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Volume 25, issue 2 | Copyright

Special issue: Extreme internal wave events

Nonlin. Processes Geophys., 25, 441-455, 2018
https://doi.org/10.5194/npg-25-441-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 25 Jun 2018

Research article | 25 Jun 2018

The evolution of mode-2 internal solitary waves modulated by background shear currents

Peiwen Zhang1,3,4, Zhenhua Xu1,2,3,4, Qun Li5, Baoshu Yin1,2,3,4, Yijun Hou1,2,3,4, and Antony K. Liu6 Peiwen Zhang et al.
  • 1Key Laboratory of Ocean Circulation and Waves, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, 266071, China
  • 2Qingdao National Laboratory for Marine Science and Technology, Qingdao, 266071, China
  • 3University of the Chinese Academy of Sciences, Beijing, 100049, China
  • 4Center for Ocean Mega-Science, Chinese Academy of Sciences, Qingdao, 266071, China
  • 5Polar Research Institute of China, Shanghai, 200136, China
  • 6Ocean University of China, Qingdao, 266100, China

Abstract. The evolution of mode-2 internal solitary waves (ISWs) modulated by background shear currents was investigated numerically. The mode-2 ISW was generated by the lock-release method, and the background shear current was initialized after the mode-2 ISW became stable. Five sets of experiments were conducted to assess the sensitivity of the modulation process to the direction, polarity, magnitude, shear layer thickness and offset extent of the background shear current. Three distinctly different shear-induced waves were identified as a forward-propagating long wave, oscillating tail and amplitude-modulated wave packet in the presence of a shear current. The amplitudes of the forward-propagating long wave and the amplitude-modulated wave packet are proportional to the magnitude of the shear but inversely proportional to the thickness of the shear layer, as well as the energy loss of the mode-2 ISW during modulation. The oscillating tail and amplitude-modulated wave packet show symmetric variation when the background shear current is offset upward or downward, while the forward-propagating long wave was insensitive to it. For comparison, one control experiment was configured according to the observations of Shroyer et al. (2010); in the first 30 periods,  ∼ 36% of total energy was lost at an average rate of 9Wm−1 in the presence of the shear current; it would deplete the energy of initial mode-2 ISWs in  ∼ 4.5h, corresponding to a propagation distance of  ∼ 5km, which is consistent with in situ data.

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We perform five sets of numerical experiments to examine the evolution processes of mode-2 internal solitary waves (ISWs) modulated by background shear currents. Three distinctly different shear-induced waves were identified as forward-propagating long waves, oscillating tails and amplitude-modulated wave packets. The background shear currents are found to play an important role for the short-lived nature and energy decay process of mode-2 ISWs observed previously by Shroyer et al. (2010).
We perform five sets of numerical experiments to examine the evolution processes of mode-2...
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