/[MITgcm]/manual/s_phys_pkgs/text/obcs.tex

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-revision 1.6 by mlosch,
Fri Feb 25 17:26:17 2011 UTC
+revision 1.9 by mlosch,
Thu Mar  3 07:46:09 2011 UTC
 Line 11 
 Alistair Adcroft, Patrick Heimbach, Sama
  \subsubsection{Introduction
  \label{sec:pkg:obcs:intro}}
+ The OBCS-package is fundamental to regional ocean modelling with the
+ MITgcm, but there are so many details to be considered in
+ regional ocean modelling that this package cannot accomodate all
+ imaginable and possible options. Therefore, for a regional simulation
+ with very particular details, it is recommended to familiarize oneself
+ not only with the compile- and runtime-options of this package, but
+ also with the code itself. In many cases it will be necessary to adapt
+ the obcs-code (in particular \code{S/R OBCS\_CALC}) to the application
+ in question; in these cases the obcs-package (together with the
+ rbcs-package, section \ref{sec:pkg:rbcs}) is a very
+ useful infrastructure for implementing special regional models.
  %----------------------------------------------------------------------
-Line 95 
 Run-time parameters are set in files
+Line 105 
 Run-time parameters are set in files
  \code{data.pkg}, \code{data.obcs}, and \code{data.exf}
  if ``real-time'' prescription is requested
  (i.e. package \code{exf} enabled).
- These parameter files are read in S/R
+ vThese parameter files are read in S/R
  \code{packages\_readparms.F}, \code{obcs\_readparms.F}, and
  \code{exf\_readparms.F}, respectively.
  Run-time parameters may be broken into 3 categories:
-Line 143 
 their default values.
+Line 153 
 their default values.
             ~ \\
          useOBCSbalance & \code{.FALSE.} &
             ~ \\
+            OBCS\_balanceFacN/S/E/W & 0 & factor(s) determining the details
+            of the balaning code \\
          useOrlanskiNorth/South/EastWest & \code{.FALSE.} &
             turn on Orlanski boundary conditions for individual boundary\\
          useStevensNorth/South/EastWest & \code{.FALSE.} &
-Line 232 
 A zero (0) element in $\tt OB\_I\ldots$,
+Line 244 
 A zero (0) element in $\tt OB\_I\ldots$,
  means there is no corresponding OB in that column/row.
  For a Northern/Southern OB, the OB V point is to the South/North.
  For an Eastern/Western OB, the OB U point is to the West/East.
+ For example,
- \begin{verbatim}
+ \begin{tabbing}
-  For example
+   \code{OB\_Jnorth(3)=34} \=  means that:  \= \\
-      OB_Jnorth(3)=34  means that:
+   \> \code{T(3,34)} \> is a an OB point  \\
-           T( 3 ,34) is a an OB point
+   \> \code{U(3,34)} \> is a an OB point \\
-           U(3:4,34) is a an OB point
+   \> \code{V(3,34)} \> is a an OB point \\
-           V( 4 ,34) is a an OB point
+   \code{OB\_Jsouth(3)=1} \> means that: \\
-  while
+   \> \code{T(3,1)} \> is a an OB point \\
-      OB_Jsouth(3)=1  means that:
+   \> \code{U(3,1)} \> is a an OB point \\
-           T( 3 ,1) is a an OB point
+   \> \code{V(3,2)} \> is a an OB point \\
-           U(3:4,1) is a an OB point
+   \code{OB\_Ieast(10)=69} \>  means that:  \>  \\
-           V( 4 ,2) is a an OB point
+   \> \code{T(69,10)} \> is a an OB point \\
- \end{verbatim}
+   \> \code{U(69,10)} \> is a an OB point \\
+   \> \code{V(69,10)} \> is a an OB point \\
- For convenience, negative values for Jnorth/Ieast refer to
+   \code{OB\_Iwest(10)=1} \>  means that:  \>  \\
+   \> \code{T(1,10)} \> is a an OB point \\
+   \> \code{U(2,10)} \> is a an OB point \\
+   \> \code{V(1,10)} \> is a an OB point
+ \end{tabbing}
+ For convenience, negative values for \code{Jnorth}/\code{Ieast} refer to
  points relative to the Northern/Eastern edges of the model
  eg. $\tt OB\_Jnorth(3)=-1$  means that the point $\tt (3,Ny)$
  is a northern OB.
-Line 291 
 prescribed time-constant or time-varying
+Line 308 
 prescribed time-constant or time-varying
  use prescribed boundary fields to compute Stevens boundary conditions.
  \end{itemize}
  \paragraph{ORLANSKI:} ~ \\
  %
  Orlanski radiation conditions \citep{orl:76}, examples can be found in
-Line 317 
 open boundary:
+Line 333 
 open boundary:
  \item If non-hydrostatic dynamics are used
    (\ref{sec:non-hydrostatic}), additional files
    \code{OB[N/S/E/W]wFile} for the vertical velocity $w$ with
-   dimensions $(N_{x/y}\times N_r\times\mbox{time levels})$ may be
+   dimensions $(N_{x/y}\times N_r\times\mbox{time levels})$ can be
    specified.
  \item If \code{useSEAICE=.TRUE.} then additional files
    \code{OB[N/S/E/W][a,h,sl,sn,uice,vice]} for sea ice area, thickness
    (\code{HEFF}), seaice salinity, snow and ice velocities
-   $(N_{x/y}\times\mbox{time levels})$ may be specified.
