Research

12 pages, 15633 KiB

Open AccessArticle

Evaluating the Detection of Oceanic Mesoscale Eddies in an Operational Eddy-Resolving Global Forecasting System

by Huier Mo, Yinghao Qin, Liying Wan, Yu Zhang, Xing Huang, Yi Wang, Jianyong Xing, Qinglong Yu and Xiangyu Wu

J. Mar. Sci. Eng. 2023, 11(12), 2343; https://doi.org/10.3390/jmse11122343 - 12 Dec 2023

Viewed by 662

Abstract

In this study, a global analysis and forecasting system at 1/12° is built for operational oceanography at the National Marine Environmental Forecasting Center (NMEFC) by using the NEMO ocean model (NMEFC-NEMO). First, statistical analysis methods are designed to evaluate the performance of sea [...] Read more.

In this study, a global analysis and forecasting system at 1/12° is built for operational oceanography at the National Marine Environmental Forecasting Center (NMEFC) by using the NEMO ocean model (NMEFC-NEMO). First, statistical analysis methods are designed to evaluate the performance of sea level anomaly (SLA) forecasting. The results indicate that the NMEFC-NEMO performs well in SLA forecasting when compared with the Mercator-PSY4, Mercator-PSY3, UK-FOAM, CONCEPTS-GIOPS and Bluelink-OceanMAPS forecasting systems. The respective root-mean-squared errors (RMSEs) of NMEFC-NEMO (Mercator PSY4) are 0.0654 m (0.0663 m) and 0.0797 m (0.0767 m) for the lead times of 1 and 7 days. The anomaly correlation coefficients between forecasting and observations exceed 0.8 for the NMEFC-NEMO and Mercator-PSY4 systems, suggesting that the accuracy of SLA predicted using NMEFC-NEMO is comparable to Mercator PSY4 and superior to other forecasting systems. Moreover, the global spatial distribution of oceanic eddies are effectively represented in NMEFC-NEMO when compared to that in the HYCOM reanalysis, and the detection rate reaches more than 90% relative to HYCOM reanalysis. Regarding the strong eddies in the Kuroshio region, the NMEFC-NEMO reproduces the characteristic for anticyclonic and cyclonic eddies merging and splitting alternatively. As for the detective eddies in the Gulf Stream, NMEFC-NEMO effectively represents the spatial distribution of mesoscale eddies from different seasons. The amplitude of oceanic eddies, including both cyclones and anticyclones, were much stronger on 1 July 2019 than 1 January 2019. Overall, NMEFC-NEMO has a superior performance in SLA forecasting and effectively represents the oceanic mesoscale eddies for operational oceanography. Full article

(This article belongs to the Special Issue Advance in Circulation and Internal Wave Dynamics)

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14 pages, 2990 KiB

Open AccessArticle

Experimental Investigation on the Vertical Structure Characteristics of Internal Solitary Waves

by Pai Peng, Hui Du, Gang Wei, Shaodong Wang, Pu Xuan, Shuqun Cai and Jieshuo Xie

J. Mar. Sci. Eng. 2022, 10(8), 1045; https://doi.org/10.3390/jmse10081045 - 29 Jul 2022

Cited by 3 | Viewed by 1395

Abstract

An experimental investigation of the vertical structure characteristics of internal solitary waves (ISWs) was systematically carried out in a large gravitationally stratified fluid flume. Four different stratifications were established, and basic elements of ISWs were measured by a conductivity probe array. The vertical [...] Read more.

An experimental investigation of the vertical structure characteristics of internal solitary waves (ISWs) was systematically carried out in a large gravitationally stratified fluid flume. Four different stratifications were established, and basic elements of ISWs were measured by a conductivity probe array. The vertical distributions of the amplitude, characteristic frequency and waveform of two types of ISWs under different stratifications were obtained, and the experimental results were compared with the theoretical model. The study shows that most vertical structures of the amplitude under different stratifications agree with those of the theoretical model, while there are some deviations for ISWs with large amplitudes. Neither the two-layer model nor the continuously stratified model can effectively describe the variation in the characteristic frequency at different depths with amplitude. For a single small-amplitude ISW, the characteristic frequency first increases and then decreases with increasing depth. The characteristic frequency is largest at the depth of the maximum buoyancy frequency. For an ISW with a relatively large amplitude, there is likely to be a local minimum of the characteristic frequency near the depth where the maximum buoyancy frequency lies. In different stratifications, the

