  with respect to temperature in lowest model layer.
                     Units = W/(m**2 K)

                devap_datmos = derivative of surface flux of water vapor 
                     with respect to specific humidity in lowest model layer.
                     Units = kg/(m**2 s)

    
    input/output:

         sens, evap, tau_u, tau_v -- real, dimension(:,:)
             Surface fluxes (positive upwards) 
             shape must conform to first two dimensions of input fields

             Units:  