+   $(N_{x/y}\times\mbox{time levels})$ can be specified.
  \end{itemize}
- When the \code{exf}-package is used, the time levels are controlled
+ As in \code{S/R external\_fields\_load} or the \code{exf}-package, the
- for each boundary separately in the same way as the \code{exf}-fields
+ code reads two time levels for each variable, e.g.\ \code{OBNu0} and
- in \code{data.exf}, namelist \code{EXF\_NML\_OBCS}. The runtime flags
+ \code{OBNu1}, and interpolates linearly between these time levels to
+ obtain the value \code{OBNu} at the current model time (step). When the
+ \code{exf}-package is used, the time levels are controlled for each
+ boundary separately in the same way as the \code{exf}-fields in
+ \code{data.exf}, namelist \code{EXF\_NML\_OBCS}. The runtime flags
  follow the above naming conventions, e.g. for the western boundary the
  corresponding flags are \code{OBCWstartdate1/2} and
  \code{OBCWperiod}. Sea-ice boundary values are controlled separately
- with \code{siobWstartdate1/2} and \code{siobWperiod}.
+ with \code{siobWstartdate1/2} and \code{siobWperiod}.  When the
- When the \code{exf}-package is not used, the time levels are
+ \code{exf}-package is not used, the time levels are controlled by the
- controlled by the runtime flags \code{externForcingPeriod} and
+ runtime flags \code{externForcingPeriod} and \code{externForcingCycle}
- \code{externForcingCycle} in \code{data}, see \code{verification/exp4}
+ in \code{data}, see \code{verification/exp4} for an example.
- for an example.
  \paragraph{OBCS\_CALC\_STEVENS:} ~ \\
  (THE IMPLEMENTATION OF THESE BOUNDARY CONDITIONS IS NOT COMPLETE. SO
-Line 367 
 example, we use the notation for an east
+Line 386 
 example, we use the notation for an east
    \texttt{useStevensPhaseVel} and \texttt{useStevensAdvection} to
    \texttt{.FALSE.}.\end{itemize} See \citet{stevens:90} for details.
- \paragraph{OBCS\_BALANCE} ~ \\
+ \paragraph{OBCS\_BALANCE:} ~ \\
  %
- ~
+ This is not (yet) a separate routine in the code, but it may become
+ one to make this code more transparent. The code is part of
+ \code{S/R~OBCS\_CALC}. When turned on (\code{ALLOW\_OBCS\_BALANCE}
+ defined in \code{OBCS\_OPTIONS.h} and \code{useOBCSbalance=.true.} in
+ \code{data.obcs/OBCS\_PARM01}), the normal velocities across each of
+ the four boundaries are modified separately, so that the net volume
+ transport across \emph{each} boundary is zero. For example, for the
+ western boundary at $i=i_{b}$, the modified velocity is:
+ \[
+ u(y,z) - \int_{\mbox{western boundary}}u\,dy\,dz \approx OBNu(j,k) - \sum_{j,k}
+ OBNu(j,k) h_{w}(i_{b},j,k)\Delta{y_G(i_{b},j)}\Delta{z(k)}.
+ \]
+ This also ensures a net total inflow of zero through all boundaries to
+ make it a useful flag to prevent infinite sea-level change within the
+ domain, but the flag is \emph{not} useful if you want to simulate,
+ say, a sector of the Southern Ocean with a strong ACC entering through
+ the western and leaving through the eastern boundary, because this
+ flag will make sure that the strong inflow is removed. It is
+ recommended that this part of the code is adapted to the particular
+ needs of the simulation in question.
  \paragraph{OBCS\_APPLY\_*:} ~ \\
  ~
-Line 425 
 Table \ref{tab:pkg:obcs:diagnostics}.
+Line 463 
 Table \ref{tab:pkg:obcs:diagnostics}.
  %----------------------------------------------------------------------
  \subsubsection{Reference experiments}
+ In the directory \code{verifcation}, the following experiments use
+ \code{obcs}:
+ \begin{itemize}
+ \item \code{exp4}: box with 4 open boundaries, simulating flow over a
+   Gaussian bump based on \citet{adcroft:97}, also tests
+   Stevens-boundary conditions;
+ \item \code{dome}: based on the project ``Dynamics of Overflow Mixing
+   and Entrainment''
+   (\url{http://www.rsmas.miami.edu/personal/tamay/DOME/dome.html}), uses
+   Orlanski-BCs;
+ \item \code{internal\_wave}: uses a heavily modified \code{S/R~OBCS\_CALC}
+ \item \code{seaice\_obcs}: simple example who to use the sea-ice
+   related code, based on \code{lab\_sea};
+ \item \code{tutorial\_plume\_on\_slope}: uses Orlanski-BCs, see also
+   section~\ref{sec:eg-gravityplume}.
+ \end{itemize}
-Line 436 
 Table \ref{tab:pkg:obcs:diagnostics}.
+Line 490 
 Table \ref{tab:pkg:obcs:diagnostics}.
  \label{sec:pkg:obcs:experiments}
  \begin{itemize}
- \item{Ocean experiment in exp4 verification directory. }
+ \item \code{tutorial\_plume\_on\_slope} (section~\ref{sec:eg-gravityplume})
  \end{itemize}

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