Journal of Marine Science and Engineering

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3 pages, 179 KiB

Open AccessEditorial

Oceanic Internal Waves and Internal Tides in the East Asian Marginal Seas

by Sunghyun Nam and Xueen Chen

J. Mar. Sci. Eng. 2022, 10(5), 573; https://doi.org/10.3390/jmse10050573 - 23 Apr 2022

Cited by 1 | Viewed by 1570

Abstract

Inertia-gravity waves or internal waves (IWs) are ubiquitous in the stratified, rotating ocean [...] Full article

(This article belongs to the Special Issue Oceanic Internal Waves and Internal Tides in the East Asian Marginal Seas)

Research

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13 pages, 3838 KiB

Open AccessArticle

Noise of Internal Solitary Waves Measured by Mooring-Mounted Hydrophone Array in the South China Sea

by Jiemeihui Li, Yang Shi, Yixin Yang and Xiaodong Huang

J. Mar. Sci. Eng. 2022, 10(2), 222; https://doi.org/10.3390/jmse10020222 - 08 Feb 2022

Cited by 3 | Viewed by 1840

Abstract

Internal solitary waves in the South China Sea have attracted attention because of their large amplitude and high rate of occurrence. Internal solitary waves have a substantial influence on underwater sound propagation and ambient noise. However, there have seldom been reports on the [...] Read more.

Internal solitary waves in the South China Sea have attracted attention because of their large amplitude and high rate of occurrence. Internal solitary waves have a substantial influence on underwater sound propagation and ambient noise. However, there have seldom been reports on the noise they cause. In this paper, we conducted an internal solitary waves cooperative observation experiment in the South China Sea in 2016. We analyzed the temperature, flow velocity and noise changes induced by internal solitary waves. The power spectra of noise generated by internal solitary waves at frequencies below 100 Hz was almost 20 dB higher than ambient noise. The observed low-frequency noise had uniform harmonics. Combined with the changes of flow velocity, we interpreted the low frequency noise as flow noise induced by vortex-induced vibration of internal solitary waves flowing past the cable mooring system. The noise spectra were related to the position of the cable where the hydrophone was mounted. The closer they were to the middle of the cable, the greater the vibration amplitude, and the stronger the noise. This study provided a passive acoustic monitoring and warning method for high marine currents. Full article

(This article belongs to the Special Issue Oceanic Internal Waves and Internal Tides in the East Asian Marginal Seas)

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12 pages, 35566 KiB

Open AccessArticle

Internal Solitary Wave Activities near the Indonesian Submarine Wreck Site Inferred from Satellite Images

by Tongxin Wang, Xiaodong Huang, Wei Zhao, Shihao Zheng, Yunchao Yang and Jiwei Tian

J. Mar. Sci. Eng. 2022, 10(2), 197; https://doi.org/10.3390/jmse10020197 - 01 Feb 2022

Cited by 11 | Viewed by 2429

Abstract

In the early morning of 21 April 2021 local time, the Indonesian Navy submarine KRI nanggala-402 crashed in the Bali Sea (BS). As internal solitary waves (ISWs) are a great threat to submarine navigation, this paper analyzes the characteristics of ISWs in the [...] Read more.

In the early morning of 21 April 2021 local time, the Indonesian Navy submarine KRI nanggala-402 crashed in the Bali Sea (BS). As internal solitary waves (ISWs) are a great threat to submarine navigation, this paper analyzes the characteristics of ISWs in the BS by surveying satellite remote sensing images collected from 12–21 April 2021. The satellite images revealed active ISWs in the BS near the submarine wreck site with crest lengths approaching 200 km. Originating from the Lombok Strait (LS), the waves travelled northwestward across the BS deep basin, passed through the submarine wreck site, and shoaled onto the continental shelf west of the Kangean Islands, during which process, the propagation speed reached 2.69 m/s in the deep basin and 0.71 m/s in the shallow water. Based on the satellite images, the wave amplitude near the wreck site was reconstructed to be 41 m, and the reconstructed underwater wave structure showed a maximum vertical velocity of 10 cm/s. Satellite images also demonstrated the near-source evidence of ISWs near the Nusa Penida sill of the LS, and their generation were estimated to be related to the southward tidal current troughs. Full article

(This article belongs to the Special Issue Oceanic Internal Waves and Internal Tides in the East Asian Marginal Seas)

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8 pages, 5578 KiB

Open AccessArticle

Distribution and Source Sites of Nonlinear Internal Waves Northeast of Hainan Island

by Jianjun Liang, Xiao-Ming Li and Kaiguo Fan

J. Mar. Sci. Eng. 2022, 10(1), 55; https://doi.org/10.3390/jmse10010055 - 04 Jan 2022

Cited by 2 | Viewed by 1413

Abstract

The distribution and source sites of nonlinear internal waves (NLIWs) northeast of Hainan Island were investigated using satellite observations and a wavefront propagation model. Satellite observations show two types of NLIWs (here referred to as type-S and type-D waves). The type-S waves are [...] Read more.

