data.obcs}, and |
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their default values. |
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|
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\begin{table}[h!] |
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\centering |
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\label{tab:pkg:obcs:runtime_flags} |
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{\footnotesize |
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\begin{tabular}{|l|c|l|} |
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\hline |
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\textbf{Flag/parameter} & \textbf{default} & \textbf{Description} \\ |
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\hline \hline |
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\multicolumn{3}{|c|}{\textit{basic flags \& parameters} } \\ |
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\hline |
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OB\_Jnorth & 0 & |
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Nx-vector of J-indices (w.r.t. Ny) of Northern OB |
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at each I-position (w.r.t. Nx) \\ |
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OB\_Jsouth & 0 & |
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Nx-vector of J-indices (w.r.t. Ny) of Southern OB |
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at each I-position (w.r.t. Nx) \\ |
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OB\_Ieast & 0 & |
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Ny-vector of I-indices (w.r.t. Nx) of Eastern OB |
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at each J-position (w.r.t. Ny) \\ |
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OB\_Iwest & 0 & |
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Ny-vector of I-indices (w.r.t. Nx) of Western OB |
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at each J-position (w.r.t. Ny) \\ |
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useOBCSprescribe & \texttt{.FALSE.} & |
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~ \\ |
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useOBCSsponge & \texttt{.FALSE.} & |
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~ \\ |
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useOBCSbalance & \texttt{.FALSE.} & |
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~ \\ |
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OB\textbf{X}\textbf{y}File & ~ & |
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file name of OB field \\ |
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~ & ~ & |
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\textbf{X}: \textbf{N}(orth), \textbf{S}(outh), |
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\textbf{E}(ast), \textbf{W}(est) \\ |
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~ & ~ & |
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\textbf{y}: \textbf{t}(emperature), \textbf{s}(salinity), |
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\textbf{u}(-velocity), \textbf{v}(-velocity) \\ |
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\hline |
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\multicolumn{3}{|c|}{\textit{Orlanski parameters} } \\ |
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\hline |
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cvelTimeScale & 2000 sec & |
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averaging period for phase speed \\ |
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CMAX & 0.45 m/s & |
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maximum allowable phase speed-CFL for AB-II \\ |
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CFIX & 0.8 m/s & |
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fixed boundary phase speed \\ |
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useFixedCEast & .FALSE. & |
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~ \\ |
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useFixedCWest & .FALSE. & |
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~ \\ |
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\hline |
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\multicolumn{3}{|c|}{\textit{Sponge-layer parameters} } \\ |
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\hline |
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spongeThickness & 0 & |
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sponge layer thickness (in \# grid points) \\ |
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Urelaxobcsinner & 0 sec & |
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relaxation time scale at the |
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innermost sponge layer point of a meridional OB \\ |
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Vrelaxobcsinner & 0 sec & |
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relaxation time scale at the |
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innermost sponge layer point of a zonal OB \\ |
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Urelaxobcsbound & 0 sec & |
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relaxation time scale at the |
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outermost sponge layer point of a meridional OB \\ |
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Vrelaxobcsbound & 0 sec & |
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relaxation time scale at the |
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outermost sponge layer point of a zonal OB \\ |
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\hline |
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\hline |
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\end{tabular} |
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} |
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\caption{~} |
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\end{table} |
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|
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%---------------------------------------------------------------------- |
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|
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\subsubsection{Defining open boundary positions |
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\label{sec:pkg:obcs:defining}} |
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|
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There are four open boundaries (OBs), a |
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Northern, Southern, Eastern, and Western. |
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All OB locations are specified by their absolute |
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meridional (Northern/Southern) or zonal (Eastern/Western) indices. |
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Thus, for each zonal position $i=1,\ldots,Nx$ a meridional index |
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$j$ specifies the Northern/Southern OB position, |
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and for each meridional position $j=1,\ldots,Ny$, a zonal index |
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$i$ specifies the Eastern/Western OB position. |
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For Northern/Southern OB this defines an $Nx$-dimensional |
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``row'' array $\tt OB\_Jnorth(Ny)$ / $\tt OB\_Jsouth(Ny)$, |
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and an $Ny$-dimenisonal |
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``column'' array $\tt OB\_Ieast(Nx)$ / $\tt OB\_Iwest(Nx)$ |
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Positions determined in this way allows Northern/Southern |
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OBs to be at variable $j$ (or $y$) positions, and Eastern/Western |
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OBs at variable $i$ (or $x$) positions. |
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Here, indices refer to tracer points on the C-grid. |
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A zero (0) element in $\tt OB\_I\ldots$, $\tt OB\_J\ldots$ |
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means there is no corresponding OB in that column/row. |
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For a Northern/Southern OB, the OB V point is to the South/North. |
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For an Eastern/Western OB, the OB U point is to the West/East. |
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|
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\begin{verbatim} |
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For example |
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OB_Jnorth(3)=34 means that: |
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T( 3 ,34) is a an OB point |
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U(3:4,34) is a an OB point |
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V( 4 ,34) is a an OB point |
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while |
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OB_Jsouth(3)=1 means that: |
