Articles | Volume 8, issue 2
Development and technical paper
19 Feb 2015
Development and technical paper |  | 19 Feb 2015

MetUM-GOML1: a near-globally coupled atmosphere–ocean-mixed-layer model

L. C. Hirons, N. P. Klingaman, and S. J. Woolnough

Abstract. Well-resolved air–sea interactions are simulated in a new ocean mixed-layer, coupled configuration of the Met Office Unified Model (MetUM-GOML), comprising the MetUM coupled to the Multi-Column K Profile Parameterization ocean (MC-KPP). This is the first globally coupled system which provides a vertically resolved, high near-surface resolution ocean at comparable computational cost to running in atmosphere-only mode. As well as being computationally inexpensive, this modelling framework is adaptable – the independent MC-KPP columns can be applied selectively in space and time – and controllable – by using temperature and salinity corrections the model can be constrained to any ocean state.

The framework provides a powerful research tool for process-based studies of the impact of air–sea interactions in the global climate system. MetUM simulations have been performed which separate the impact of introducing interannual variability in sea surface temperatures (SSTs) from the impact of having atmosphere–ocean feedbacks. The representation of key aspects of tropical and extratropical variability are used to assess the performance of these simulations. Coupling the MetUM to MC-KPP is shown, for example, to reduce tropical precipitation biases, improve the propagation of, and spectral power associated with, the Madden–Julian Oscillation and produce closer-to-observed patterns of springtime blocking activity over the Euro-Atlantic region.

Short summary
Atmosphere-ocean interactions are best isolated in models rather than observations, but state-of-the-art models are expensive and often simulate these interactions poorly. We present a less expensive modelling framework that resolves air-sea interactions well, and permits a more rigorous identification of these interactions' effects than previously possible. In our model, air-sea interactions improve tropical rainfall variations but have limited effects on midlatitude jet streams.