Influence of Abyssal Mixing on the Multilayer Circulation in the South China Sea

AbstractBy parameterizing the abyssal mixing as the exchange velocity (entrainment/detrainment) between the middle and deep layers of the South China Sea (SCS), its effects on the multilayer circulation are examined. Results indicate that the cyclonic circulation in the deep SCS appears only when the mixing induces an entrainment of at least 0.72 Sv (1 Sv ≡ 106 m3 s−1) from the deep to the middle layer, which is equivalent to a diapycnal diffusivity of 0.65 × 10−3 m2 s−1 or a net input rate of gravitational potential energy (GPE) of 6.89 GW, respectively. It is also found that tidal mixing in the SCS is stronger than the threshold for the generation of the cyclonic abyssal circulation, but the pattern and evolution of the deep circulation and meridional overturning circulation also depend on the spatiotemporal variability of the mixing. Moreover, the abyssal mixing is able to intensify the anticyclonic circulation in the middle layer but weaken the cyclonic circulation in the upper layer. Vorticity analysis suggests that the upward net flux induced by the abyssal mixing leads to vortex stretching (squeezing) and modulates the pressure gradient by redistributing the layer thickness, hence affects the pattern and strength of the circulation in the middle (deep) layer of the SCS, respectively. The depth-integrated effect of the thickness variation can modulate the pressure gradient across all layers and hence influence the upper-layer circulation.

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Impact of Tidal Mixing on Water Mass Transformation and Circulation in the South China Sea

Journal of Physical Oceanography ◽

10.1175/jpo-d-16-0171.1 ◽

2017 ◽

Vol 47 (2) ◽

pp. 419-432 ◽

Cited By ~ 16

Author(s):

Xiaowei Wang ◽

Zhiyu Liu ◽

Shiqiu Peng

Keyword(s):

South China Sea ◽

Density Gradient ◽

South China ◽

Water Mass ◽

The South China Sea ◽

Tidal Mixing ◽

The South ◽

China Sea ◽

Mass Properties ◽

Water Mass Transformation

AbstractUsing a high-resolution regional ocean model, the impact of tidal mixing on water mass transformation and circulation in the South China Sea (SCS) is investigated through a set of numerical experiments with different configurations of tide-induced diapycnal diffusivity. The results show that including tidal mixing in both the Luzon Strait (LS) and SCS has significant impact on the LS transport and the intermediate–deep layer circulation in the SCS Basin. Analysis of the density field indicates that tidal mixing in both the LS and SCS are essential for sustaining a consistent density gradient and thus a persistent outward-directed baroclinic pressure gradient both between the western Pacific and LS and between the LS and SCS Basin, so as to maintain the strong deep-water transport through the LS. Further analysis of water mass properties suggests that tidal mixing in the deep SCS would strengthen the horizontal density gradient, intensify the basin-scale cyclonic circulation, induce more vigorous overturning, as well as generate the subbasin-scale eddies in the abyssal SCS. The results imply that tidal mixing in both the LS and SCS plays a key dynamic role in controlling water mass properties and deep circulation features in the SCS and thus need to be deliberately parameterized in ocean circulation models for this region.

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Tidal Mixing in the South China Sea: An Estimate Based on the Internal Tide Energetics

Journal of Physical Oceanography ◽

10.1175/jpo-d-15-0082.1 ◽

2016 ◽

Vol 46 (1) ◽

pp. 107-124 ◽

Cited By ~ 28

Author(s):

Xiaowei Wang ◽

Shiqiu Peng ◽

Zhiyu Liu ◽

Rui Xin Huang ◽

Yu-Kun Qian ◽

...

Keyword(s):

South China Sea ◽

South China ◽

Dissipation Rate ◽

Internal Tide ◽

The South China Sea ◽

Internal Tides ◽

Tidal Mixing ◽

The South ◽

China Sea ◽

Diapycnal Diffusivity

AbstractBy taking into account the contributions of both locally and remotely generated internal tides, the tidal mixing in the Luzon Strait (LS) and the South China Sea (SCS) is investigated through internal-tide simulation and energetics analysis. A three-dimensional nonhydrostatic high-resolution model driven by four primary tidal constituents (M2, S2, K1, and O1) is used for the internal-tide simulation. The baroclinic energy budget analysis reveals that the internal tides radiated from the LS are the dominant energy source for the tidal dissipation in the SCS. In the LS, the estimated depth-integrated turbulent kinetic energy dissipation exceeds O(1) W m−2 atop the two subsurface ridges, with a dissipation rate of >O(10−7) W kg−1 and diapycnal diffusivity of ~O(10−2) m2 s−1. In the SCS, the most intense turbulence occurs in the deep-water basin with a dissipation rate of O(10−8–10−6) W kg−1 and diapycnal diffusivity of O(10−3–10−1) m2 s−1 within the ~2000-m water column above the seafloor as well as in the shelfbreak region with a dissipation rate of O(10−7–10−6) W kg−1 and diapycnal diffusivity of O(10−4–10−3) m2 s−1. These estimated values are consistent with observations reported in previous studies and are at least one order of magnitude larger than those based solely on locally generated internal tides.

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A Climatological Monsoon Break in Rainfall over Indochina—A Singularity in the Seasonal March of the Asian Summer Monsoon

Journal of Climate ◽

10.1175/jcli3724.1 ◽

2006 ◽

Vol 19 (8) ◽

pp. 1545-1556 ◽

Cited By ~ 50

Author(s):

Hiroshi G. Takahashi ◽

Tetsuzo Yasunari

Keyword(s):

South China Sea ◽

Summer Monsoon ◽

South China ◽

Cyclonic Circulation ◽

The South China Sea ◽

Monsoon Circulation ◽

Mountain Range ◽

The South ◽

China Sea ◽

Seasonal March

Abstract This study investigated the climatological pentad mean annual cycle of rainfall in Thailand and the associated atmospheric circulation fields. The data used included two different data of rainfall: rain gauge data for Thailand from the Thai Meteorological Department and satellite-derived rainfall data from the Climate Prediction Center (CPC) Merged Analysis of Precipitation (CMAP). Climatological mean pentad values of rainfall taken over 50 yr clearly show a distinct climatological monsoon break (CMB) occurring over Thailand in late June. The occurrence of the CMB coincides with a drastic change of large-scale monsoon circulation in the seasonal march. The CMB is a significant singularity in the seasonal march of the Southeast Asia monsoon, which divides the rainy season into the early monsoon and the later monsoon over the Indochina Peninsula. A quasi-stationary ridge dynamically induced by the north–south-oriented mountain range in Indochina is likely to cause the CMB. The formation of the strong ridge over the mountain ranges of Indochina is preceded by a sudden enhancement (northward expansion) of the upstream monsoon westerlies along a latitudinal band between 15° and 20°N in late June. The CMB also has an impact downstream. The orographically induced stationary Rossby waves enhance the cyclonic circulation to the lee of Indochina, and over the South China Sea. The enhancement of cyclonic circulation may be responsible for the summer monsoon rains peaking in late June over the South China Sea and the western North Pacific, and in the baiu front.

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