Ocean Surface Currents Research Articles

Numerical simulation study on hydrodynamics of Xisha Islands and Reefs driven by tide levels, sea surface heights and ocean currents

This study employs the FVCOM numerical model to investigate tide flow and hydrodynamics in the marine region surrounding Yongxing Island. The HYCOM model is utilized to obtain sea surface height and ocean current data at the boundary. Additionally, the astronomical tide level predicted by the TPXO9 global tide model is incorporated into the analysis. Through numerical simulation research, the paper aims to examine the aforementioned phenomena. The findings indicate a strong concurrence between the outcomes of the FVCOM numerical simulation and the observed data. The winter and summer tidal patterns in the seas around Yongxing Island exhibit a high degree of similarity. In winter, the current speed of rapid flood and ebb process, exhibits somewhat higher than that in summer. The maximum current speed occurs in the northern marine region of Yongxing Island, during the rapid flood process, whereas it occurs in the northwest marine region of Yongxing Island during the rapid ebb process.

Improved Surface Currents from Altimeter-Derived and Sea Surface Temperature Observations: Application to the North Atlantic Ocean

We present a study on the ocean surface currents reconstruction by merging Level-4 (L4, gap-free) altimeter-derived geostrophic currents and satellite sea surface temperature. Building upon past studies on the multi-variate reconstruction of geostrophic currents from satellite observations, we regionalized and optimized an algorithm to improve the altimeter-derived surface circulation estimates in the North Atlantic Ocean. A ten-year-long time series (2010–2019) is presented and validated by means of in situ observations. The newly optimized algorithm allowed us to improve the currents estimate along the main axis of the Gulf Stream and in correspondence of well-known upwelling areas in the North Eastern Atlantic, with percentage improvements of around 15% compared to standard operational altimetry products.

An investigation of inversion method to measure the radial velocity of Kuroshio from Sentinel-1 SAR data

ABSTRACT Studies on the retrieval of ocean surface current by Synthetic Aperture Radar (SAR) mainly concentrate on coastal regions with land coverage, allowing for continuous land to estimate non-geophysical Doppler shifts. As a strong western boundary in the Western Pacific, the Kuroshio flows through mostly islands or open sea, and lacks land coverage for range bias correction. We propose a non-geophysical Doppler shift correction algorithm suitable for Kuroshio observation. Three solutions matching different land coverage were adopted in the range direction, and the scalloping was removed by using average filtering in the azimuth direction. Comparison between SAR radial velocity and Global Surface Lagrangian Drifter (GLD) reveals that the correlation coefficient (R 2) increase to 0.686, and root mean square error (RMSE) of 0.215 m/s after non-geophysical corrections, while the wind-wave bias corrections make R 2 increase to 0.806 and RMSE decrease to 0.13 m/s. There is also a good consistency between SAR inversion and Regional Ocean Circulation Model (ROMS). Sensitivity analysis illustrates that ascending pass is more suitable for monitoring Kuroshio, and high incidence angles are less affected by ocean conditions and non-geophysical factors. The algorithm can be used in regions with discontinuous or absent land.

A particle tracking model approach to determine the dispersal of riverine plastic debris released into the Indian Ocean

Although the Indian Ocean receives a large amount of land-based plastic waste, the studies on pathways of riverine plastic debris are limited to date. Therefore, a particle tracking model that included ocean surface currents, horizontal diffusion, Stokes drift, windage, and beaching/re-drifting processes was developed to reproduce the behavior of riverine plastic debris in the Indian Ocean. The modeled particles were released in the model domain based on riverine plastic debris database. The maximum abundance of beached particles occurred during the southwesterly monsoon season, particularly in the Bay of Bengal. The particles released from the rivers were trapped in the northern Indian Ocean unless both Stokes drift and windage were excluded from transportation velocity. These results suggest that the riverine plastic debris was trapped in the northern Indian Ocean until it fragmented into less buoyant small microplastics drifting in the subsurface layer, free from windage and Stokes drift at increasing depths.

