             to this point in model, including effect of vertical 
               diffusive flux at top of lowest model level, presumed
               to be modified to include effects of surface fluxes 
               outside of this module, then used to start upward
               tridiagonal sweep,
               see  <A HREF="vert_diff.tech.ps">vert_diff.tech.ps</A>

     delta_q = similarly for the increment in specific humidity 
                (non-dimensional  = Kg/Kg)

 
===========================