Regionally coupledUnified Model |
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Centre for Global Atmospheric Modelling
The University of Reading |
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defining the region for the regionally coupled version of HadCM3
In order to run your regionally coupled experiment you actually need to tell the UM in which region you want the coupling to be disabled. This is done prior to running the UM by creating a text file which contains information on the location of the grid-points where you want the SSTs to be prescribed. This text file contains a line for each line of latitude of the ocean model grid. Each line will contain 3 numbers, as shown below;
"latitude" "first longitude" "last longitude"
for instance, if you want to fix the SST across the Indian Ocean and Pacific between 10S and 10N, using the standard HadCM3 ocean grid then your text file should contain lines like;
...
-10.625 1 1
-9.375 30 295
-8.125 30 295
-6.875 30 295
-5.625 30 295
-4.375 30 295
...
...
9.375 30 295
10.625 1 1
...
Note that you will need an entry for each model latitude, starting at the south pole and going north. At latitudes where you want the model to be fully coupled right around the globe, enter 1 as the first and last longitude. Note that, in the above example, at all the latitudes between 10S and 10N, the 2 longitudes specified are actually over land. This ensures that all the sea-points between the first and last longitude are included. You could be more precise and specify just the relevant sea-points for each latitude, but, by choosing end points over land, no sea points will get missed by mistake.
The regional coupling system has been designed so that there is a taper zone at the north and south of the region. Within this zone the relaxation towards the specified SST becomes weaker until, outside the region the SST is fully coupled. This taper zone is designed to be 4 rows wide. You should include these rows in your specification of the region. In the above example, at latitudes between 5S and 5N, the SST will be fully specified. Polewards of 10S and 10N the SST will be fully predicted by the model. Between 5N and 10N, and 5S and 10S the SST will be a blend between the two.
Up to now, the regional coupling system has only been used to fix the SST across a whole ocean basin, so there is currently no tapering available at the east and west of the specified region. This should be fairly simple to include if you do want to fix the SSTs in say just the eastern Pacific.
Click the relax SSTs link on the left hand side for the next step.
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