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Article

Near-inertial Wave Variability Induced by Parametric Subharmonic Instability in the Subtropical Northwestern Pacific

북서태평양 아열대 해역 PSI 기인 준관성주기 내부파의 변동성

ChaeYeon Lee1
,
Kang-Nyeong Lee1*
,
HaJin Song1
,
Eung Kim2
,
Jae-Hun Park1
이 채연1
,
이 강녕1*
,
송 하진1
,
김 응2
,
박 재훈1
1Department of Ocean Sciences, Inha University, Incheon 22212, Korea
2Marine Domain Research Division, Korea Institute of Ocean Science & Technology, Busan 49111, Korea
1인하대학교 해양과학과 (22212) 인천광역시 미추홀구 인하로 100
2한국해양과학기술원 해양영토연구본부 (49111) 부산광역시 영도구 해양로 385
*Corresponding Author
10 June 2026. pp. 1-13
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Abstract

Near-inertial waves (NIWs) are primarily driven by wind, but they can also be generated through nonlinear interactions such as Parametric Subharmonic Instability (PSI). Internal tides transfer their energy to inertial oscillations through PSI when half of the internal tide frequency matches the local inertial frequency. This study investigates PSI-induced NIW variability using ADCP mooring observations obtained at 13.6°N, 17°N, and 21°N in the northwestern Pacific from June 2010 to May 2013. Among the three sites, site M2 (13.6°N), located near the critical latitude for PSI of diurnal internal tides, exhibited persistently strong NIWs and enhanced vertical shear despite the absence of typhoon events. In addition, the NIWs at site M2 likely resulted from the PSI of diurnal internal tides because the energy peak observed in the inertial band was located at a frequency higher than the local inertial frequency. The kinetic energy of the NIWs generally followed the semi-annual variation of diurnal tides. However, from April to October 2012, inertial-band kinetic energy weakened substantially and did not follow the expected tidal variation. During the same period, opposite variations in diurnal-band kinetic energy were observed between sites M2 and M3, implying a change in the propagation path of the diurnal internal tides, likely due to weakened equatorward refraction. This study demonstrates that PSI of remotely generated diurnal internal tides is an important source of NIWs, enhanced vertical shear, and turbulent mixing, highlighting the importance of internal wave interactions in ocean circulation and underscoring the need for numerical simulations to account for these interactions.

Keywords
parametric subharmonic instability
near-inertial waves
diurnal internal tide
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Information
  • Publisher :Korea Institute of Ocean Science and Technology
  • Publisher(Ko) :한국해양과학기술원
  • Journal Title :Ocean and Polar Research
  • Journal Title(Ko) :Ocean and Polar Research
  • Volume : 48
  • Pages :1-13
  • Received Date : 2026-04-30
  • Accepted Date : 2026-05-22
  • Published Date : 2026-06-10
  • DOI :https://doi.org/10.4217/OPR.2026015
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