 Pascals


             Flux should be evaluated at time i   for two-time level schemes
                                   and at time i-1 for leapgrog
             If dtau_datmos is non-zero, input stress is modified by 
             the implicit correction 
                 tau_u(i+1) = tau_u(i or i-1) + delt*dtau_datmos*dt_u(:,:,N)
                 where dt_u is the final (output) tendency and 
                 N is the lowest model level; similarly for tau_v

         flux_tr -- real, dimension(:,:,:) 
