Impact of Parameterized Internal Wave Drag on the Semidiurnal Energy Balance in a Global Ocean Circulation Model

Abstract

The effects of a parameterized linear internal wave drag on the semidiurnal barotropic and baroclinic energetics of a realistically forced, three-dimensional global ocean model are analyzed. Although the main purpose of the parameterization is to improve the surface tides, it also influences the internal tides. The relatively coarse resolution of the model of ~8 km only permits the generation and propagation of the first three vertical modes. Hence, this wave drag parameterization represents the energy conversion to and the subsequent breaking of the unresolved high modes. The total tidal energy input and the spatial distribution of the barotropic energy loss agree with the Ocean Topography Experiment (TOPEX)/Poseidon (TPXO) tidal inversion model. The wave drag overestimates the high-mode conversion at ocean ridges as measured against regional high-resolution models. The wave drag also damps the low-mode internal tides as they propagate away from their generation sites. Hence, it can be considered a scattering parameterization, causing more than 50% of the deep-water dissipation of the internal tides. In the near field, most of the baroclinic dissipation is attributed to viscous and numerical dissipation. The far-field decay of the simulated internal tides is in agreement with satellite altimetry and falls within the broad range of Argo-inferred dissipation rates. In the simulation, about 12% of the semidiurnal internal tide energy generated in deep water reaches the continental margins.

Effect of the North Equatorial Counter Current on the generation and propagation of internal solitary waves off the Amazon shelf (SAR observations)

“…Similar results can be equally found in more recent models, which also feature the Amazon shelf break as an important hotspot for the conversion of barotropic to baroclinic energy (see e.g. Buijsman et al, 2016). The presence of ITs and ISWs has already been documented with in situ measurements (Ivanov et al, 1990;Brandt et al, 2002;Vlasenko et al, 2005) and acknowledged in remote-sensing data (see also Jackson, 2004), but no detailed description has yet emerged regarding the two-dimensional horizontal structure of the ISW field.…”

“…The characteristic soliton widths found in Fig. 6 are of the order of several kilometres, with mean distribution values amounting to 5 and 6 km for sites A and B, respectively, and hence an order of magnitude higher when compared, e.g., with the Bay of Biscay, Massachusetts Bay or the western Iberian shelf (Azevedo et al, 2006;da Silva and Helfrich, 2008;Magalhaes and da Silva, 2012). Consistently with case studies analysed in Fig.…”

“…The length scale L is considered here to be a proxy measure of the horizontal dimension of the individual solitary waves (along their propagation direction). We note that for this particular study region the majority of the case studies presented ISWs with positive backscatter variations from the unperturbed I 0 (as is defined in da Silva et al, 1998;see their Fig. 3), and hence L was generally defined as the length where normalized backscatter intensities are greater than I 0 (see dashed lines and L in Fig.…”

“…Indeed, the ISW sea surface manifestations depicted in SAR imagery are now widely documented in the literature and are essentially a result of hydrodynamic modulation of the sea surface roughness and wave breaking, provided that the wind speeds are not excessively strong (see e.g. Alpers, 1985;da Silva et al, 1998;Kudryavtsev et al, 2005).…”

“…3), as is typically done for sea surface manifestations of ISWs in SAR images (see e.g. da Silva et al, 1998). The length scale L is considered here to be a proxy measure of the horizontal dimension of the individual solitary waves (along their propagation direction).…”