{sech}^{2}

function of KdV theory can describe the waveforms of ISWs at different depths well. Full article

(This article belongs to the Special Issue Advance in Circulation and Internal Wave Dynamics)

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14 pages, 6457 KiB

Open AccessArticle

Lagrangian Observation of the Kuroshio Current by Surface Drifters in 2019

by Zhenyu Sun, Jianyu Hu, Hongyang Lin, Zhaozhang Chen, Jia Zhu, Longqi Yang, Zhiyuan Hu, Xirong Chen and Xuewen Wu

J. Mar. Sci. Eng. 2022, 10(8), 1027; https://doi.org/10.3390/jmse10081027 - 26 Jul 2022

Cited by 5 | Viewed by 1901

Abstract

In this research, the features of the Kuroshio Current in 2019 were studied based on the observations of 29 self-developed surface current experiment drifters deployed in the western Pacific Ocean and the East China Sea. The Kuroshio flow pattern and velocity magnitude observed [...] Read more.

In this research, the features of the Kuroshio Current in 2019 were studied based on the observations of 29 self-developed surface current experiment drifters deployed in the western Pacific Ocean and the East China Sea. The Kuroshio flow pattern and velocity magnitude observed in 2019 were largely consistent with the climatology based on the historical drifter dataset, but they still exhibited distinctive characteristics. The intrusion of the Kuroshio into the South China Sea in the spring was observed by a group of drifters crossing the Luzon Strait from east to west, which is a notable departure from the non-intrusion pattern noted to occur in the spring in most of the historical records. A strong intrusion of the Kuroshio into the East China Sea was also observed, taking an anti-cyclonic turn in the northeast of Taiwan Island. Both the drifter trajectories and altimeter-derived dynamical topography captured the large meander pattern of the Kuroshio south of Japan in 2019, with the flow path having a maximum offshore distance of 470 km. In addition, Lagrangian statistics (lateral diffusivity, integral time scale, and integral space scale) were estimated for four selected regions with adequate drifter samplings. The lateral diffusivity had large values along the Kuroshio segment in the East China Sea and small values on the continental shelf of the East China Sea. The integral time scales for the four regions ranged from 0.8 to 3.7 days, with a corresponding integral space scale of 19~128 km. Full article

(This article belongs to the Special Issue Advance in Circulation and Internal Wave Dynamics)

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14 pages, 2732 KiB

Open AccessArticle

Observational Analysis of the Formation Reasons and Evolution Law of Winter Counter-Wind Current in Jiazi Sea Area of Northeastern South China Sea

by Yizhan Chen, Yonggang Cao, Shizhi Liao, Yuan Ma, Yuqiang Liu, Yongzhong Ouyang and Rong Xiang

J. Mar. Sci. Eng. 2022, 10(7), 893; https://doi.org/10.3390/jmse10070893 - 28 Jun 2022

Cited by 1 | Viewed by 1118

Abstract

Based on the observational data of wind, current, and sea surface temperature in the Jiazi sea area of the northeastern South China Sea in 2018 and the satellite remote sensing data of sea surface temperature in the northern South China Sea, this paper [...] Read more.

Based on the observational data of wind, current, and sea surface temperature in the Jiazi sea area of the northeastern South China Sea in 2018 and the satellite remote sensing data of sea surface temperature in the northern South China Sea, this paper explores the formation reasons and evolution law of winter counter-wind currents in the Jiazi sea area of the northeastern South China Sea. The results show that: (1) The counter-wind current in the Jiazi sea occurs only in certain time periods instead of the entire winter; (2) When the eastern component of wind stress weakens, the eastern component of seafloor friction also weakens to some extent. A high-frequency northeast current often occurs in the bottom layer of the sea area, indicating that the formation of winter counter-wind current in the Jiazi sea area is a result of the concerted action of wind stress, the baroclinic effect, and geostrophic effect; (3) When the counter-wind current is formed, there is a low temperature water mass in the northwest of Jiazi and a high-temperature water mass in the southeast. The baroclinic effect causes the sea water to flow to the shore and produce a westward flow on the shore, and northeastward counter-wind current occurs on convergent sea water on the shore due to the baroclinic effect and geostrophic effect (Ekman effect). Therefore, two different current systems are formed in the northeastern South China Sea in winter with 116° E as the boundary. The appearance of cold water masses in the northwest of 116° E sea area and warm water masses in the southeast of the South China Sea is the key to the formation of both the two different current systems with 116° E as the boundary and the winter counter-wind flow; (4) The formation and disappearance of the counter-wind current can be divided into four stages: in the first stage, the northeast monsoon gradually relaxes to become the southeast wind, forming the northwest current; in the second stage, the warm water masses on the west side of the Luzon Strait flow to the coastal waters due to the northwest current, forming a significant onshore pressure gradient force; in the third stage, a high-temperature seawater convergence zone is formed in the Jiazi sea area, forming southwest and northeast pressure gradient forces, and the northwest coastal current forms a counter-wind current under the combined action of pressure gradient force and geostrophic effect; in the fourth stage, the northeast monsoon intensifies and the counter-wind current weakens gradually until it disappears, and the sea water flows to the southwest again. Full article

