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Open Boundaries Implementation in MITgcmUV |
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These are some quick explanatory notes regards implementation of open |
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boundaries (OB) and the example configuration found in |
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.../verification/exp4/ |
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Input and control of OBs |
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* The open boundaries code is used only if the LOGICAL parameter |
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openBondaries is .TRUE. |
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* Four 1-dimensional INTEGER arrays indicate the position of an OB: |
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OB_Jnorth, OB_Jsouth, OB_Ieast and OB_Iwest. |
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The values of OB_* indicate the absolute computational coordinate of an open |
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boundary. eg. OB_Jsouth(3)=4 |
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means that in the column I=3 there is a "southern" OB at tracer point J=4. |
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Similarly OB_Iwest(2)=1 means that |
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the tracer point (2,1) is an OB point. This structure for specifying OBs |
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assumes that there will be only one northern and southern OB per column and |
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similar in the other direction. An entry of 0 (zero) means there is now OB |
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in that column/row. |
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The reference to "tracer points" above introduces an important distinction |
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between particular boundaries due to the C-grid staggering of variables. At |
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a northern OB tracer point (i,j) the OB v-velocity point is at (i,j) while |
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at a southern OB tracer point (i,j) the OB v-velocity point is at (i,j+1). |
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This is all taken care of in the code but when specifying OB values it is |
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important to remember the physical coordinates of T,S,U and V are not the |
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same for a given computational index. |
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Changing the type of open boundary |
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The supplied code simply specifies model variables at the appropriate |
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points. The value to be specified can (and should) be determine using a |
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radiative condition. A skeleton code is supplied set_obcs.F to illustrate |
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how |
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this might be done. This is the only routine that needs to be edited. Edit |
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others at your own peril! |
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The examples |
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There are three examples in .../verification/exp4/ |
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1. A zonal channel (solid side walls) with open boundaries at either end: |
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data.channel |
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2. A zonal channel with a Gaussian bump and open boundaries at either end: |
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data.bumpchannel |
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3. An open domain (OBs on four sides) with a Gaussian bump: data.bump |
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Each data file has a corresponding topog.* file which is specified through |
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the variable bathyFile in data.* |
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The physical problem has a flow of U=25 cm/s specified at all open |
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boundaries. The details of the experiment can be found in Adcroft's thesis |
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(Imperial College) and in Adcroft, Hill and Marshall, MWR 1997. |
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The differences between the supplied data.* files also show how to turn |
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particular OBs on and off. |
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Compiling and running the examples |
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The examples supplied are the barotropic zonal flow over a Gaussian bump in |
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a channel. |
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* Header files: Copy or link SIZE.h, CPP_OPTIONS.h and CP_EEOPTIONS.h |
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from .../verification/exp4/ to .../model/inc/, .../model/inc/ and |
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.../eesupp.inc/ respectively |
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* Modified source: Copy set_obcs.F to .../model/src/ |
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Now compile the code as usual: |
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* cd bin |
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* ../tools/genmake -makefile |
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* make depend |
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* make |
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To run the code you must first choose a data file to use: |
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* cd ../verification/exp4 |
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* cp data.bump data |
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* ../../exe/mitgcmuv |
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Happy Open Boundarying! |