Pelagic Sargassum in the Gulf of Mexico driven by ocean currents and eddies

Pelagic Sargassum in the Gulf of Mexico (GoM) plays an important role in ocean biology and ecology, yet our knowledge of its origins and transport pathways is limited. Here, using satellite observations of Sargassum areal density and ocean surface currents between 2000 and 2023, we show that large amounts of Sargassum in the GoM can either originate from the northwestern GoM or be a result of physical transport from the northwestern Caribbean Sea, both with specific transport pathways. Sargassum of the northwestern GoM can be transported to the eastern GoM by ocean currents and eddies, eventually entering the Sargasso Sea. Sargassum entering the GoM from the northwestern Caribbean Sea can be transported in three different directions, with the northward and eastward transports governed by the Loop Current System (LCS) and westward transport driven by the westward extension of the LCS, the propagation or relaying of ocean eddies, the wind-driven westward currents on the Campeche Bank with or without eddies, and the westward currents with/without currents associated with eddies in the northern/central GoM. Overall, the spatial distribution patterns of pelagic Sargassum in the GoM are strongly influenced by the LCS and relevant eddies.

The Water-Following Performance of Various Lagrangian Surface Drifters Measured in a Dye Release Experiment

Abstract Many different surface drifter designs have been developed recently to track near-surface ocean currents, but the degree to which these drifters slip through the water because of mechanisms associated with the wind is poorly known. In the 2020 Tracer Release Experiment (TReX), 19 drifters of eight different designs, both commercially available and home-built, were simultaneously released with a patch of rhodamine dye. The dye rapidly spread vertically through the mixed layer but also more slowly dispersed horizontally. Although winds were light, drifters moved downwind from the dye patch at speeds of 3–17 cm s−1 (0.6%–4% of wind speed) depending on the design type. Measurements were made of wind and ocean conditions, and these were incorporated into a boundary layer model at the air–sea interface to estimate complete velocity profiles above and below the surface. Then, a steady-state drag model is used with these profiles to successfully predict drifter slip. Drogued drifters (those with a subsurface drag element) can be affected by Eulerian shear in the upper 0.5 m of the water column, as well as the Stokes drift, but undrogued drifters are in addition greatly affected by direct wind drag, and possibly by resonant interactions with waves. The dye, cycling vertically in the mixed layer, is largely unaffected by all of these factors; therefore, even “perfect” surface drifters do not move with a mixed layer tracer. Significance Statement Surface drifters are used by oceanographers to measure ocean surface currents. However, different designs also slip downwind through the water at rates that are poorly known but are typically around a few percent of the wind speed. In 2020 we simultaneously deployed drifters of eight different designs along with rhodamine dye in a field experiment to see how well the different designs track the water. Here we independently and successfully model drifter slippage for the different designs. Slip factors are then estimated for a range of wind and ocean conditions.

Mapping Radial Ocean Surface Currents in the Outer Core of Hurricane Maria From Synthetic Aperture Radar Doppler Measurements

Mapping Radial Ocean Surface Currents in the Outer Core of Hurricane Maria From Synthetic Aperture Radar Doppler Measurements

Evaluation of Antenna Pattern Measurement of HF Radar using Drone

The High-Frequency Radar (HFR) is an equipment designed to measure real-time surface ocean currents in broad maritime areas.It emits radio waves at a specific frequency (HF) towards the sea surface and analyzes the backscattered waves to measure surface current vectors (Crombie, 1955; Barrick, 1972).The Seasonde HF Radar from Codar, utilized in this study, determines the speed and location of radial currents by analyzing the Bragg peak intensity of transmitted and received waves from an omnidirectional antenna and employing the Multiple Signal Classification (MUSIC) algorithm. The generated currents are initially considered ideal patterns without taking into account the characteristics of the observed electromagnetic wave propagation environment. To correct this, Antenna Pattern Measurement (APM) is performed, measuring the strength of signals at various positions received by the antenna and calculating the corrected measured vector to radial currents.The APM principle involves modifying the position and phase information of the currents based on the measured signal strength at each location. Typically, experiments are conducted by installing an antenna on a ship (Kim et al., 2022). However, using a ship introduces various environmental constraints, such as weather conditions and maritime situations. To reduce dependence on maritime conditions and enhance economic efficiency, this study explores the possibility of using unmanned aerial vehicles (drones) for APM. The research conducted APM experiments using a high-frequency radar installed at Dangsa Lighthouse in Dangsa-ri, Wando County, Jeollanam-do. The study compared and analyzed the results of APM experiments using ships and drones, utilizing the calculated radial currents and surface current fields obtained from each experiment.

