TY - JOUR
T1 - Turbulent mixing on sloping bottom of an energetic tidal channel
AU - Shao, Huan Jie
AU - Tseng, Ruo Shan
AU - Lien, Ren Chieh
AU - Chang, Yu Chia
AU - Chen, Jau Ming
N1 - Funding Information:
Bottom-mounted ADCP data were kindly provided by the late Professor David Tang of the Institute of Oceanography at National Taiwan University. This work was supported by the Ministry of Science and Technology of Taiwan , Republic of China [Grant number MOST 104-2611-M-110-008 ].
Publisher Copyright:
© 2018 Elsevier Ltd
PY - 2018/8/15
Y1 - 2018/8/15
N2 - Measurements of turbulence dissipation, current, and stratification in an energetic, sloping tidal channel, the Penghu Channel (PHC), in the Taiwan Strait were conducted to investigate temporal variations of turbulence properties in the bottom boundary layer (BBL) under different stratified conditions. It was found that the PHC exhibits a unique feature of semidiurnal cycle of turbulence in the BBL due to the fact that current speeds during the flood are much higher than those during the ebb. Turbulent mixing in the BBL, produced mainly by the tidal current shear, has high values of dissipation (~10−5 W Kg−1) and eddy diffusivity and extends upward to approximately 40 m above the bottom during the flood. During the flood upslope flow, significant temperature drop and destratification of the near-bottom layer occur due to turbulence mixing associated with the shear instabilities, confirmed by the gradient Richardson number less than the critical value of 1/4. By contrast, stratification produced during the ebb is discernible only in the upper part of the BBL above the mixed layer. The stratification is weak (strong) during enhanced (suppressed) turbulence. The observed dissipation rate of turbulent kinetic energy is proportional to the cubic power of current speed, suggesting that the observed turbulence is generated via the boundary layer shear instability.
AB - Measurements of turbulence dissipation, current, and stratification in an energetic, sloping tidal channel, the Penghu Channel (PHC), in the Taiwan Strait were conducted to investigate temporal variations of turbulence properties in the bottom boundary layer (BBL) under different stratified conditions. It was found that the PHC exhibits a unique feature of semidiurnal cycle of turbulence in the BBL due to the fact that current speeds during the flood are much higher than those during the ebb. Turbulent mixing in the BBL, produced mainly by the tidal current shear, has high values of dissipation (~10−5 W Kg−1) and eddy diffusivity and extends upward to approximately 40 m above the bottom during the flood. During the flood upslope flow, significant temperature drop and destratification of the near-bottom layer occur due to turbulence mixing associated with the shear instabilities, confirmed by the gradient Richardson number less than the critical value of 1/4. By contrast, stratification produced during the ebb is discernible only in the upper part of the BBL above the mixed layer. The stratification is weak (strong) during enhanced (suppressed) turbulence. The observed dissipation rate of turbulent kinetic energy is proportional to the cubic power of current speed, suggesting that the observed turbulence is generated via the boundary layer shear instability.
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U2 - 10.1016/j.csr.2018.06.012
DO - 10.1016/j.csr.2018.06.012
M3 - Article
AN - SCOPUS:85049560099
VL - 166
SP - 44
EP - 53
JO - Continental Shelf Research
JF - Continental Shelf Research
SN - 0278-4343
ER -