Title page for etd-0429118-150531


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URN etd-0429118-150531
Author Chun-Hung Yu
Author's Email Address VisualBasic2014@gmail.com
Statistics This thesis had been viewed 5344 times. Download 116 times.
Department Department of Oceanography
Year 2017
Semester 2
Degree Master
Type of Document
Language zh-TW.Big5 Chinese
Title Mechanism of bottom convection and upwelling over continental shelf
Date of Defense 2018-05-18
Page Count 69
Keyword
  • Ekman transport
  • Eddy viscosity
  • Coastal upwelling
  • Penghu channel
  • Shear-induced convection
  • Bottom boundary layer
  • Abstract Turbulence, current, and stratification were measured in the northern section of Penghu Channel (PHC) during September 2015 and April 2016. Two datasets of current profiles and bottom temperature from bottom-mounted ADCP in summer and winter of 1999 at about 10 km north of PHC were used for bottom Ekman layer and eddy viscosity analysis. Our results indicate that the cycle of turbulence in the bottom boundary layer has a semi-diurnal period. Dissipate rate of turbulent kinetic energy, ε, is higher during the flood phase and reaches a maximum value of 2.29×〖10〗^(-5) W 〖kg〗^(-1). Turbulent layer extends from the bottom to a height of 40 m, is produced primarily by vertical shear of tidal currents. Density profiles show that stratification is eroded within depths of 80-105 m during the flood, and the bottom layer becomes well mixed during the ebb. Temperature observations from the bottom-mounted ADCP reveal periodic occurrence of temperature decrease of 2-3℃ during the flood, implying shear-induced convective cooling near the bottom during the upslope flow. This phenomenon is more prominent in the summer which contributes to the along-channel upwelling in the PHC. Ekman veering of the current profiles near the bottom occurs periodically with tidal oscillation and is more obvious when the flow speed is less than 1 m s-1 during the summer. A comparison of the profiles of estimated eddy viscosity and observed eddy diffusivity indicates that the orders of magnitude of these two quantities are close. Eddy viscosity has a maximum value at the bottom and decreases upward. In summary, the combining effect of along-channel, shear-induced convection and the cross-channel, bottom Ekman dynamics will act sequentially and periodically to promote upwelling in the PHC.
    Advisory Committee
  • Guan-Yu Chen - chair
  • Jian-Ming Liau - co-chair
  • Yiing-Jang Yang - co-chair
  • Ruo-Shan Tseng - advisor
  • Files
  • etd-0429118-150531.pdf
  • indicate access worldwide
    Date of Submission 2018-05-29

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