(This article belongs to the Special Issue Advance in Circulation and Internal Wave Dynamics)

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16 pages, 6957 KiB

Open AccessArticle

Climatic Change of Summer Wind Direction and Its Impact on Hydrodynamic Circulation in the Pearl River Estuary

by Bo Hong, Hanlu Xue, Liangsheng Zhu and Hongzhou Xu

J. Mar. Sci. Eng. 2022, 10(7), 842; https://doi.org/10.3390/jmse10070842 - 21 Jun 2022

Cited by 5 | Viewed by 1918

Abstract

Assessing the trend of sea surface wind is important for understanding the response of the marine environment to climate change. Analysis of wind data reveals that the summer wind direction in the Pearl River Estuary (PRE) shifts anticlockwise at a rate of −0.36°yr [...] Read more.

Assessing the trend of sea surface wind is important for understanding the response of the marine environment to climate change. Analysis of wind data reveals that the summer wind direction in the Pearl River Estuary (PRE) shifts anticlockwise at a rate of −0.36°yr⁻¹ over the past 42 years (1979–2020). The mean wind direction in July shifts from 183.6° (in 1979) to 169.3° (in 2020) and is predicted as 142.1° by 2100. How this long-term wind direction change affects the PRE hydrodynamic circulation structure has not been examined yet. A fully calibrated high resolution 3D hydrodynamic model is used to evaluate the response of local hydrodynamics to wind direction shifting in this study. The model results indicate that both the cross-channel wind-driven transport and along-channel seaward flow are weakened as wind direction shifts. Consequently, the lateral circulation is slowed down significantly while the longitudinal exchange flow is weakened slightly. A remarkable increase in stratification occurs in the coastal sea adjacent to the Modaomen where hypoxia has been frequently reported. The residence time of Lingding Bay increases slightly. The Momentum budget indicates the wind direction shifting can cause major changes in the barotropic pressure term, which is mainly balanced by the baroclinic pressure term and diffusion term. Full article

(This article belongs to the Special Issue Advance in Circulation and Internal Wave Dynamics)

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15 pages, 5030 KiB

Open AccessArticle

Observations of Reflected Internal Solitary Waves near the Continental Shelf of the Dongsha Atoll

by Hao Zhang, Junmin Meng, Lina Sun and Shibao Li

J. Mar. Sci. Eng. 2022, 10(6), 763; https://doi.org/10.3390/jmse10060763 - 31 May 2022

Cited by 2 | Viewed by 1412

Abstract

Internal solitary waves (ISWs) near the Dongsha Atoll in the northern South China Sea (SCS) can be divided into incident, reflected, and refracted waves. Compared with the incident and refracted ISWs, the reflected ISWs are less likely to appear, but their impact on [...] Read more.

Internal solitary waves (ISWs) near the Dongsha Atoll in the northern South China Sea (SCS) can be divided into incident, reflected, and refracted waves. Compared with the incident and refracted ISWs, the reflected ISWs are less likely to appear, but their impact on the ecological environment and marine activity should not be underestimated. In this work, field experiments were performed and moderate-resolution imaging spectroradiometer (MODIS) images were collected to analyze the reflected ISWs. Satellite observations showed that they were excited by the collision between the incident ISWs and the Dongsha Atoll and are often in the form of a wave packet composed of 2 to 5 solitons. During propagation, its spatial range gradually increases and interacts with the incoming waves generated by the next tidal cycle until it dissipates at approximately 117.5° E. Eighty percent of the reflected ISWs occur from April to June. The length of the crest line is mainly between 50 and 150 km, and the average propagation speed is approximately 1.57 m/s, which is smaller than that of the incident ISWs. In situ observations showed that the amplitudes of the reflected ISWs were between 10 and 20 m, accounting for only 40% of the incident ISWs. Compared with the incident ISWs, the vertical, velocity, and zonal velocities of the reflected ISWs were all attenuated. The results of the depth-integrated horizontal energy flux calculation showed that the energy of the reflected ISWs was only 61% of that of the incident ISWs. The reflected ISWs accelerated the velocity of the surface flow field during propagation, and the maximum velocity on the sea surface was approximately 0.60 m/s. Strong tides are beneficial for the generation of reflected ISWs near the Dongsha Atoll. Incident and reflected ISWs are all first-mode ISWs. Full article