The distribution and source sites of nonlinear internal waves (NLIWs) northeast of Hainan Island were investigated using satellite observations and a wavefront propagation model. Satellite observations show two types of NLIWs (here referred to as type-S and type-D waves). The type-S waves are spaced at a semidiurnal tidal period and the type-D waves are spaced at a diurnal tidal period. The spatial distribution of the two types of NLIWs displays a sandwich structure in which the middle region is influenced by both types of NLIWs, and the northern and southern regions are governed by the type-S and type-D waves, respectively. Solving the wavefront model yields good agreement between simulated and observed wavefronts from the Luzon Strait to Hainan Island. We conclude that the NLIWs originate from the Luzon Strait. Full article

(This article belongs to the Special Issue Oceanic Internal Waves and Internal Tides in the East Asian Marginal Seas)

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19 pages, 4169 KiB

Open AccessArticle

Nonseasonal Variations in Near-Inertial Kinetic Energy Observed Far below the Surface Mixed Layer in the Southwestern East Sea (Japan Sea)

by Suyun Noh and SungHyun Nam

J. Mar. Sci. Eng. 2022, 10(1), 9; https://doi.org/10.3390/jmse10010009 - 23 Dec 2021

Cited by 2 | Viewed by 2894

Abstract

Near-inertial internal waves (NIWs) generated by surface wind forcing are intermittently enhanced below and within the surface mixed layer. The NIW kinetic energy below the surface mixed layer varies over intraseasonal, interannual, and decadal timescales; however, these variations remain unexplored, due to a [...] Read more.

Near-inertial internal waves (NIWs) generated by surface wind forcing are intermittently enhanced below and within the surface mixed layer. The NIW kinetic energy below the surface mixed layer varies over intraseasonal, interannual, and decadal timescales; however, these variations remain unexplored, due to a lack of long-term, in situ observations. We present statistical results on the nonseasonal variability of the NIW kinetic energy 400 m below the surface mixed layer in the southwestern East Sea, using moored current measurements from 21 years. We used long time series of the near-inertial band (0.85–1.15 f) kinetic energy to define nine periods of relatively high (period high) and seven periods of relatively low (period low) NIW kinetic energy. The NIW kinetic energy average at period high was about 24 times higher than that at period low and those in specific years (2003, 2012–2013, 2016, and 2020) and decade (2010s) were significantly higher than those in other years and decade (2000s). Composite analysis revealed that negative relative vorticity and strong total strain significantly enhance NIW kinetic energy at 400 m. The relative vorticity was negative (total strain was positively enhanced) during seven (six) out of nine events of period high. NIW trapping in a region of negative relative vorticity and the wave capture process induce nonseasonal variations in NIW kinetic energy below the surface mixed layer. Our study reveals that, over intraseasonal, interannual, and decadal timescales, mesoscale flow fields significantly influence NIWs. Full article

(This article belongs to the Special Issue Oceanic Internal Waves and Internal Tides in the East Asian Marginal Seas)

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10 pages, 5226 KiB

Open AccessArticle

A Strong Internal Solitary Wave with Extreme Velocity Captured Northeast of Dong-Sha Atoll in the Northern South China Sea

by Andi Xu and Xueen Chen

J. Mar. Sci. Eng. 2021, 9(11), 1277; https://doi.org/10.3390/jmse9111277 - 17 Nov 2021

Cited by 6 | Viewed by 1896

Abstract

Internal solitary waves (ISWs) in the South China Sea (SCS) have received considerable attention. This paper reports on a strong ISW captured northeast of Dong-Sha Atoll on 22 May 2011 by shipboard Acoustic Doppler Current Profiler (ADCP), which had the largest velocity among [...] Read more.

Internal solitary waves (ISWs) in the South China Sea (SCS) have received considerable attention. This paper reports on a strong ISW captured northeast of Dong-Sha Atoll on 22 May 2011 by shipboard Acoustic Doppler Current Profiler (ADCP), which had the largest velocity among the ISWs so far reported in the global ocean. The peak westward velocity (u) was 2.94 m/s, and the peak downward velocity (w) was 0.63 m/s, indicating a first baroclinic mode depression wave. The amplitude of ISW inferred from ADCP backscatter was about 97 m. 2.2 h later, a trailing wave was captured with a peak westward velocity and downward velocity of 2.24 m/s and 0.42 m/s, respectively, surprisingly large for a trailing wave, suggesting that the ISW is type-A wave. The estimated baroclinic current induced by the leading ISW was much larger than the barotropic current. The Korteweg-De Vries (KdV) theoretical phase speed and the phase speed inferred from the satellite images were 1.76 m/s and 1.59 m/s, respectively. The peak horizontal velocity exceeded the phase speed, suggesting the ISW was close to or already in the process of breaking and may have formed a trapped core. Full article

(This article belongs to the Special Issue Oceanic Internal Waves and Internal Tides in the East Asian Marginal Seas)

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16 pages, 5265 KiB

Open AccessArticle

Estimation of Propagation Speed and Direction of Nonlinear Internal Waves from Underway and Moored Measurements

by Seung-Woo Lee and Sunghyun Nam

J. Mar. Sci. Eng. 2021, 9(10), 1089; https://doi.org/10.3390/jmse9101089 - 06 Oct 2021

Cited by 2 | Viewed by 1811

Abstract

Propagation speed and direction of nonlinear internal waves (NLIWs) are important parameters for understanding the generation and propagation of waves, and ultimately clarifying regional ocean circulation. However, these parameters cannot be directly measured from in-situ instruments, but can only be estimated from post-processing [...] Read more.

