Distribution of near-inertial waves in the mixed and deep layers of the East/Japan Sea using a high-resolution wind-forced ocean model

Previous observations of deep near-inertial waves in the East/Japan Sea showed that they were more energetic in the southern region than in the northern region. The significant variation of surface currents in the southern region was suggested to be the cause of this meridionally asymmetric distribution of near-inertial waves, but no clear dynamic explanations were provided. In this study, we investigate the characteristics of near-inertial wave energy distribution in the East/Japan Sea using high-resolution wind-forced ocean model outputs.ted to be the cause of this meridionally asymmetric distribution of near-inertial waves, but no clear dynamic explanations were provided. In this study, we investigate the characteristics of near-inertial wave energy distribution in the East/Japan Sea using high-resolution wind-forced ocean model outputs.1

Observation and simulation of internal tides on the continental slope of the southwestern East Sea

Internal tides near the continental slope of the southwestern East Sea are investigated using two sets of 25-hour-long hourly CTD and LADCP profiles obtained during spring and neap tidal periods. The profiles span the whole water column from the surface to about 260 m. Semi-diurnal internal tide is the strongest below the main thermocline (150&#8722 200 m) where the observed 5oC isotherm displacement is more than 50 m. The Richardson numbers show low values (0&#8722 0.25) in layers where large vertical displacements occur, suggesting that internal tides could be a major process for ocean mixing around the observation site. Numerical simulations using an idealized vertical 2.5-dimensional numerical model based on the ROMS reveal that semi-diurnal internal tides are dominantly generated close to the observation site. Simulations using different configurations are also conducted for further understanding of internal tide generation mechanism and its impact on ocean mixing in this region.1

Seasonal patterns of diel vertical migration of zooplankton derived from acoustic backscatters in Okinawa Trough: Preliminary results

This study investigates the seasonal patterns of diel vertical migration (DVM) of zooplankton using one year-long (from June 2015 to June 2016) moorings deployed in Okinawa Trough. At mooring stations of KCM1 (25.88°N, 125.21°E, depth: ∼2,000 m), close to the Kuroshio core, and KCM2 (25.60°N, 125.32°E, depth: ∼2,000 m), the profiles of water velocities and acoustic backscatter strength were measured by an upward-looking, 75-kHz acoustic Doppler current profiler. Time series of acoustic backscatter strength exhibited a distinct pattern of DVM, which should be generated by zooplankton migration between pelagic (about 100 m) and mesopelagic (about 400 m) zones. A deep scattering layer (DSL) existed between 400 and 500 m during the entire moored period. Compared to summer, the DSL depth decreased about 50 m, and the zooplankton’s residual time decreased about an hour around 400 m at both stations during winter. There were different seasonal patterns in water velocities and DVM speed between KCM1 and KCM2. At KCM1, from summer to winter, depth-averaged water velocities decreased from 0.76 to 0.67 m/s, and the ascending speeds of zooplankton decreased from 30 to 10 mm/s. At KCM2,on the other hand, both of them showed almost identical values between summer and winter. The different responses between KCM1 and KCM2 are coherently related with the influence of Kuroshio current and solar radiation intensity. The details2

Effects of mesoscale circulation on nonlinear internal waves in the South China Sea from observations and simulations

This study presents observations of nonlinear internal waves acquired from a 2-D array of pressure-recording inverted echo sounders (PIESs) in the deep basin of the northeastern South China Sea for about 4 months in 2011, with the goal of assessing their propagation features affected by mesoscale circulations. The 2-D array measurements reveal that the northern side of the northeastern South China Sea is dominated by semidiurnal fluctuations, while its southern side is dominated by diurnal ones. The outputs from SUNTANS, a nonhydrostatic and unstructured grid ocean model, agree well with the observed nonlinear internal waves overall with some amplitude and arrival time deviations. We obtain time series of the deviations between our observations and the SUNTANS model simulations at each PIES site. Since the model was run with a horizontally homogeneous temperature profile obtained from a mean of historical observations, the deviations are analyzed in terms of mesoscale variability based on the data-assimilated HYCOM simulation results. We find that the amplitude and arrival time of nonlinear internal waves observed at PIES sites modulate significantly depending on time, which is associated with mesoscale circulation changes during the observation period. Deviations of internal wave arrival time are quite well simulated when they are derived from integration of the first internal-mode phase speed along 2-D ray-traced pssessing their propagation features affected by mesoscale circulations. The 2-D array measurements reveal that the northern side of the northeastern South China Sea is dominated by semidiurnal fluctuations, while its southern side is dominated by diurnal ones. The outputs from SUNTANS, a nonhydrostatic and unstructured grid ocean model, agree well with the observed nonlinear internal waves overall with some amplitude and arrival time deviations. We obtain time series of the deviations between our observations and the SUNTANS model simulations at each PIES site. Since the model was run with a horizontally homogeneous temperature profile obtained from a mean of historical observations, the deviations are analyzed in terms of mesoscale variability based on the data-assimilated HYCOM simulation results. We find that the amplitude and arrival time of nonlinear internal waves observed at PIES sites modulate significantly depending on time, which is associated with mesoscale circulation changes during the observation period. Deviations of internal wave arrival time are quite well simulated when they are derived from integration of the first internal-mode phase speed along 2-D ray-traced p1

