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On the variation of dissipation flux coefficient in the upper South China Sea

Jianing LiaCollege of Oceanic and Atmospheric Sciences/Physical Oceanography Laboratory/Institute for Advanced Ocean Study/Sanya Oceanographic Institution, Ocean University of China, Qingdao/Sanya, China

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Qingxuan YangaCollege of Oceanic and Atmospheric Sciences/Physical Oceanography Laboratory/Institute for Advanced Ocean Study/Sanya Oceanographic Institution, Ocean University of China, Qingdao/Sanya, China
bLaboratory for Ocean Dynamics and Climate, Pilot National Laboratory for Marine Science and Technology, Qingdao, China

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Hui SunaCollege of Oceanic and Atmospheric Sciences/Physical Oceanography Laboratory/Institute for Advanced Ocean Study/Sanya Oceanographic Institution, Ocean University of China, Qingdao/Sanya, China

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Shuwen ZhangcInstitute of Marine Science, Shantou University, Shantou, China

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Lingling XiedLaboratory for Coastal Ocean Variation and Disaster Prediction, College of Ocean and Meteorology, Guangdong Ocean University, Zhanjiang, China
eGuangdong Key Laboratory of Climate, Resources and Environment in Continental Shelf Sea and Deep Ocean, Zhanjiang, China

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Qingye WangbLaboratory for Ocean Dynamics and Climate, Pilot National Laboratory for Marine Science and Technology, Qingdao, China
fKey Laboratory of Ocean Circulation and Waves, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, China
gUniversity of Chinese Academy of Sciences, Beijing, China

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Wei ZhaoaCollege of Oceanic and Atmospheric Sciences/Physical Oceanography Laboratory/Institute for Advanced Ocean Study/Sanya Oceanographic Institution, Ocean University of China, Qingdao/Sanya, China
bLaboratory for Ocean Dynamics and Climate, Pilot National Laboratory for Marine Science and Technology, Qingdao, China

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Jiwei TianaCollege of Oceanic and Atmospheric Sciences/Physical Oceanography Laboratory/Institute for Advanced Ocean Study/Sanya Oceanographic Institution, Ocean University of China, Qingdao/Sanya, China
bLaboratory for Ocean Dynamics and Climate, Pilot National Laboratory for Marine Science and Technology, Qingdao, China

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Abstract

This study focuses on the statistical features of dissipation flux coefficient Г in the upper South China Sea (SCS). Based on the microscale measurements collected at 158 stations in the upper SCS and derived dissipation rates of TKE and temperature variance ε and χT, via a modified method, we estimate Г and analyze its spatiotemporal variation in an energetic region and a quiescent region. We show that Г is highly variable, which scatters over three orders of magnitude from 10−2 to 101 in both regions. Г in the energetic region is slightly greater than that in the quiescent region; their median values are 0.23 and 0.17, respectively. Vertically, Г presents a clear increasing tendency with depth in both regions, though increasing rate is greater in the energetic region than in the quiescent region. In the upper SCS, Г positively depends on the buoyancy Reynolds number Reb and negatively depends on the ratio of the Ozmidov scale to the Thorpe scale, ROT, and is scaled as Г α Reb1/2. ROT−4/3, which holds for both regions. The vertical decreasing of ROT is observed, which yields parameterization of ROT =10−0.002z; this parameterization improves the performance of the Thorpe-scale method by reducing at least 50% of the bias between the observed and parameterized ε. These results shed new light on the spatiotemporal variability and modulating mechanism of Г in the upper ocean.

Corresponding author: Q. Yang, yangqx@ouc.edu.cn; H. Sun, sunhui@ouc.edu.cn

Abstract

This study focuses on the statistical features of dissipation flux coefficient Г in the upper South China Sea (SCS). Based on the microscale measurements collected at 158 stations in the upper SCS and derived dissipation rates of TKE and temperature variance ε and χT, via a modified method, we estimate Г and analyze its spatiotemporal variation in an energetic region and a quiescent region. We show that Г is highly variable, which scatters over three orders of magnitude from 10−2 to 101 in both regions. Г in the energetic region is slightly greater than that in the quiescent region; their median values are 0.23 and 0.17, respectively. Vertically, Г presents a clear increasing tendency with depth in both regions, though increasing rate is greater in the energetic region than in the quiescent region. In the upper SCS, Г positively depends on the buoyancy Reynolds number Reb and negatively depends on the ratio of the Ozmidov scale to the Thorpe scale, ROT, and is scaled as Г α Reb1/2. ROT−4/3, which holds for both regions. The vertical decreasing of ROT is observed, which yields parameterization of ROT =10−0.002z; this parameterization improves the performance of the Thorpe-scale method by reducing at least 50% of the bias between the observed and parameterized ε. These results shed new light on the spatiotemporal variability and modulating mechanism of Г in the upper ocean.

Corresponding author: Q. Yang, yangqx@ouc.edu.cn; H. Sun, sunhui@ouc.edu.cn
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