Up to now the same time step must be used in both the coarse and the fine models. In a near future we should be able to increase the time step in the coarse model, so reducing the computation load for this model.

The integration of the equations in the two models is done as following for each variable :

- Computation of the time step in the coarse model
- Extraction of the values situated along the boundaries of the nested area from the coarse model
- Interpolation of those values along the boundaries so that we have one boundary condition per point for the fine model
- Replacement of the interpolated values at the boundaries of the fine model
- Computation of the time step in the fine model
- Averaging of the values in the fine cells covering each coarse cell on the whole nested area
- Replacement of those averaged values in the corresponding area of thecoarse model
- Next variable

There is however one difference for the barotropic part : the feed-back is done only at the end of the 2D timesteps corresponding to a 3D time step to avoid stability problems.

Wed Jun 10 10:53:44 DFT 1998