Observations of Parametric Subharmonic Instability of Diurnal Internal Tides in the Northwest Pacific

Author:

Wang Yifan1,Guan Shoude12,Zhang Zhiwei12,Zhou Chun12,Xu Xin3,Guo Chuncheng45,Zhao Wei12,Tian Jiwei12

Affiliation:

1. a Frontier Science Center for Deep Ocean Multispheres and Earth System and Physical Oceanography Laboratory/Key Laboratory of Ocean Observation and Information of Hainan Province, Sanya Oceanographic Institution/Academy of the Future Ocean, Ocean University of China, Qingdao/Sanya, China

2. b Laoshan Laboratory, Qingdao, China

3. c School of Mathematical Sciences and College of Oceanic and Atmospheric Sciences, Ocean University of China, Qingdao, China

4. d Norwegian Research Centre, Bergen, Norway

5. e Bjerknes Centre for Climate Research, Bergen, Norway

Abstract

Abstract Based on yearlong observations from three moorings at 12°, 14°, and 16°N in the northwest Pacific, this study presents observational evidence for the occurrence and behavior of parametric subharmonic instability (PSI) of diurnal internal tides (ITs) both in the upper and abyssal ocean around the critical latitudes (O1 IT: 13.44°N; K1 IT: 14.52°N), which is relatively less explored in comparison with PSI of M2 ITs. At 14°N, near-inertial waves (NIWs) feature a “checkerboard” pattern with comparable upward- and downward-propagating components, while the diurnal ITs mainly feature a low-mode structure. The near-inertial kinetic energy at 14°N, correlated fairly well with the diurnal KE, is the largest among three moorings. The bicoherence analysis, and a causality analysis method newly introduced here, both show statistically significant phase locking between PSI triads at 14°N, while no significant signals emerge at 12° and 16°N. The estimated PSI energy transfer rate shows a net energy transfer from diurnal ITs to NIWs with an annual-mean value of 1.5 × 10−10 W kg−1. The highly sheared NIWs generated by PSI result in a 2–6 times larger probability of shear instability events at 14°N than 12° and 16°N. Through swinging the local effective inertial frequency close to either O1 or K1 subharmonic frequencies, the passages of anticyclonic and cyclonic eddies both result in elevated NIWs and shear instability events by enhancing PSI efficiency. Particularly, different from the general understanding that cyclonic eddies usually expel NIWs, enhanced NIWs and instability are observed within cyclonic eddies whose relative vorticity can modify PSI efficiency. Significance Statement Parametric subharmonic instability (PSI) effectively transfers energy from low-mode internal tides (ITs) to high-mode near-inertial waves (NIWs), triggering elevated mixing around critical latitudes. This study provides observational evidence for the occurrence of PSI of diurnal ITs in the northwest Pacific and its role in enhancing shear instability. Generally, anticyclonic eddies act to trap NIWs while cyclonic eddies tend to expel NIWs. Here we document elevated NIWs and shear instability within both anticyclonic and cyclonic eddies, which shift the local effective inertial frequency close to either O1 or K1 subharmonic frequencies, thereby enhancing PSI efficiency. Processes associated with PSI and the modulation of PSI efficiency by mesoscale eddies have significant implications for improving mixing parameterizations in ocean circulation and climate models.

Funder

National Natural Science Foundation of China

Publisher

American Meteorological Society

Reference73 articles.

1. Fine-structure contamination: Observations and a model of a simple two-wave case;Alford, M. H.,2001a

2. Internal swell generation: The spatial distribution of energy flux from the wind to mixed layer near-inertial motions;Alford, M. H.,2001b

3. Observations of parametric subharmonic instability of the diurnal internal tide in the South China Sea;Alford, M. H.,2008

4. Internal waves across the Pacific;Alford, M. H.,2007

5. Near-inertial internal gravity waves in the ocean;Alford, M. H.,2016

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