 = number of tracers
                   (although listed as inout, the implicit treatment of 
                    tracer fluxes is not implemented here, so the 
                    ouput tracer flux will be identical to the input flux
                                  

         dt_u, dt_v, dt_t, dt_q -- real, dimension(:,:,:)
             Tendency of u, v, t, q
             shape must conform to that of u, v etc
             input is the tendency due to all other processes
                 that have been a