A vector/parallel method for a three-dimensional transport model coupled with bio-chemical terms

A so-called fractional step method is considered for the time integration of a three-dimensional transport-chemical model in shallow seas. In this method, the transport part and the chemical part are treated separately by appropriate integration techniques. This separation is motivated by the fact that the coupling in both parts is completely different: in the transport part we have coupling over the grid points (due to advection-diffusion operators), but there is no mutual coupling between the various species. In the chemical part, the species are coupled (due to reaction terms) per grid point, but here the coupling in space is absent. To solve the transport part, we use a specially constructed method of Hopscotch-type. Since the chemistry in water is usually of low activity, an explicit Runge-Kutta method can be used for integrating the chemical part. We discuss the implementational aspects of these methods for multi-vectorprocessors, and show performance results obtained on a Cray C98/4256.