Concurrent simulation of the eddying general circulation and tides in a global ocean model

Abstract

a b s t r a c tThis paper presents a five-year global simulation of HYCOM, the HYbrid Coordinate Ocean Model, that simultaneously resolves the eddying general circulation, barotropic tides, and baroclinic tides with 32 layers in the vertical direction and 1/12.5°(equatorial) horizontal grid spacing. A parameterized topographic wave drag is inserted into the model and tuned so that the surface tidal elevations are of comparable accuracy to those in optimally tuned forward tide models used in previous studies. The model captures 93% of the open-ocean sea-surface height variance of the eight largest tidal constituents, as recorded by a standard set of 102 pelagic tide gauges spread around the World Ocean. In order to minimize the impact of the wave drag on non-tidal motions, the model utilizes a running 25-h average to approximately separate tidal and non-tidal components of the near-bottom flow. In contrast to earlier high-resolution global baroclinic tide simulations, which utilized tidal forcing only, the simulation presented here has a horizontally non-uniform stratification, supported by the wind-and buoyancy forcing. The horizontally varying stratification affects the baroclinic tides in high latitudes to first order. The magnitude of the internal tide perturbations to sea surface elevation amplitude and phase in a large box surrounding Hawai'i is quite similar to that observed in satellite altimeter data, although the exact locations of peaks and troughs in the modeled perturbations differ from those in the observed perturbations.

The Unpredictable Nature of Internal Tides on Continental Shelves

“…These distantly generated motions redistribute barotropic energy globally through internal waves and mixing but remain largely indeterministic even with global internal tide models (i.e., Arbic et al 2010;Simmons et al 2004). Continental slopes and shelves represent locations where a significant fraction of baroclinic energy may be dissipated (Nash et al 2004) since internal tides are able to propagate great distances through the deep ocean waveguide (Alford et al 2007).…”

NEMO on the shelf: assessment of the Iberia–Biscay–Ireland configuration

“…The high resolution used here is expected to allow for a significant part of the tidally induced internal wave spectrum to be resolved, which in turn provides an important sink of energy for barotropic tides. In forward global tide modelling, correctly accounting for this barotropic to baroclinic conversion explicitly or through adhoc parameterizations has now become key for further improvement (Arbic et al, 2010;Lyard et al, 2006). In the next paragraphs, we examine results of a 1 yr harmonic analysis on the runbc experiment.…”

“…It is likely that, in turn, global-scale simulations will benefit from more realistic coastal modelling performance. As already explored in other models, explicit representation of tidal motions is likely to become a standard feature of global eddying models in the near future (see Arbic et al, 2010 for instance). Also, one particular aspect in the present model configuration is the relatively high (2-3 km) horizontal resolution used.…”

The effect of tides on dense water formation in Arctic shelf seas

“…At present, however, most OGCMs include a free surface and so can, in principle, accommodate tidal processes. Although model and computer advancement means that horizontal and vertical resolution are increasing in OGCMs such that the explicit inclusion of the barotropic tide is possible (Arbic et al, 2010;Thomas and Sündermann, 2001), they require substantial computer resources to run. Thus, regional models that can regularly operate on finer resolutions and shorter time steps are an efficient way to study tidal processes in Arctic shelf seas.…”