Propagation speed and direction of nonlinear internal waves (NLIWs) are important parameters for understanding the generation and propagation of waves, and ultimately clarifying regional ocean circulation. However, these parameters cannot be directly measured from in-situ instruments, but can only be estimated from post-processing in situ data. Herein, we present two methods and an optimal approach to estimate the propagation speed and direction of waves using underway and moored observations. The Doppler shift method estimates these parameters from apparent observations concerning a moving ship using the Doppler shift induced by the changing relative distance of the NLIWs from the moving ship. The time lag method estimates the parameters using the distance between two locations of the NLIW observed at different times and the time lag. To optimize the speed and direction of NLIWs, the difference in the propagation direction independently estimated by the two methods needs to be minimized concerning the optimal propagation speed to yield the optimal propagation direction. The methods were applied to two cases observed in the northern East China Sea in May 2015 and August 2018. This study has practical significance for better estimating the propagation speed and direction of NILWs particularly over a broad continental shelf. Full article

(This article belongs to the Special Issue Oceanic Internal Waves and Internal Tides in the East Asian Marginal Seas)

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16 pages, 6078 KiB

Open AccessArticle

The Impact of Fortnightly Stratification Variability on the Generation of Baroclinic Tides in the Luzon Strait

by Zheen Zhang, Xueen Chen and Thomas Pohlmann

J. Mar. Sci. Eng. 2021, 9(7), 703; https://doi.org/10.3390/jmse9070703 - 26 Jun 2021

Cited by 1 | Viewed by 1759

Abstract

The impact of fortnightly stratification variability induced by tide–topography interaction on the generation of baroclinic tides in the Luzon Strait is numerically investigated using the MIT general circulation model. The simulation shows that advection of buoyancy by baroclinic flows results in daily oscillations [...] Read more.

The impact of fortnightly stratification variability induced by tide–topography interaction on the generation of baroclinic tides in the Luzon Strait is numerically investigated using the MIT general circulation model. The simulation shows that advection of buoyancy by baroclinic flows results in daily oscillations and a fortnightly variability in the stratification at the main generation site of internal tides. As the stratification for the whole Luzon Strait is periodically redistributed by these flows, the energy analysis indicates that the fortnightly stratification variability can significantly affect the energy transfer between barotropic and baroclinic tides. Due to this effect on stratification variability by the baroclinic flows, the phases of baroclinic potential energy variability do not match the phase of barotropic forcing in the fortnight time scale. This phenomenon leads to the fact that the maximum baroclinic tides may not be generated during the maximum barotropic forcing. Therefore, a significant impact of stratification variability on the generation of baroclinic tides is demonstrated by our modeling study, which suggests a lead–lag relation between barotropic tidal forcing and maximum baroclinic response in the Luzon Strait within the fortnightly tidal cycle. Full article

(This article belongs to the Special Issue Oceanic Internal Waves and Internal Tides in the East Asian Marginal Seas)

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15 pages, 6288 KiB

Open AccessArticle

Near-Inertial Waves Induced by Typhoon Megi (2010) in the South China Sea

by Anzhou Cao, Zheng Guo, Yunhe Pan, Jinbao Song, Hailun He and Peiliang Li

J. Mar. Sci. Eng. 2021, 9(4), 440; https://doi.org/10.3390/jmse9040440 - 18 Apr 2021

Cited by 18 | Viewed by 2728

Abstract

Near-inertial waves (NIWs) are a kind of internal wave, which are usually generated by synoptic wind forcing and play an important role in the oceanic energy budget. However, the lack of in situ observations limits our understanding of NIWs to some extent. Through [...] Read more.

Near-inertial waves (NIWs) are a kind of internal wave, which are usually generated by synoptic wind forcing and play an important role in the oceanic energy budget. However, the lack of in situ observations limits our understanding of NIWs to some extent. Through a comparison with in situ observations, in this study, we first showed that the hybrid coordinate ocean model reanalysis results could reasonably reproduce the typhoon-induced NIWs, and we then adopted these data to investigate the NIWs induced by typhoon Megi in 2010 in the South China Sea (SCS). The results indicate that Megi-induced near-inertial kinetic energy was mainly concentrated in the SCS Basin. In the vertical direction, Megi-induced NIWs could propagate to 1000 m depth. The damping and modal content of Megi-induced NIWs were site-dependent: In the region near Megi’s track, NIWs were dominated by the first three baroclinic modes and damped quickly; whereas in two zones to the west of the Luzon Island and Luzon Strait, the e-folding time of Megi-induced NIWs could be longer than 20 days and higher modes (mode-4 to mode-7) were enhanced several days after the passage of Megi. Possible mechanisms of these phenomena were also explored in this study. Full article

(This article belongs to the Special Issue Oceanic Internal Waves and Internal Tides in the East Asian Marginal Seas)

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