Difference between revisions of "Baroclinic vs. barotropic mode"
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Some description of the Baroclinic and Barotropic equations is given in the SELFE paper. A little elaboration will convey how these are implemented and used in practice. | Some description of the Baroclinic and Barotropic equations is given in the SELFE paper. A little elaboration will convey how these are implemented and used in practice. | ||
| − | The | + | The baroclinic and barotropic modes are toggled in the model by means of the parameter ***. They differ in that in Baroclinic mode, the contribution of salinity-induced density differences is included in the momentum equations. In contrast, in Barotropic mode salt and temperature are (at most) considered passive tracers. |
In barotropic mode: | In barotropic mode: | ||
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== Performance considerations == | == Performance considerations == | ||
| − | Barotropic mode calculation can be a lot faster than | + | Barotropic mode calculation can be a lot faster than baroclinic. A key speedup is achieved by setting ''itracer=0'' and neglecting salt and temperature entirely, which is particularly common in the case that subcycling of transport is a performance limiter. |
Revision as of 12:08, 27 August 2012
Contents
Mode descriptions
Some description of the Baroclinic and Barotropic equations is given in the SELFE paper. A little elaboration will convey how these are implemented and used in practice.
The baroclinic and barotropic modes are toggled in the model by means of the parameter ***. They differ in that in Baroclinic mode, the contribution of salinity-induced density differences is included in the momentum equations. In contrast, in Barotropic mode salt and temperature are (at most) considered passive tracers.
In barotropic mode:
- You can choose whether to calculate salt and temperature transport by toggling the itracer parameter in the param.in file.
- This choice affects performance (see below) and also data requirements for salt and temperature. The model (****is/isn't smart) about ...
- The contribution of density to horizontal pressure gradients is dropped.
- The turbulence closure is still calculated in 3D, but the supression of turbulence due to stratification is not included.
Performance considerations
Barotropic mode calculation can be a lot faster than baroclinic. A key speedup is achieved by setting itracer=0 and neglecting salt and temperature entirely, which is particularly common in the case that subcycling of transport is a performance limiter.
Boundary and well-posedness issues
Sequential barotropic-baroclinic analysis
One common usage pattern is to use a sequence of barotropic-baroclinic model runs. The barotropic simulation is used in a preliminary sweep in order to calculate 3D boundary conditions for the subsequent baroclinic analysis. Typically this is done with transport off, maximizing speed for the barotropic step.
