Impact of Resolution on the Tropical Pacific Circulation in a Matrix of Coupled Models

• Published in: Journal of climate Vol. 22; no. 10; pp. 2541 - 2556
• Main Authors: Roberts, Malcolm J., Clayton, A., Demory, M.-E., Donners, J., Vidale, P. L., Norton, W., Shaffrey, L., Stevens, D. P., Stevens, I., Wood, R. A., Slingo, J.
• Format: Journal Article
• Language: English
• Published: Boston, MA American Meteorological Society 15.05.2009
• Subjects: Atmosphere; Atmospheric circulation; Atmospheric models; Atmospherics; Climate; Climate change; Climate models; Climatology; Climatology. Bioclimatology. Climate change; Dissipation; Earth, ocean, space; Exact sciences and technology; External geophysics; General circulation models; Geophysics. Techniques, methods, instrumentation and models; Instability waves; Instability waves (fluids); Investigations; Marine; Meteorology; Modeling; Modelling; Momentum; Ocean circulation; Ocean circulation models; Ocean currents; Ocean models; Oceans; Parametric models; Remote sensing systems; Resolution; Simulation; Simulations; Studies; Tropical circulation; Walker circulation; Weather forecasting; Equatorial Pacific; Pacific Ocean; United Kingdom > UK; Japan; IS, Tropical Pacific; Climatology; Tropical instability wave; Coupled model; General circulation models; sensitivity analysis; Climate models; digital simulation; Sea surface temperature; Ocean-atmosphere model; Walker circulation; spatial resolution; Forcing; atmospheric circulation
• ISSN: 0894-8755; 1520-0442
• DOI: 10.1175/2008jcli2537.1

Results are presented from a matrix of coupled model integrations, using atmosphere resolutions of 135 and 90 km, and ocean resolutions of 1° and 1/3°, to study the impact of resolution on simulated climate. The mean state of the tropical Pacific is found to be improved in the models with a higher ocean resolution. Such an improved mean state arises from the development of tropical instability waves, which are poorly resolved at low resolution; these waves reduce the equatorial cold tongue bias. The improved ocean state also allows for a better simulation of the atmospheric Walker circulation. Several sensitivity studies have been performed to further understand the processes involved in the different component models. Significantly decreasing the horizontal momentum dissipation in the coupled model with the lower-resolution ocean has benefits for the mean tropical Pacific climate, but decreases model stability. Increasing the momentum dissipation in the coupled model with the higher-resolution ocean degrades the simulation toward that of the lower-resolution ocean. These results suggest that enhanced ocean model resolution can have important benefits for the climatology of both the atmosphere and ocean components of the coupled model, and that some of these benefits may be achievable at lower ocean resolution, if the model formulation allows.