East‐west asymmetry in nonlinear internal waves from Luzon Strait

Abstract

[1] The nonhydrostatic Regional Ocean Modeling System is applied to study the effects of thermocline shoaling/deepening, bathymetry, and asymmetric modulated tides on the soliton growth to the west and east of Luzon Strait in the South China Sea and western Pacific Ocean. Luzon Strait comprises a shallow east ridge and a deep west ridge, and its interaction with barotropic tidal currents yields strong westward internal tides that disperse into solitons. Satellite imagery indicates that the westward solitons are more numerous and better defined than the eastward solitons. The model results show that the eastward solitons are 45%, 39%, 28%, and 23% smaller than the westward solitons due to asymmetric modulated barotropic tides at the east ridge, a deeper Pacific Ocean, westward thermocline shoaling related to the Kuroshio current, and internal tide resonance in a double ridge configuration, respectively. Due to the westward location of the Kuroshio, little thermocline deepening occurs east of the east ridge. Hence, the influence of thermocline deepening on counteracting eastward soliton growth is small. The Kuroshio mainly enhances westward soliton growth. The dispersion of internal tides into solitons is governed by the balance between the nonlinearity parameter on the one hand and the nonhydrostatic and Coriolis dispersions on the other. It is shown that this balance favors soliton growth for thermocline shoaling, while it counters it for a deeper ocean. A series of double ridge experiments is performed, in which the distance between the ridges and the height of the west ridge are varied. For a semidiurnal tidal forcing and two Gaussian ridges separated by 100 km, barotropic to baroclinic energy conversion is enhanced at both ridges, causing larger westward internal tides and solitons. The combination of Coriolis forcing, thermocline shoaling, and a double ridge configuration enhances the distinctiveness of the so-called type a and b solitons when a modulated tide occurs.

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

“…3.1 and 3.2), which is associated with the NECC. A very similar setting is also discussed in the South China Sea by Buijsman et al (2010a), where the Kuroshio Current is also associated with a density front, with important implications for ISW development there. This feature is of particular interest to this study, and its implications are further discussed in Sect.…”

The Cascade of Tidal Energy from Low to High Modes on a Continental Slope

“…These dynamics are expressed in observations of intermittent and unpredictable internaltide generation and energy fluxes (Kelly and Nash 2010;Zilberman et al 2011) and internal-tide interactions (i.e., resonance) between ridges (Buijsman et al 2010;Echeverri et al 2011). To understand and predict internal tides, there is a need to better observe and quantify the effects of preexisting internal tides on internal-tide generation and dissipation; their relevance will ultimately determine the nature and variability of the global cascade of tidal energy.…”

“…This is because internal-tide generation is a nonlinear quantity that depends on the phasing of surface-tide velocity and internal-tide bottom pressure (Kelly and Nash 2010;Buijsman et al 2010;Zilberman et al 2011). In section 3c, the sensitivity of C to the phase of the incident internal tide is examined.…”

“…Here, the cascade of tidal energy is examined for the large-scale linear tide. By neglecting nonlinearity, the physics of wave-wave interactions (Mü ller et al 1986;MacKinnon and Winters 2005;Alford et al 2007); large-amplitude internal waves (Buijsman et al 2010); and tide-topography interactions with long tidal excursions (Bell 1975), high Froude number (Legg and Klymak 2008), and turbulent boundary layers along critical slopes (Gayen and Sarkar 2010) are omitted. However, linearizing the equations of motion isolates the physics of small tidal-excursion tide-topography interactions (Garrett and Kunze 2007), which can be used to describe observed topographic scattering from rough and steep topography (Johnston et al 2003;Nash et al 2004Nash et al , 2007.…”

Characterizing the nonlinear internal wave climate in the northeastern South China Sea

“…First, there seems to be a distinct lack of eastwardpropagating waves on the Pacific side of the Luzon Ridge. This has recently been attributed to asymmetries in the tidal flux, thermal structure, and bottom topography across the ridge (Buijsman et al, 2010b) although observations on the Pacific side are lacking. Second, westward-propagating features generally do not appear in the surface imagery until a point west of the western (Heng-Chun) Ridge.…”