33.1.2.1 The standard Cox 1984 scheme: oldconvect

Since the GFDL model works the grid row by row, we'll only discuss how one grid-row is treated. Here's how:

1.

Compute the densities for all grid cells in the row. Two adjacent levels are always referenced to the same pressure in order to get the static stability of this pair of levels.

2.

Mix all unstable pairs.

3.

Since we have now only compared and mixed ``even'' pairs (i.e. levels 1 & 2; levels 3 & 4; etc), repeat steps (1) and (2) for ``odd'' pairs (i.e. levels 2 & 3; levels 4 & 5; etc).

4.

Repeat steps (1)-(3) a predetermined number of times.

There are a couple of problems here. We've already said that strictly speaking this never leads to complete mixing of an unstable water column. So the process is repeated several times at each time step to approximate complete mixing. But each time all grid cells are checked for instabilities again, even those we already found to be stable. Each density calculation requires evaluation of a third order polynomial (Cox 1972) in T and S. This is where the cpu time is eaten up.