Internal tides and ocean mixing on the ontinental shelf of the southwestern East/Japan Sea from observation and simulation

We investigate internal tides and ocean mixing near the continental slope of the southwestern East/Japan Sea using two sets of 25-hr long hourly CTD and LADCP profiles and numerical imulations. The time series of profiles span the whole water column from the surface to about 260 m during spring and neap tidal periods. Our observations reveal strong semi-diurnal internal tides below the main thermocline (150-200 m) where the 5¨&not C-isotherm displaces more than 50 m. The Richardson numbers calculated from the observations show low values (0-0.25) in layers where large vertical displacements exist, suggesting internal tide induced mixing. Numerical simulations using an idealized vertical 2.5-dimensional numerical model based on the ROMS reveal that semi-diurnal internal tide is dominantly generated on the continental slope. Simulations using different configurations are conducted for further understanding of internal tide generation mechanism and its impact on ocean mixing in this region.er column from the surface to about 260 m during spring and neap tidal periods. Our observations reveal strong semi-diurnal internal tides below the main thermocline (150-200 m) where the 5¨&not C-isotherm displaces more than 50 m. The Richardson numbers calculated from the observations show low values (0-0.25) in layers where large vertical displacements exist, suggesting internal tide induced mixing. Numerical simulations using an idealized vertical 2.5-dimensional numerical model based on the ROMS reveal that semi-diurnal internal tide is dominantly generated on the continental slope. Simulations using different configurations are conducted for further understanding of internal tide generation mechanism and its impact on ocean mixing in this region.1

Properties of internal tides observed in the southwestern part of the East Sea

We investigated the properties of internal tides observed near the continental slope of the southwestern East/Japan Sea using two sets of 25-hr long hourly CTD and LADCP profiles and numerical simulations. The profiles spanned the whole water column from the surface to about 260m depth. A semi-diurnal internal tide was strongest below the main thermocline (150-200m) where the 5ºC isotherm was displaced more than 50m. The Richardson numbers were low (0-0.25) in layers where large vertical displacements were observed, suggesting internal tide induced mixing. Numerical simulations using an idealized vertical 2.5-dimensional numerical model based on the ROMS revealed that the semi-diurnal internal tide was predominantly generated on the continental slope. By analyzing the observed data and model results, we were able to investigate the internal tide generation mechanism and its impact on ocean mixing in this regioner column from the surface to about 260m depth. A semi-diurnal internal tide was strongest below the main thermocline (150-200m) where the 5ºC isotherm was displaced more than 50m. The Richardson numbers were low (0-0.25) in layers where large vertical displacements were observed, suggesting internal tide induced mixing. Numerical simulations using an idealized vertical 2.5-dimensional numerical model based on the ROMS revealed that the semi-diurnal internal tide was predominantly generated on the continental slope. By analyzing the observed data and model results, we were able to investigate the internal tide generation mechanism and its impact on ocean mixing in this region1

Comparison of measurements from pressure-recording inverted echo sounders and satellite altimetry in the North Equatorial Current region

Satellite-measured along-track and gridded sea surface height (SSH) anomaly products from AVISO are compared with in situ SSH anomaly measurements from an array of 4 pressure-recording inverted echo sounders (PIESs), which was deployed across the North Equatorial Current in the Western Pacific. PIESs measure bottom pressure (Pbot) and round-trip acoustic travel time from the sea floor to the sea surface (τ). The Pbot and τ measurements are used to estimate, respectively, the mass-loading and steric height variation in SSH anomaly. From Pbot and τ, it is revealed that the mass-loading component is relatively small in this region. Two sets of delayed-time SSH anomaly AVISO products are evaluated: (1) mono-mission Jason-2 along-track product with 9.92-day interval, and (2) “Reference” gridded products with 7-day interval using two satellites sampling from Jason-2 and Cryosat-2. Satellite-measured SSH anomaly, the variation of which is caused by westward-propagating mesoscale eddies and frontal fluctuations bordering subtropical- and tropical-gyres, agrees well with PIES-derived SSH anomaly. Our results confirm that satellite-measured SSH represents well the mesoscale physical processes around the North Equatorial Current.ss the North Equatorial Current in the Western Pacific. PIESs measure bottom pressure (Pbot) and round-trip acoustic travel time from the sea floor to the sea surface (τ). The Pbot and τ measurements are used to estimate, respectively, the mass-loading and steric height variation in SSH anomaly. From Pbot and τ, it is revealed that the mass-loading component is relatively small in this region. Two sets of delayed-time SSH anomaly AVISO products are evaluated: (1) mono-mission Jason-2 along-track product with 9.92-day interval, and (2) “Reference” gridded products with 7-day interval using two satellites sampling from Jason-2 and Cryosat-2. Satellite-measured SSH anomaly, the variation of which is caused by westward-propagating mesoscale eddies and frontal fluctuations bordering subtropical- and tropical-gyres, agrees well with PIES-derived SSH anomaly. Our results confirm that satellite-measured SSH represents well the mesoscale physical processes around the North Equatorial Current.1

