Clockwise Eddy Research Articles

Ocean Circulation and Variability in the Seram and Northern Banda Seas

Abstract The Seram and Banda Seas (SBS) convey the eastern pathway of Indonesian Throughflow (ITF) from Maluku and Halmahera inflow portals. This study aims to investigate circulation and variability at near-surface and thermocline layers in the SBS region using validated INDESO model output datasets (2008-2015). It is shown that much warmer and saltier thermocline ITF water (24,36°C and 34,65 psu) from Halmahera is predominant, flowing southward and impinging on the northern coast of Seram near 128.5°E. The flows then bifurcate eastward into the Banda outer ring arc and westward into Banda via the Manipa Strait and western Seram Seas. In Banda, two clockwise eddies are found related to these inflows. Secondary southward inflow via Lifamatola is associated with cooler and less salty water (23,3°C and 34,45 psu), which merges with ITF Halmahera. The variability of oceanographic parameters is dominated by the annual period. However, on an interannual scale, the response of seawater temperature to ENSO is evident, and its amplitude, as shown by the principal component time series EOF, is much stronger in Banda than in Seram at -2.7. A decreasing trend of seawater temperature was also found in 2015.

Influence and characteristics of anticyclonic eddies in active MHW years in the Northwest Atlantic

The Northwest Atlantic contains two subregions, the Gulf of Maine and the Mid-Atlantic Bight. This region is dynamically controlled by the Jet Stream, the Gulf Stream, (GS) and its eddies. Anticyclonic eddies (AEs) (warm core clockwise eddies) and cyclonic eddies (cold core counterclockwise eddies) influence oceanic properties as they are shed by the GS and dissipated in the Northwest Atlantic. Marine Heatwaves (MHWs) are extreme temperature events that cause ecological damage in the Northwest Atlantic where drivers for these events are abundant. This work focuses on four major MHW active years (2012, 2016, 2017, and 2020) and observes the characteristics of MHWs, AEs, and oceanic parameters, such as Ocean Heat Content, Mixed Layer Depth, temperature, and salinity anomalies. Depth profiles, lead-lag covariance and correlations, and comparisons of events reveal dynamics of MHW intensification in these four years. AE radius, amplitude, and eddy kinetic energy (EKE) were less variable in the MHW years of 2012, 2016, and 2017 but have a weak relationship with MHW intensity. The Gulf of Maine had the strongest (above 0.80) correlation between GS eddy heat flux convergence and MHW intensity. The 2012 MHWs were shown to be strongly influenced by the GS in addition to atmospheric forcings, as were the 2017 Gulf of Maine MHWs. The 2020 MHWs experienced a number of forcings from the Jet Stream, the GS, and AEs, with the highest intensity events occurring at depths below 100 m. We conclude that better understanding how regional dynamics and multiple drivers intensify MHWs to form MHW active years is key to modelling and forecasting future extreme events.

Characteristics Analysis of Fluid Flow and Heating Rate of a Molten Bath Utilizing a Unified Model in a DC EAF

Herein, a 2D unified model coupling a plasma arc–molten bath–cavity in a direct current electric arc furnace was developed for a characteristic analysis of the fluid flow and heating rate of the molten bath. The ‘local thermodynamic equilibrium–diffusion approximation’ method was employed for the physical phenomenon at the plasma arc/molten bath interface, and the volume-of-fluid method was used to track the free surface. After ensuring model validation, the formation processes of the cavity and the flow field and heating rate of the molten bath were investigated by utilizing the unified model. The numerical results showed that the formation processes of the cavity contained three stages, namely the expansion, compression, and dynamic equilibrium stages. The arc pressure and plasma shear stress both contributed to the cavity formation, and dominated the expansion of the cavity depth and diameter, respectively. Under plasma arc jet impingement, there were two flow patterns inside the molten bath: (i) a clockwise eddy on the top surface and lateral part of molten bath dominated by plasma shear stress, and (ii) a counter-clockwise eddy in the bottom part of the molten bath dominated by the electromagnetic force. Meanwhile, the main heated region of the molten bath with the plasma arc–molten bath–cavity coupling was in the radial range of 0.2–0.6 m, and a high-temperature region was formed on the top surface of the molten bath caused by plasma shear stress.