(This article belongs to the Special Issue Advance in Circulation and Internal Wave Dynamics)

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15 pages, 11544 KiB

Open AccessArticle

On the Response of Zhejiang Coastal Waters to 12 Typhoons from 2011 to 2015

by Yunhe Pan, Anzhou Cao, Yuqian Wu, Shiming Lu, Luteng Fan and Peiliang Li

J. Mar. Sci. Eng. 2022, 10(4), 543; https://doi.org/10.3390/jmse10040543 - 14 Apr 2022

Cited by 1 | Viewed by 1539

Abstract

Based on the hybrid coordinate ocean model (HYCOM) reanalysis data, the dynamical and thermal response of Zhejiang coastal waters to 12 typhoons from 2011 to 2015 was studied, and the relationship between the oceanic response and typhoon characteristics was analyzed. The HYCOM reanalysis [...] Read more.

Based on the hybrid coordinate ocean model (HYCOM) reanalysis data, the dynamical and thermal response of Zhejiang coastal waters to 12 typhoons from 2011 to 2015 was studied, and the relationship between the oceanic response and typhoon characteristics was analyzed. The HYCOM reanalysis data were validated by satellite-observed sea surface temperature data. Results show that all the 12 typhoons caused near-inertial waves, sea surface cooling and seafloor warming, but significant differences existed among them. Based on statistics, it was found that the domain-averaged near-inertial kinetic energy and seafloor warming are significantly correlated with the typhoon’s maximum wind speed, both of which show a positive relationship. The domain-averaged seafloor warming also decreases with the typhoon’s translation speed. Moreover, there exists a positive correlation between the domain-averaged sea surface cooling and seafloor warming. The different mechanisms that caused the seafloor warming for the 12 typhoons were also investigated in this study. Full article

(This article belongs to the Special Issue Advance in Circulation and Internal Wave Dynamics)

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21 pages, 9064 KiB

Open AccessArticle

Model Simulation of M₂ Internal Tide at the Mariana Double Ridges

by Qi’an Chen, Liu Yu, Qingxuan Yang, Philip Adam Vetter, Hongzhou Xu, Qiang Xie, Huichang Jiang and Zekai Ni

J. Mar. Sci. Eng. 2021, 9(6), 592; https://doi.org/10.3390/jmse9060592 - 29 May 2021

Cited by 1 | Viewed by 2056

Abstract

In this study, M₂ tidal energy and tide-induced mixing in the Mariana double ridges are investigated with a high-resolution three-dimensional non-hydrostatic numerical model and baroclinic energy budget analysis. The interference effect of the double ridges on the internal tide in the Mariana [...] Read more.

In this study, M₂ tidal energy and tide-induced mixing in the Mariana double ridges are investigated with a high-resolution three-dimensional non-hydrostatic numerical model and baroclinic energy budget analysis. The interference effect of the double ridges on the internal tide in the Mariana is examined by omitting either the eastern or the western ridge. Our results show that the baroclinic velocity on the sides of the interior facing slopes of the double ridges is larger than that on the other sides. In the double ridges, high values of dissipation reaching O (10⁻⁶ W kg⁻¹) are accompanied by diapycnal diffusivity reaching O (10⁻¹ m² s⁻¹), which is several orders of magnitude higher than the mixing of the open ocean. The bottom diapycnal mixing in the inner region between the two ridges is one order of magnitude larger than the mixing outside the ridges, indicating the important role of the interference of the double-ridge topography on the mixing in the Mariana Arc. Omitting either the eastern or the western ridge would have a significant impact on tide current, baroclinic energy flux and dissipation, and diapycnal mixing. The internal tide conversion, dissipation, and flux divergence are amplified by the double ridge topography, especially in the central part of the double ridges. Through energy budgets analysis, we conclude that the eastern ridge is the main source of the baroclinic tide in the Mariana double ridges. Full article

(This article belongs to the Special Issue Advance in Circulation and Internal Wave Dynamics)

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