Abstract
Abstract. Four global ocean/sea-ice simulations driven by the same realistic 47-year daily atmospheric forcing were performed by the DRAKKAR group at 2°, 1°, &frac12°, and ¼° resolutions. Simulated mean sea-surface heights (MSSH) and sea-level anomalies (SLA) are collocated over the period 1993–2004 onto the AVISO dataset. MSSH fields are compared with an inverse estimate. SLA datasets are filtered and compared over various time and space scales with AVISO regarding three characteristics: SLA standard deviations, spatial correlations between SLA variability maps, and temporal correlations between observed and simulated band-passed filtered local SLA timeseries. Beyond the 2°−1° transition whose benefits are moderate, further increases in resolution and associated changes in subgrid scale parameterizations simultaneously induce (i) strong increases in SLA standard deviations, (ii) strong improvements in the spatial distribution of SLA variability, and (iii) slight decreases in temporal correlations between observed and simulation SLA timeseries. These 3 effects are not only clear on mesoscale (14–180 days) and quasi-annual (5–18 months) fluctuations, but also on the slower (interannual), large-scale variability ultimately involved in ocean-atmosphere coupled processes. Most SLA characteristics are monotonically affected by successive resolution increases, but irregularly and with a strong dependance on frequency and latitude. Benefits of enhanced resolution are greatest in the 1°−½° and ½°−¼° transitions, in the 14–180 day range, and within eddy-active mid- and high-latitude regions. In the real ocean, most eddy-active areas are characterized by a strong SLA variability at all timescales considered here; this localized, broad-banded temporal variability is only captured at ¼° resolution.
Highlights
The choice of ocean/sea-ice primitive equation model configurations for global climate-oriented studies generally results from a compromise between the range of time and space scales to be simulated and the available computer resources.Laminar ocean models (1◦-resolution and coarser) do not explicitly resolve mesoscale eddies and fluxes: subgridscale diffusive and advective (e.g.Gent and McWilliams, 1990, noted GM90 hereafter) parameterizations are used to mimick certain down-gradient eddy fluxes
We focus on interannual timescales at which the impact of ocean model resolution has not been quantitatively assessed
These zonally-extended maxima are present in the four simulations; their magnitude reach about 70 to 85% of observed levels, except in the 2◦ model where it drops by another 10%
Summary
The choice of ocean/sea-ice primitive equation model configurations for global climate-oriented (multidecadal or longer) studies generally results from a compromise between the range of time and space scales to be simulated and the available computer resources. Resolving wide western boundary currents in coarse-resolution models requires strong viscosity values, which damp a substantial part of the currents’ variability Because they are computationally-effective, laminar oceans are being used in most global coupled models to address paleoclimatic and prediction issues (i.e. IPCC). Global eddy-admitting models presently appear as an interesting trade-off between available computer resources, the partial resolution of mesoscale effects, and the need to perform several multi-decadal integrations to study climate-related oceanic changes.
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