ASTMEN: an adaptive spatiotemporal and multi-element fusion network for ocean surface currents forecasting

Accurate forecasting of ocean surface currents is crucial for the planning of marine activities, including fisheries, shipping, and pollution control. Previous studies have often neglected the consideration of spatiotemporal correlations and interdependencies among ocean elements, leading to suboptimal accuracy in medium to long-term forecasts, especially in regions characterized by intricate ocean currents. This paper proposes an adaptive spatiotemporal and multi-element fusion network for ocean surface currents forecasting (ASTMEN). Specifically, we use an improved Swin Transformer (Swin-T) to perform self-attention computation at any given moment, enabling the adaptive generation of multi-element time series with spatial dependencies. Then, we utilize a Long Short-Term Memory network (LSTM) to encode and decode these series in the dimensions of temporal and multi-element features, resulting in accurate forecasts of ocean surface currents. This study takes the Kuroshio region in the northwest Pacific Ocean as the study area with data from the ocean reanalysis dataset. The experimental results show that ASTMEN significantly outperforms the baseline model and the climate state method, and is the only model whose correlation coefficient is still higher than 0.8 at day 12. In the experiments during the summer, when the currents are most variable, ASTMEN provides better forecasts at the sea-land interface and at the junction of different currents, which has the potential to fill the gap of poor forecast performance of previous methods for complex current fields.

Genetic analyses reveal panmixia in Indian waters and population subdivision across Indian Ocean and Indo-Malay Archipelago for Decapterus russelli

The Indian Scad, Decapterus russelli is an important pelagic carangid widely distributed throughout the Indian Ocean and the Indo-West Pacific. Despite being widely distributed in the Indian Ocean, the information regarding genetic structuring and diversity has been lacking compared to its Indo Malay Archipelago counterparts. The present study was conducted to investigate the genetic stock structure of D. russelli based on mitochondrial (Cyt b) and nuclear (DrAldoB1) markers along Indian waters. The results indicated the presence of a single panmictic stock across the Indian Ocean region. High haplotype diversity associated with low nucleotide diversity suggested a population bottleneck followed by rapid population growth. Phylogenetic analysis revealed the absence of geographical clustering of lineages with the most common haplotype distributed globally. The pelagic life style, migratory capabilities, and larval dispersal may be the contributing factors to the observed spatial homogeneity of D. russelli. However, significant genetic differentiation was observed between the populations from Indian Ocean and Indo-Malay Archipelago. Hierarchical molecular variance analysis (AMOVA), pairwise FST comparisons and SAMOVA showed existence of two distinct genetic stocks of D. russelli in the Indian Ocean and IMA. The observed interpopulation genetic variation was high. A plausible explanation for the genetic differentiation observed between the Indo-Malay Archipelago and the Indian Ocean regions suggest the influence of historic isolation, ocean surface currents and biotic and abiotic features of the ocean. Also, there was a significant relationship between genetic distance and geographical distance between population pairs in a manner consistent with isolation-by-distance. These resulted in the evolution of a phylogeographic break for this species between these regions. The findings of these results suggest that D. russelli from the Indian Ocean shall be managed in its entire area of distribution as a single stock. Further, the Indian Ocean and Indo-Malayan stocks can be managed separately.

Uncovering loggerhead (Caretta caretta) navigation strategy in the open ocean through the consideration of their diving behaviour.

While scientists have been monitoring the movements and diving behaviour of sea turtles using Argos platform terminal transmitters for decades, the precise navigational mechanisms used by these animals remain an open question. Until now, active swimming motion has been derived from total motion by subtracting surface or subsurface modelled ocean currents, following the approximation of a quasi-two-dimensional surface layer migration. This study, based on tracking and diving data collected from 25 late-juvenile loggerhead turtles released from Reunion Island during their pre-reproductive migration, demonstrates the importance of considering the subsurface presence of the animals. Using a piecewise constant heading model, we investigate navigation strategy using daily time-at-depth distributions and three-dimensional currents to calculate swimming velocity. Our results are consistent with a map and compass strategy in which swimming movements follow straight courses at a stable swimming speed (approx. 0.5 m s-1), intermittently segmented by course corrections. This strategy, previously hypothesized for post-nesting green and hawksbill turtles, had never been observed in juvenile loggerheads. These results confirm a common open-ocean navigation mechanism across ages and species and highlight the importance of considering diving behaviour in most studies of sea turtle spatial ecology.

