Energetics of Barotropic and Baroclinic Tides in the Monterey Bay Area

Abstract

A detailed energy analysis of the barotropic and baroclinic M2 tides in the Monterey Bay area is performed. The authors first derive a theoretical framework for analyzing internal tide energetics based on the complete form of the barotropic and baroclinic energy equations, which include the full nonlinear and nonhydrostatic energy flux contributions as well as an improved evaluation of the available potential energy. This approach is implemented in the Stanford Unstructured Nonhydrostatic Terrain-Following Adaptive Navier–Stokes Simulator (SUNTANS). Results from three-dimensional, high-resolution SUNTANS simulations are analyzed to estimate the tidal energy partitioning among generation, radiation, and dissipation. A 200 km × 230 km domain including all typical topographic features in this region is used to represent the Monterey Bay area. Of the 152-MW energy lost from the barotropic tide, approximately 133 MW (88%) is converted into baroclinic energy through internal tide generation, and 42% (56 MW) of this baroclinic energy radiates away into the open ocean. The tidal energy partitioning depends greatly on the topographic features. The Davidson Seamount is most efficient at baroclinic energy generation and radiation, whereas the Monterey Submarine Canyon acts as an energy sink. Energy flux contributions from nonlinear and nonhydrostatic effects are also examined. In the Monterey Bay area, the nonlinear and nonhydrostatic contributions are quite small. Moreover, the authors investigate the character of internal tide generation and find that in the Monterey Bay area the generated baroclinic tides are mainly linear and in the form of internal tidal beams. Comparison of the modeled tidal conversion to previous theoretical estimates shows that they are consistent with one another.

Tidal forcing, energetics, and mixing near the Yermak Plateau

“…Negative conversion rates seen in Fig. 6 are typical of numerical studies on internal tide energetics (Simmons et al, 2004;Kang and Fringer, 2012). A negative conversion occurs when energy is transferred from baroclinic tide to the barotropic tide and indicates interaction between locally and remotely generated baro- can be observed on the western part of the plateau around 82 • N, and also along the shelf break north of Spitsbergen.…”

“…The simulated tidal energy flux and conversion of barotropicto-baroclinic tidal energy are computed from the model by using the derivations presented in Kang and Fringer (2012). The vertically integrated, barotropic-to-baroclinic tidal energy conversion rates are obtained from…”

“…We further derive baroclinic radiation defined as the horizontal divergence of the baroclinic energy flux, ∇ H ·F , and define the depth-integrated dissipation, C −∇ H ·F , as the difference between tidal energy conversion and radiation (e.g. Kang and Fringer, 2012 …”

Transition from partly standing to progressive internal tides in Monterey Submarine Canyon

“…It is the largest submarine canyon along the west coast of the United States and has been the focus of several internal tide observational programs (Key, 1999;Kunze et al, 2002;Johnston et al, 2011;Kunze et al, 2012) and numerical modelling studies (Petruncio et al, 2002;Jachec et al, 2006;Wang et al, 2009;Kang and Fringer, 2012). In stratified seas, barotropic (surface) tidal flow across the sloping topography typical of submarine canyons can generate internal tides (internal gravity waves with tidal frequencies) by vertically displacing density surfaces (Bell, 1975;Baines, 1982).…”

“…Numerical modelling studies of internal tides in the MSC region (Jachec et al, 2006;Carter, 2010;Hall and Carter, 2011;Kang and Fringer, 2012) have shown that the internal tide observed in the canyon is likely generated on Sur Slope, roughly 40 km to the south of the canyon mouth. Hall and Carter (2011) presented evidence that more remote generation sites in the region, including two offshore seamounts, have only a minor influence on the internal tide in the canyon.…”