Open Boundaries Implementation in MITgcmUV

These are some quick explanatory notes regards implementation of open
boundaries (OB) and the example configuration found in
.../verification/exp4/


Input and control of OBs

   * The open boundaries code is used only if the LOGICAL parameter
     openBondaries is .TRUE.
   * Four 1-dimensional INTEGER arrays indicate the position of an OB:
     OB_Jnorth, OB_Jsouth, OB_Ieast and OB_Iwest.

The values of OB_* indicate the absolute computational coordinate of an open
boundary. eg. OB_Jsouth(3)=4
means that in the column I=3 there is a "southern" OB at tracer point J=4.
Similarly OB_Iwest(2)=1 means that
the tracer point (2,1) is an OB point. This structure for specifying OBs
assumes that there will be only one northern and southern OB per column and
similar in the other direction. An entry of 0 (zero) means there is now OB
in that column/row.

The reference to "tracer points" above introduces an important distinction
between particular boundaries due to the C-grid staggering of variables. At
a northern OB tracer point (i,j) the OB v-velocity point is at (i,j)  while
at a southern OB tracer point (i,j) the OB v-velocity point is at (i,j+1).
This is all taken care of in the code but when specifying OB values it is
important to remember the physical coordinates of T,S,U and V are not the
same for a given computational index.


Changing the type of open boundary

The supplied code simply specifies model variables at the appropriate
points. The value to be specified can (and should) be determine using a
radiative condition. A skeleton code is supplied set_obcs.F to illustrate
how
this might be done. This is the only routine that needs to be edited. Edit
others at your own peril!


The examples

There are three examples in .../verification/exp4/

  1. A zonal channel (solid side walls) with open boundaries at either end:
     data.channel
  2. A zonal channel with a Gaussian bump and open boundaries at either end:
     data.bumpchannel
  3. An open domain (OBs on four sides) with a Gaussian bump: data.bump

Each data file has a corresponding topog.* file which is specified through
the variable bathyFile in data.*
The physical problem has a flow of U=25 cm/s specified at all open
boundaries. The details of the experiment can be found in Adcroft's thesis
(Imperial College) and in Adcroft, Hill and Marshall, MWR 1997.

The differences between the supplied data.* files also show how to turn
particular OBs on and off.

Compiling and running the examples

The examples supplied are the barotropic zonal flow over a Gaussian bump in
a channel.

   * Header files: Copy or link SIZE.h, CPP_OPTIONS.h and CP_EEOPTIONS.h
     from .../verification/exp4/code/ to .../model/inc/, .../model/inc/ and
     .../eesupp.inc/ respectively
   * Modified source: Copy set_obcs.F to .../model/src/

Now compile the code as usual:

   * cd bin
   * ../tools/genmake -makefile
   * make depend
   * make

To run the code you must first choose a data file to use:

   * cd ../verification/exp4/input
   * cp data.bump data
   * ../../exe/mitgcmuv

Happy Open Boundarying!