Changes

Updating the code to set the bottom of the thermodynamic level grid for
diffusion at thermodynamic level 2 -- the first level above the surface.

This is being done in preparation for ghostless gridding.

Commit to enforce a fixed-point boundary condition of wp3=0 at
thermodynamic level k = 2, the first above-ground thermodynamic level.

This is being done in preparation for ghostless gridding.

This commit is BIT_CHANGING.

Results are much more similar to the previous results than using
using zero-flux as the lower boundary condition for wp3.