          (defined in gcm_vert_diff_down -- not used elsewhere)

     dflux_t = derivative of the temperature flux at the top of the lowest
               atmospheric layer with respect to the temperature
               of that layer  (J/(m2 K))
               (defined in gcm_vert_diff_down -- not used elsewhere)

     dflux_q = derivative of the flux of specific humidity 
               at the top of the lowest atmospheric layer with respect to 
               the specific humidity of that layer  (--/(m2 K