Quality Control for Ocean Current Measurement Using High-Frequency Direction-Finding Radar

High-frequency radars (HFRs) are important for remote sensing of the marine environment due to their ability to provide real-time, wide-coverage, and high-resolution measurements of the ocean surface current, wave height, and wind speed. However, due to the intricate multidimensional processing demands (e.g., time, Doppler, and space) for internal data and effective suppression of external noise, conducting quality control (QC) on radar-measured data is of great importance. In this paper, we first present a comprehensive quality evaluation model for both radial current and synthesized vector current obtained by direction-finding (DF) HFRs. In the proposed model, the quality factor (QF) is calculated for each current cell to evaluate its reliability. The QF for the radial current depends on the signal-to-noise ratio (SNR) and DF factor of the first-order Bragg peak region in the range–Doppler (RD) spectrum, and the QF for the synthesized vector current can be calculated using an error propagation model based on geometric dilution of precision (GDOP). A QC method is then proposed for processing HFR-derived surface current data via the following steps: (1) signal preprocessing is performed to minimize the effect of unwanted external signals such as radio frequency interference and ionospheric clutter; (2) radial currents with low QFs and outliers are removed; (3) the vector currents with low QFs are also removed before spatial smoothing and interpolation. The proposed QC method is validated using a one-month-long dataset collected by the Ocean State Monitoring and Analyzing Radar, model S (OSMAR-S). The improvement in the current quality is proven to be significant. Using the buoy data as ground truth, after applying QC, the correlation coefficients (CCs) of the radial current, synthesized current speed, and synthesized current direction are increased by 4.33~102.91%, 1.04~90.74%, and 1.20~62.67%, respectively, and the root mean square errors (RMSEs) are decreased by 2.51~49.65%, 7.86~27.22%, and 1.68~28.99%, respectively. The proposed QC method has now been incorporated into the operational software (RemoteSiteConsole v1.0.0.65) of OSMAR-S.

Satellite Velocity Correction Method of Ocean Current Retrieval for a Spaceborne Doppler Scatterometer

For a spaceborne pencil-beam rotating Doppler scatterometer, its precision in measuring the ocean surface motion depends on the Doppler centroid of the received signals. The Doppler centroid is determined by the relative motion between the scatterometer and the ocean surface. This relative motion includes contributions from satellite velocity, the phase velocity of resonant Bragg waves, the orbital motions of ocean waves, and the ocean surface current. Subtracting the contribution of the satellite platform velocity from the complex Doppler information is important for the application of a spaceborne Doppler scatterometer in ocean surface current retrieval. In this research, we propose a method for the platform velocity correction influenced by the Doppler centroid offset and analyze the accuracy of this correction method. The method is based on the echoed signal model of a Doppler scatterometer. Our results show that the offset could lead to a measurement offset of up to 0.02 m/s when the beam width was 0.3°. For a 0.6° beam width, the maximum offset was 0.07 m/s. Thus, with the high accuracy of the current spaceborne sensors’ measurement, the offset can be accurately eliminated. In future applications and data processing algorithms, this effect should be considered.

Detection of materially coherent eddies from satellite altimetry in the Bay of Bengal

