ospheric fields 
                     from time i   for two-time level schemes
                     from time i-1 for leapgrog

             If dflux_datmos is non-zero, input flux is modified by 
             the implicit correction to be 
                 flux(i+1) = flux(i or i-1) + delt*dflux_datmos*dt_xi(:,:,N)
                 where dt_xi is the final (output) tendency and 
                 N is the lowest model level

         flux_tr -- real, dimension(:,:,:) 
                   with size(flux,tr_3)