Submesoscale Turbulence over a Topographic Slope

Abstract

Abstract:Regions of the ocean near continental slopes are linked to significant vertical velocities caused by advection over a sloping bottom, frictional processes and diffusion. Oceanic motions at submesoscales are also characterized by enhanced vertical velocities, as compared to mesoscale motions, due to greater contributions from ageostrophic flows. These enhanced vertical velocities can make an important contribution to turbulent fluxes. Sloping topography may also induce large-scale potential vorticity gradients by modifying the slope of interior isopycnal surfaces. Potential vorticity gradients, in turn, may feed back on mesoscale stirring and the generation of submesoscale features. In this study, we explore the impact of sloping topography on the characteristics of submesoscale motions. We conduct high-resolution (1 km × 1 km) simulations of a wind-driven frontal current over an idealized continental shelf and slope. We explore changes in the magnitude, skewness and spectra of surface vorticity and vertical velocity across different configurations of the topographic slope and wind-forcing orientations. All of these properties are strongly modulated by the background topography. Furthermore, submesoscale characteristics exhibit spatial variability across the continental shelf and slope. We find that changes in the statistical properties of submesoscale motions are linked to mesoscale stirring responding to differences in the interior potential vorticity distributions, which are set by frictional processes at the ocean surface and over the sloping bottom. Improved parameterizations of submesoscale motions over topography may be needed to simulate the spatial variability of these features in coarser-resolution models, and are likely to be important to represent vertical nutrient fluxes in coastal waters.

Cross‐Slope Heat and Salt Transport Induced by Slope Intrusion Eddy's Horizontal Asymmetry in the Northern South China Sea

“…The modeled eddy‐induced heat and salt transport may be underestimated in our study. The horizontal resolution (10 km) of this model could resolve mesoscale eddy, but ignore the submesoscales (<10 km), such as topographic waves (Clément et al., 2016), and submesoscale eddies (Lazar et al., 2018; Su et al., 2018), etc. This may reduce the nonlinear effects on the heat/salt transport.…”

Linear stability analysis for flows over sinusoidal bottom topography

“…Irregularities in bottom topography play a pivotal role in the dynamics of the ocean's circulation (Marshall 1995;Gille, Metzger & Tokmakian 2004). It has been shown that oceanic mesoscale eddies and ubiquitous multiple alternating jets form and exhibit significant variability localised over topographic features (Thompson & Richards 2011;Boland et al 2012;Chen, Kamenkovich & Berloff 2015;Stern, Nadeau & Holland 2015;Khatri & Berloff 2018;Lazar, Zhang & Thompson 2018;Khatri & Berloff 2019). This variation in oceanic flows and flow-topographic interactions affect many processes such as the eddy-induced transport, eddy energetics and ocean ventilation (Thompson 2010;Abernathey & Cessi 2014;Barthel et al 2017;Tamsitt 2017;Youngs et al 2017;Klocker 2018).…”