The Turbulent Structure of the Marine Atmospheric Boundary Layer During and Before a Cold Front

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  • 1 School of Marine Science, Sun Yat-Sen University, Zhuhai, China.
  • 2 Ocean College, Zhejiang University, Zhoushan, China.
  • 3 Ocean Research Center of Zhou Shan, Zhejiang University, Zhoushan, China.
  • 4 Guangzhou Institute of Tropical and Marine Meteorology, CMA, Guangdong, China.
  • 5 Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China.
  • 6 Cooperative Institute for Marine and Atmospheric Studies, University of Miami, and Hurricane Research Division, AOML, NOAA, Florida, USA.
  • 7 Key Laboratory of Ocean Circulation and Waves, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, China.
  • 8 Laboratory for Ocean and Climate Dynamics, Qingdao National Laboratory for Marine Science and Technology, Qingdao, China.
  • 9 Center for Ocean Mega-Science, Chinese Academy of Sciences, Qingdao, China.
  • 10 Hong Kong Observatory, 134A Nathan Road, Kowloon, Hong Kong, China.
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Abstract

The turbulent structure within the marine atmospheric boundary layer is investigated based on four levels of observations at a fixed marine platform. During and before a cold front, the ocean surface is dominated by wind sea and swell waves, respectively, affording the opportunity to test the theory recently proposed in laboratory experiments or for flat land surfaces. The results reveal that the velocity spectra follow a k-1 law within the intermediate wavenumber (k) range immediately below inertial subrange during the cold front. A logarithmic height dependence of the horizontal velocity variances is also observed above the height of 20 m, while the vertical velocity variances increase with increasing height following a power law of 2/3. These features confirm the Attached Eddy Model and the “top-down model” of turbulence over the ocean surface. However, the behavior of velocity variances under swell conditions is much different from those during the cold front, although a remarkable k-1 law can be observed in the velocity spectra. The quadrant analysis of the momentum flux also shows a significantly different result for the two conditions.

Corresponding author: Zhongshui Zou (zouzhongshui@126.com)

Abstract

The turbulent structure within the marine atmospheric boundary layer is investigated based on four levels of observations at a fixed marine platform. During and before a cold front, the ocean surface is dominated by wind sea and swell waves, respectively, affording the opportunity to test the theory recently proposed in laboratory experiments or for flat land surfaces. The results reveal that the velocity spectra follow a k-1 law within the intermediate wavenumber (k) range immediately below inertial subrange during the cold front. A logarithmic height dependence of the horizontal velocity variances is also observed above the height of 20 m, while the vertical velocity variances increase with increasing height following a power law of 2/3. These features confirm the Attached Eddy Model and the “top-down model” of turbulence over the ocean surface. However, the behavior of velocity variances under swell conditions is much different from those during the cold front, although a remarkable k-1 law can be observed in the velocity spectra. The quadrant analysis of the momentum flux also shows a significantly different result for the two conditions.

Corresponding author: Zhongshui Zou (zouzhongshui@126.com)
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