Abstract. Ocean biogeochemical models are key tools for both scientific and
operational applications. Nevertheless the cost of these models is often
expensive because of the large number of biogeochemical tracers. This
has motivated the development of multi-grid approaches where ocean
dynamics and tracer transport are computed on grids of different spatial
resolution. However, existing multi-grid approaches to tracer transport
in ocean modelling do not allow the computation of ocean dynamics and tracer
transport simultaneously. This paper describes a new multi-grid approach
developed for accelerating the computation of passive tracer transport
in the Nucleus for European Modelling of the Ocean (NEMO) ocean circulation model. In practice, passive tracer transport
is computed at runtime on a grid with coarser spatial resolution than the
hydrodynamics, which reduces the CPU cost of computing the evolution of tracers.
We describe the multi-grid algorithm, its practical implementation in the NEMO ocean model, and
discuss its performance on the basis of a series of sensitivity
experiments with global ocean model configurations.
Our experiments confirm that the spatial resolution of hydrodynamical fields can be
coarsened by a factor of 3 in both horizontal directions without significantly affecting the resolved
passive tracer fields. Overall, the proposed algorithm yields a reduction
by a factor of 7 of the overhead associated with running a full biogeochemical
model like PISCES (with 24 passive tracers).
Propositions for further reducing this cost without affecting the
resolved solution are discussed.
Impact of partial steps and momentum advection schemes in a global ocean circulation model at eddy-permitting resolution