Observation and simulation of Internal tides near a potential offshore storage site in the East Sea

Internal tides near the continental slope of the southwestern East Sea were investigated using two sets of 25 hours long hourly CTD and LADCP profiles obtained during spring and neap tidal periods. The profiles span the whole water column from the surface to about 260 m. Semi-diurnal internal tide was the strongest below the main thermocline (150─200 m) where 5ºC isotherm was displaced more than 50 m were observed. The Richardson numbers were low (0─0.25) in layers where large vertical displacements were observed, suggesting internal tide induced mixing. Numerical simulations using an idealized vertical 2.5-dimensional numerical model based on the ROMS reveal that semi-diurnal internal tide was dominantly generated on the continental slope. Simulations using different configurations were conducted for further understanding of internal tide generation mechanism and its impact on ocean mixing in this regionmn from the surface to about 260 m. Semi-diurnal internal tide was the strongest below the main thermocline (150─200 m) where 5ºC isotherm was displaced more than 50 m were observed. The Richardson numbers were low (0─0.25) in layers where large vertical displacements were observed, suggesting internal tide induced mixing. Numerical simulations using an idealized vertical 2.5-dimensional numerical model based on the ROMS reveal that semi-diurnal internal tide was dominantly generated on the continental slope. Simulations using different configurations were conducted for further understanding of internal tide generation mechanism and its impact on ocean mixing in this region2

현장관측과 자료동화 모형의 동중국해 쿠로시오 변동성 비교 분석

대양에서 한반도 지역해로 열, 염 및 물질 수송에 중요한 역할을 하는 쿠로시오의 상류역에서 현장관측을 수행하였다. 2015년 6월과 2016년 6월에 쿠로시오를 가로지르는 단면에서 CTD관측을 수행하였고, 2015년 6월부터 1년간 쿠로시오의 중심축과 그 주변의 유속시계열을 획득하였다. 이를 HYCOM (HYbrid Corrdinate Ocean Model)모형과 한국해양과학기술원에서 개발한 북서태평양 자료동화 모형 NWP_OPS (North Pacific Ocean Prediction System)결과와 비교 분석하였다. 수온, 염분단면 비교 결과 두 모형은 현장관측에서 보이는 수온, 염분의 전반적인 분포를 유사하게 모의하는 것으로 보인다. 하지만 HYCOM은 표층의 수온을 높게 모의한 반면 NWP_OPS는 중층의 수온을 낮게 모의하는 것으로 나타났다. 염분의 경우, 두 모형 모두 표층과 중층에서 현장관측보다 낮게 모의 하는 것으로 나타났다. 한편, 쿠로시오 주축의 유속 분포나 시간변동성은 HYCOM이 NWP_OPS에 비해 현장관측과 비교적 유사하게 모의하였다. 그러나 두 모형 모두 쿠로시오 주축의 유속에 비해 주변의 유속은 잘 모의하지 못한다.2

Observation and simulation of internal tides on the continental slope of the southwestern East Sea

Internal tides near the continental slope of the southwestern East Sea are investigated using two sets of 25-hour-long hourly CTD and LADCP profiles obtained during spring and neap tidal periods. The profiles span the whole water column from the surface to about 260 m. Semi-diurnal internal tide is strongest below the main thermocline (150&#8722 200 m) where the isotherm displacement is more than 50 m. The low Richardson numbers (0-0.25) found below the thermocline imply that internal tidal waves with large vertical displacement of the water column could be one of the major turbulent mixing energy sources in this continental slope region. Numerical simulations using an idealized vertical 2.5-dimensional numerical model using the ROMS reveal that semi-diurnal internal tides are generated near the observation site. from the surface to about 260 m. Semi-diurnal internal tide is strongest below the main thermocline (150&#8722 200 m) where the isotherm displacement is more than 50 m. The low Richardson numbers (0-0.25) found below the thermocline imply that internal tidal waves with large vertical displacement of the water column could be one of the major turbulent mixing energy sources in this continental slope region. Numerical simulations using an idealized vertical 2.5-dimensional numerical model using the ROMS reveal that semi-diurnal internal tides are generated near the observation site.1