Mesoscale eddies are a well-recognized feature of the global oceans, being of dynamical relevance to various ocean processes and of significance to transport of various species. In the last few decades, advancements in satellite observations of the sea surface have revealed mesoscale and sub-mesoscale eddy features in many parts of the ocean. An objective definition and detection of eddies has, however, remained a challenge, thus resulting in unreliable estimates of eddy formation, evolution and dissipation. In this study, we present an implementation of a Lagrangian averaged vorticity deviation (LAVD) based method to detect and characterize eddies in the Bay of Bengal (BoB), a freshwater-dominated semi-enclosed basin in the northern Indian Ocean. Systematic sensitivity studies are performed to identify parameter values that result in robust eddy detection in the BoB, and finite-time coherence in material transport associated with the LAVD-based eddies is demonstrated. LAVD-based eddy detection is then used to statistically characterize the Sri Lanka dome (SLD) eddy, an annual mesoscale cyclonic eddy of dynamical and physical importance in the southern BoB. Analysing satellite-based ocean surface currents from 27 years (1993–2019) of data, the inter-annual variability in the SLD formation, its spatio-temporal evolution and dissipation are elucidated. On an average, SLD has a lifetime of 15 weeks and a maximum area of 5 square degrees, with the longest lifetime of 38 weeks in 1996 and a maximum area of 12 square degrees in 1998. Long-lived SLDs are shown to spatially excurse into the BoB, potentially influencing large-scale transport of physical and biogeochemical properties. A potential correlation between large SLD lifetime and large variations in the monthly evolution of Dipole Mode Index and NINO3.4 is highlighted. An SSH-based Eulerian eddy detection method is also implemented to understand its efficacy in identifying materially coherent eddies in the BoB region. The paper concludes with a summary of our results, and a brief discussion of potential applications of LAVD-based eddy detection in the northern Indian Ocean.

Video Based Estimation of Surface Currents in a Tidal Inlet

Abstract Oceanic surface currents are estimated from analysis of short duration video obtained by a nadir facing camera installed on a bridge over a tidal inlet. Data analyzed consisted of 13 two-minute video clips captured approximately every 40 min over a period of 8 hr, covering a significant portion of the tidal cycle. Surface current speed and direction estimates are obtained from each collected video using (i) a method originally developed for analysis of imagery from drones (CopterCurrents) and (ii) a particle tracking method. The horizontal (u, v) surface current velocity components and total horizontal velocity magnitude, obtained from the two methods, were in very good agreement with each other (R 2 = .96 and Root Mean Square (RMS) differences of 0.12 m/s or less). Our analysis suggests that video cameras from stationary structures can provide surface flow measurements over inland waters and navigational channels where deployment of in-situ sensors is not feasible.

Characterizing the Effect of Ocean Surface Currents on Advanced Scatterometer (ASCAT) Winds Using Open Ocean Moored Buoy Data

The ocean surface current influences the roughness of the sea surface, subsequently affecting the scatterometer’s measurement of wind speed. In this study, the effect of surface currents on ASCAT-retrieved winds is investigated based on in-situ observations of both surface winds and currents from 40 open ocean moored buoys in the tropical and mid-latitude oceans. A total of 28,803 data triplets, consisting of buoy-observed wind vectors, current vectors, and ASCAT Level 2 wind vectors, were collected from the dataset spanning over 10 years. It is found that the bias between scatterometer-retrieved wind speed and buoy-observed wind speed is negatively correlated with the ocean surface current speed. The wind speed bias is approximately 0.96 times the magnitude of the downwind surface current. The root-mean-square error between the ASCAT wind speeds and buoy observations is reduced by about 15% if rectification with ocean surface currents is involved. Therefore, it is essential to incorporate surface current information into wind speed calibration, particularly in regions with strong surface currents.

Propagating Particle Tracking Uncertainty Defined by Fuzzy Numbers in Spatially Variable Velocity Fields

Accurate prediction of the trajectories of material drifting on the ocean surface is critical for risk assessment and responses to environmental emergencies. Prediction of these trajectories is subject to uncertainty arising from a number of sources, with a primary source being uncertainty in the modelled ocean surface currents and winds used as input to the trajectory model. This article presents a fuzzy number-based algorithm for propagating uncertainty through a particle tracking scheme in a time- and space-varying velocity field. The performance of the algorithm was tested by applying it to idealized, analytical velocity fields and scoring the results against the analytical solution. Both epistemic and aleatoric uncertainty were considered and combined using a fractional Brownian motion model for temporal autocorrelation of the uncertainty. In the evaluation of the algorithm, sensitivity was quantified with respect to parameters such as timestep size, resolution of the forcing velocity field, spatial and temporal gradients in the forcing, and resolution of the applied uncertainty. Parameter values optimizing uncertainty representation and computational cost were identified. The applied uncertainty was found to evolve in agreement with classical relative dispersion relationships.

