Deep circulation in the South China Sea simulated in a regional model

Zhao, Xiaolong; Zhou, Chun; Xu, Xiaobiao; Ye, Ruijie; Zhao, Wei

doi:10.1007/s10236-020-01411-2

Cited by 8 publications

(6 citation statements)

References 69 publications

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“…In our model, a bottom‐intensified deep western boundary current is constrained between the 3,000‐ and 3,500‐m isobath in the northern SCS, consistent with previous model result (e.g., Zhao et al., 2020, Figure 11). However, the horizontal mean flows in the deep ocean are quite different between the two experiments.…”

Section: Discussionsupporting

confidence: 92%

The Role of Small‐Scale Topography in Modulating Eddy Scale in the Northern South China Sea

2023

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The ocean is intrinsically turbulent in nature and as a result of non-linear interactions energy in the ocean can transfer across spatial scales. Geostrophic turbulence theory predicts an inverse energy cascade (from small scales to large scales) of ocean eddy kinetic energy where the eddy length scale increases until it is halted at the Rhines scale by planetary wave propagation (Rhines, 1975;Salmon, 1998). However, satellite observations reveal that the dominate eddy scales in many regions of the oceans are only slightly larger than the local Rossby deformation radius (Stammer, 1997). This indicates that the inverse cascade is often arrested by other physical processes before it reaches the Rhines scale.For example, Arbic and Flierl (2004) found that the bottom friction, or bottom drag, can arrest the inverse cascade and thereby modulate the eddy length scale. Eddies in their model simulations tend to have larger horizontal scales than observations under weak bottom drag. Another possible candidate process that can affect eddy scale is the generation of lee waves over small-scale topography (wave drag), which is believed to be an efficient way to cascade the mesoscale energy to small-scales that are more readily to be dissipated (Nikurashin et al., 2013). The downscale or forward eddy energy cascade (from large scales to small scales) above the small-scale rough topography may contribute to the arrest of inverse cascade and thereby reduce the eddy scales. However, the manner in which wave drag affects the eddy scales may be quite different from that of bottom drag. For example, different from the bottom drag which only occurs in the bottom boundary layer, lee waves can radiate away from the ocean bottom into ocean interior and interact with the mean flows (

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Section: Discussionsupporting

confidence: 92%

The Role of Small‐Scale Topography in Modulating Eddy Scale in the Northern South China Sea

2023

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“…Assuming that diurnal internal tides westward from the Luzon Strait to the slope, their incident angles with respect to positive y direction during four diurnal springs are g 1 =23°, g 2 =40°, g 3 =51°and g 4 =43°, respectively (Figure 5C). This is consistent with the satellite altimeter observations near M1 for mode-1 internal tides (g = 46°; Zhao et al, 2020), except at the first spring during which the modal decomposition may have large errors due to the absence of the upper ADCP data.…”

Section: Overview Of Internal Tidessupporting

confidence: 90%

“…The southwestward on the deep slope may also be caused by the deep western boundary current (hereafter referred to DWBC; Wang et al, 2011;Zhou et al, 2017;Zhao et al, 2020;Zhou et al, 2020). Using mooring data collected near our mooring site M1, Zheng et al (2022) estimated that the DWBC was weak during August, 2018 corresponding to our observation period, with a velocity of 0.54 cm/s.…”

Section: Generation Of Along-slope Bottom Currentsmentioning

confidence: 95%

Along-slope bottom currents driven by dissipation of internal tides in the northeastern South China Sea

Wang

Xie²,

Li³

et al. 2023

Front. Mar. Sci.

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Recent mooring observations on the continental slope on the east side of the Dongsha Island in the northeastern South China Sea (SCS) showed that an along-slope bottom current can be generated when internal tides obliquely incident to the slope are dissipated near the seafloor. In this study, new mooring data collected on the south side of the Dongsha Island are used to explore the universality of internal wave driven the bottom currents and test the ability of the previous theory in estimating the along-slope current. The data show strong near-bottom energy dissipation due to the critical reflection of diurnal internal tides on the continental slope, with a time-mean depth-integrated dissipation rate of ~4.8×10-3 W/m2. Because of the obliquely incident of diurnal internal tides to the slope, near-bottom dissipation of internal tides generates a southwestward along-slope current, with the maximum velocity exceeding 6 cm/s. By comparing the observations, the previous theory for internal wave induced mean flows developed by Thorpe (1999) shows a good ability to estimate the along-slope bottom current velocity. Based on the theory, as well as modelled energy dissipation on the entire continental slope in the northeastern SCS, a map is obtained to quantitatively describe the along-slope bottom flow caused by internal tide breaking on the slope.

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“…The N‐S‐trending Gagua Ridge is on the west side of the mooring, approximately 300 km away from the observation site. The high Gagua Ridge significantly blocks the deep eastward current, causing a weak perennial along‐ridge current near the bottom (Kaneko et al., 2001; Xu et al., 2023; Zhao et al., 2020). Other tall or deep topographic features are far from the mooring and therefore have little influence on the observation site.…”

Section: Methodsmentioning

confidence: 99%

Influence of Lee Wave Breaking on Far‐Field Mixing in the Deep Ocean

Zheng,

Zhang,

Yang

et al. 2024

JGR Oceans

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Breaking of internal lee waves generated by flow‐topography interaction is an important driving mechanism for abyssal mixing. By assuming that lee‐wave‐driven mixing is a local process, direct measurements in the past mainly focused on the water column over rough topography. In this study, a non‐local role of lee waves on remote mixing is investigated by using mooring observations in the northwestern Philippine Basin and a series of 2‐dimensional high‐resolution numerical simulations. We find that the breaking of lee waves can generate near‐inertial waves (NIWs) which can propagate away from their generation sites. The NIWs have strong vertical shear which can significantly elevate turbulent dissipation and mixing over remote uneven seafloor. Based on the topography perturbations numerical experiments, we find that for the remote gentle topography with inverse Froude number (Fr−1) between 0 and 0.5, the arrival of upstream NIWs can elevate the near‐bottom layer (0–1,000 m above bottom) dissipation rate and vertical diffusivity by 9.2 and 10.4 times, respectively at 30–50 km away from the NIWs source. For the remote rough topography with Fr−1 between 0 and 4, the corresponding increases are 3.5 and 4.4 times, respectively. The mechanism of upstream NIWs to elevate the downstream dissipation and mixing is through strengthening the shear instability over the far‐field topography, which is associated with NIWs' interactions with the topography and the generated lee waves therein. The results of this study will provide a foundation for improving the mixing parameterizations associated with current‐topography interactions.

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Deep circulation in the South China Sea simulated in a regional model

Cited by 8 publications

References 69 publications

The Role of Small‐Scale Topography in Modulating Eddy Scale in the Northern South China Sea

The Role of Small‐Scale Topography in Modulating Eddy Scale in the Northern South China Sea

Along-slope bottom currents driven by dissipation of internal tides in the northeastern South China Sea

Influence of Lee Wave Breaking on Far‐Field Mixing in the Deep Ocean

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