OCEAN MODELING IN A GLOBAL OCEAN OBSERVING SYSTEM

The oceanographic community is currently contemplating the design of a global ocean climate observing system to help monitor, describe, and understand the seasonal to decadal climate changes of the ocean and to provide the observations needed for climate prediction. This review attempts to define a role for modeling within that system, the central theme being that the observational and modeling elements must be developed in concert, with the presence of one enhancing the value of the other. Three distinct categories of model-to-data interface are identified. In the first class, models and data collection develop separately, being joined only by intermittent validation steps. In the second, and by far most important, class the model and data collection evolve together, either in a time-space data assimilation and prediction system, or through the application of inverse methods. In the final category, model information feeds back to the observing system design, and vice versa, and the model assimilation system provides quality control on the data. The key role of (atmospheric) models in the determination of surface fluxes to drive ocean models is discussed. A nontrivial role is proposed for ocean models whereby they provide additional, and largely independent, constraints on atmospheric forecast system estimates. The role of ocean models in the analysis of surface and upper ocean fields needs to be developed, particularly with respect to salinity and nonphysical fields. The use of models in rationalizing the choice of observation platforms is discussed, together with some of the difficulties in interpreting such studies. The state of tropical ocean prediction is reviewed with particular emphasis on systems that assimilate subsurface temperature data. A range of thermocline models are also reviewed with the emphasis on subduction and the problem of initializing and constraining models that resolve mesoscale eddies. Some of the issues involved in matching the models to particular observational methods, and vice versa, are discussed with respect to tropical ocean and thermocline modeling. The current state of global ocean and coupled climate general circulation models and models for studying tracer circulation and coupled physical-biological systems is evaluated. This prognostic path and the products and knowledge derived from integrations are contrasted with the inverse modeling approach which attempts to infer ocean circulation through a combination of observational and modeling constraints. Again we speculate on the model-data interface and on the different measurement strategies and data requirements. The concept of community modeling and the need for substantial resources and international organization are discussed. A case for global ocean observing system centers with colocated modeling and data collection is made, but with model diversity and individuality emphasized.