Pemodelan Hidrodinamika 2-Dimensi Arus Laut Permukaan Perairan Desa Berakit Kabupaten Bintan

Information related to ocean currents is not yet available in Berakit Village waters, ocean currents are an important parameter to determine the condition of a waters. An alternative that can be used to determine the condition of ocean currents is to use hydrodynamic modeling. The purpose of the study was to analyze the distribution pattern and characteristics of surface ocean currents. This research was conducted by conducting 2-dimensional hydrodynamic modeling simulating ocean currents for 1 (one) year in December 2020-November 2021 using MIKE 21 software by sampling in 6 (six) different conditions, namely at the highest tide, lowest tide, high tide. towards the ebb and flow of the full moon, the ebb towards the negligible tide, the tide towards the ebb tide and the ebb towards the negligible tide. The model results were validated by the RMSE formula with a value of 2%, the model results were very good, so that they could be used as a reference in providing an overview of the real conditions of the pattern and current distribution at the research location. The movement of ocean currents at the time of the full moon and negligible dominant currents move towards the south of the waters, while at the time of the full tide and negligible the dominant currents move towards the north of the waters. In the north season, the current velocity ranges from 0.00006 m/s-0.125 m/s with the dominant movement towards the north. East monsoon currents move predominantly north and south with speeds ranging from 0.0000003 m/s-0.129 m/s. In the south monsoon the dominant current moves to the north and south at a speed of 0.0000007 m/s-0.13 m/s. in the west season, the dominant current moves to the north and south at a speed of 0.00001 m/s-0.12 m/s. The speed of the dominant ocean currents is greater at high tide compared to low tide, this is due to differences in sea level elevation in the opposite direction of motion.

Analysis of Doppler spectrum of a spaceborne Doppler scatterometer using an echoed signal simulation model

ABSTRACT The Doppler spectrum of a microwave scatterometer signal is determined by the relative motion between the scatterometer and the ocean surface. It is also determined by the modulation from the ocean surface backscattering coefficient. The relative motion includes contributions mainly from the motion of the platform, the phase velocity of the resonant Bragg waves, the orbital motions of ocean waves, and the ocean surface current. Estimating the Doppler centroid from the complex Doppler spectrum of the received signal is an important issue for the application of a spaceborne Doppler scatterometer in ocean surface current retrieval. In this study, we use an echoed signal simulation model based on a two-dimensional rough dynamic ocean surface to estimate the Doppler spectrum of a spaceborne Doppler scatterometer. We analyze the Doppler spectrum with different observation geometry and ocean state, and the effects of modulation on the Doppler spectrum with the pulse-pair method. Our results show that the high platform velocity and the modulation of the backscattering coefficient from the ocean surface are the main influencing factors that affect the shape of the Doppler spectrum of the received signal, which affects the accuracy of estimation of the Doppler centroid. For a Ka-band pencil-beam rotating Doppler scatterometer using the pulse-pair method, the modulation can lead to a measurement error of 1.2 m·s−1.

Multi factors-PredRNN based significant wave height prediction in the Bohai, Yellow, and East China Seas

IntroductionCurrently, deep-learning-based prediction of Significant Wave Height (SWH) is mostly performed for a single location in the ocean or simply relies on a single factor (SF). Such approaches have the disadvantage of lacking spatial correlations or dynamic complexity, leading to an inevitable growth of the prediction error with time.MethodsHere, attempting a solution, we develop a Multi-Factor (MF) data-driven 2D SWH prediction model for the Bohai, Yellow, and East China Seas (BYECS). Our model is developed based on a multi-channel PredRNN algorithm that is an improved deep-learning calculation of the ConvLSTM.ResultsIn our model, the MF of historical SWH, 10 m surface winds, ocean surface currents, bathymetries, and open boundaries are used to predict 2D SWH in the next 1-72h. Our modeled SWHs show the correlation coefficients as 0.98, 0.90, and 0.87 for the next 6h, 24h, and 72h, respectively.DiscussionAccording to the ablation experiments, winds are the dominant factor in the MF model and the memory-decoupling module is the key improvement of the PredRNN compared to the ConvLSTM. Furthermore, when the historical SWH is excluded from the input, the correlation coefficients remain around 0.95 in the 1-72h prediction due to the elimination of the error accumulation. It was worse than the MF-PredRNN with the historical SWH before 10h but better than it after 10h. Overall, for the prediction of SWH in the BYECS, our MF-PredRNN-based 2D SWH prediction model significantly improves the accuracy and extends the effective prediction time length.