Sea Surface Signature of Internal Tides

Abstract

The upper ocean is energetic at scales below the Rossby deformation radius owing to the existence of internal waves and submesoscale fronts and vortices. These contribute significantly to energy dissipation, tracer mixing, and exchanges between the ocean surface layer, the ocean interior, and the atmospheric boundary layer. Internal waves and submesoscale motions both undergo strong spatial and seasonal variations, driven by different mechanisms. Here, we investigate the sea surface signature of internal waves and its seasonality using linear wave theory and a high‐resolution realistic simulation. In summer, internal waves are greatly amplified near the surface mostly due to a thin mixed layer bounded by a seasonal pycnocline. This surface amplification is well captured by linear theory, provided that the stratification at the base of the mixed layer is accurately represented. In winter, the superinertial motions are not fully explained by linear theory, reflecting impacts of the more energetic submesoscale motions.

Scale-dependent analysis of in situ observations in the mesoscale to submesoscale range around New Caledonia

“…However, the seasonality of IGWs and SM motions has been shown to be out of phase near the surface, with SM motions being the most energetic in late winter/early spring while IGWs are amplified during summer (Callies et al, 2015;Rocha et al, 2016;Qiu et al, 2018;Lahaye et al, 2019). Our estimate of the surface APE is maximum during the cool season, consistent with SM motions energised in late winter by mixed layer instabilities.…”

“…Our estimate of the surface APE is maximum during the cool season, consistent with SM motions energised in late winter by mixed layer instabilities. Lahaye et al (2019) demonstrate that the amplification/dampening of IGWs at the surface compared to the interior is captured by a linear IGW model. Based on this model, they estimate global maps of the horizontal KE ratio between the surface and the interior: the ratio of mode 1 shows weak seasonality around New Caledonia, but higher modes (2, 3 and 4) have a higher ratio (i.e., amplification) during February.…”

Scale-dependent analysis of in situ observations in the mesoscale to submesoscale range around New Caledonia

“…However, the seasonality of IGWs and SM motions has been shown to be out of phase near the surface, with SM motions being the most energetic in late winter/early spring, while IGWs are amplified during summer (Callies et al, 2015;Rocha et al, 2016;Qiu et al, 2018;Lahaye et al, 2019). Our estimate of the surface APE is maximum during the cool season, consistent with SM motions energised in late winter by mixed layer instabilities.…”

“…Our estimate of the surface APE is maximum during the cool season, consistent with SM motions energised in late winter by mixed layer instabilities. Lahaye et al (2019) demonstrate that the amplification/dampening of IGWs at the surface compared to the interior is captured by a linear IGW model. Based on this model, they estimate global maps of the horizontal KE ratio between the surface and the interior: the ratio of mode 1 shows weak seasonality around New Caledonia, but higher modes (2, 3 and 4) have a higher ratio (i.e.…”

“…LatMix, Shcherbina et al, 2014). Although those SM turbulent features represent less kinetic energy (KE) that ME eddies, they may have substantial impacts on heat transport and air-sea heat fluxes (Su et al, 2018), on upper ocean restratification (Boccaletti et al, 2007) and on biogeochemistry processes such as primary production (Mahadevan, 2016;Lévy et al, 2012).…”