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T( 3 ,1) is a an OB point |
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U(3:4,1) is a an OB point |
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V( 4 ,2) is a an OB point |
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\end{verbatim} |
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|
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For convenience, negative values for Jnorth/Ieast refer to |
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points relative to the Northern/Eastern edges of the model |
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eg. $\tt OB\_Jnorth(3)=-1$ means that the point $\tt (3,Ny)$ |
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is a northern OB. |
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|
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\noindent |
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\textsf{Add special comments for case \#define NONLIN\_FRSURF, |
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see obcs\_ini\_fixed.F} |
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|
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%---------------------------------------------------------------------- |
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|
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\subsubsection{Equations and key routines |
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\label{sec:pkg:obcs:equations}} |
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|
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\paragraph{OBCS\_READPARMS:} ~ \\ |
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Set OB positions through arrays |
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{\tt OB\_Jnorth(Ny), OB\_Jsouth(Ny), OB\_Ieast(Nx), OB\_Iwest(Nx)}, |
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and runtime flags see Table \ref{tab:???}. |
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|
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\paragraph{OBCS\_CALC:} ~ \\ |
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% |
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Top-level routine for filling values to be applied at OB for |
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$T,S,U,V,\eta$ into corresponding |
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``slice'' arrays $(x,z)$, $(y,z)$ for each OB: |
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$\tt OB[N/S/E/W][t/s/u/v]$; e.g. for salinity array at |
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Southern OB, array name is $\tt OBSt$. |
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Values filled are either |
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% |
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\begin{itemize} |
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% |
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\item |
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constant vertical $T,S$ profiles as specified in file |
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{\tt data} ({\tt tRef(Nr), sRef(Nr)}) with zero velocities $U,V$, |
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% |
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\item |
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$T,S,U,V$ values determined via Orlanski radiation conditions |
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(see below), |
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% |
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\item |
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prescribed time-constant or time-varying fields (see below). |
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% |
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\end{itemize} |
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|
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|
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\paragraph{ORLANSKI} ~ \\ |
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% |
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Orlanski radiation conditions |
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|
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\paragraph{OBCS\_PRESCRIBE\_READ} Setting OB fields and updates \\ |
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% |
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~ |
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|
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\paragraph{OBCS\_BALANCE} ~ \\ |
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% |
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~ |
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|
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\paragraph{OBCS\_APPLY\_*:} ~ \\ |
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~ |
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|
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\paragraph{OBCS\_SPONGE} Setting sponge layer characteristics \\ |
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% |
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~ |
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|
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\paragraph{OB's with nonlinear free surface} ~ \\ |
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% |
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~ |
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|
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|
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%---------------------------------------------------------------------- |
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|
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\subsubsection{Flow chart |
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\label{sec:pkg:obcs:flowchart}} |
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|
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|
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{\footnotesize |
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\begin{verbatim} |
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|
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C !CALLING SEQUENCE: |
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c ... |
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|
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\end{verbatim} |
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} |
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|
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%---------------------------------------------------------------------- |
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|
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\subsubsection{OBCS diagnostics |
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\label{sec:pkg:obcs:diagnostics}} |
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|
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Diagnostics output is available via the diagnostics package |
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(see Section \ref{sec:pkg:diagnostics}). |
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Available output fields are summarized in |
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Table \ref{tab:pkg:obcs:diagnostics}. |
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|
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\begin{table}[h!] |
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\centering |
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\label{tab:pkg:obcs:diagnostics} |
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{\footnotesize |
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\begin{verbatim} |
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------------------------------------------------------ |
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<-Name->|Levs|grid|<-- Units -->|<- Tile (max=80c) |
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------------------------------------------------------ |
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|
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\end{verbatim} |
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} |
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\caption{~} |
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\end{table} |
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|
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%---------------------------------------------------------------------- |
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|
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\subsubsection{Reference experiments} |
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|
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|
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|
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%---------------------------------------------------------------------- |
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|
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\subsubsection{References} |
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