Numerical Analysis of Fluid Flow and Heat Transfer by Means of a Unified Model in a Direct Current Electric Arc Furnace

Herein, a unified 2D axially symmetric model coupling the plasma arc and molten bath in a direct current electric arc furnace is established, with the physical phenomena at the plasma arc/molten bath interface to be confronted by the “local thermodynamic equilibrium diffusion approximation” method. After ensuring model validation and grid independence test, the fluid flow and heat transfer processes are analyzed. The numerical investigation reveals that in terms of the relative importance of driving forces in the molten bath, an anticlockwise eddy is formed at the molten bath center driven by electromagnetic force, whereas a clockwise eddy is formed near the lateral part of the molten bath driven by buoyancy force. Regarding the distribution of heat flux, the convection–conduction and radiation heat govern the rate of heat transfer from the plasma arc to the molten bath. In addition, for larger arc current, higher arc power in the plasma arc region and higher heating rates in the molten bath are obtained when the arc length is held constant; for shorter arc length, lower arc power in the plasma arc region but higher heat transfer efficiency in the molten bath is attained when the arc current is held constant.

Interdecadal variability of the Western Subarctic Gyre in the North Pacific Ocean

Interdecadal variations of the Western Subarctic Gyre (WSAG) in the North Pacific were examined mainly by analysis of absolute dynamic topography (ADT) during 1993–2017. The ADT was based on altimetry-derived sea level anomalies superimposed on state-of-the-art mean dynamic topography. We specified geostrophic surface streamlines of the WSAG associated with closed isolines of the ADT. The WSAG intensity was the strongest in the late 1990s, when the WSAG was zonally contracted, and it decreased to the mid-2010s in a linear manner with time. The WSAG expanded abruptly toward the east around 2001 in a step function–like manner. After this abrupt shift, the WSAG was connected most strongly to the Alaskan Gyre. This condition persisted even into the late 2010s. The shift to the very elongated pattern was also accompanied by a drastic lowering of the ADT around 170°W, 50°N, where the WSAG and Alaskan Gyre had been distinctly separated by a peak of the ADT during the previous period when the shape of the gyre was less elongated. A reduced-gravity model of wind-induced, long, baroclinic Rossby waves with weak dissipation could account for both the interdecadal weakening of the WSAG and the step function–like lowering of the ADT peak at the time of the shift of the WSAG to the very elongated pattern. In addition to the baroclinic response of the subarctic ocean to basin-scale wind stress, mesoscale clockwise eddies contributed to sea level rise around the center of the WSAG. In particular, there was an interdecadal increase in the frequency of appearance of strong, mesoscale, clockwise eddies that were generated south of the Aleutian Islands at longitudes of 170°E−180°. Those eddies propagated approximately to the west-southwest, and they disappeared around the center of the WSAG.

Horizontal Structure of Banda Eddies and The Relationship to Chlorophyll-a During South East Monsoon in Normal and ENSO Period on 2008-2010

Banda Sea is part of Indonesia Fisheries Management Area (WPP 714) which famous for Tuna fisheries. In addition to being influenced by Indonesian Through Flow (ITF), the Banda Sea also influenced by eddies. Banda eddies and the relationship to chlorophyll-a were studied by using the output of ocean circulation model produced by INDESO (Infrastructure Development of Space Oceanography) project in Ministry of Marine Affair and Fisheries. Data from 2008 to 2011 during normal phase of South East Monsoon period (June-August 2008), El Nino phase (June-August 2009), and La Nina phase (June-August 2010) were used. The model results showed two clockwise eddies in the northern of Banda Sea and three counterclockwise eddies in the southern of Banda Sea. The clockwise eddies were found at 20 meter depth and induced upwelling in south water of Buru Island, Ambon Island and Lease Island (Haruku, Saparua and Nusalaut Islands). Otherwise, counterclockwise eddies in the southern of Banda Sea (north of Wetar Island and Yamdena Island) generate the downwelling. High vorticity value of the eddy was found in the northern of Wetar Island. The presence of Banda Eddies on South East Monsoon period play an important role to maintain the water mass balance in the Banda Sea. Eddies also have strong influence on nutrient sinking from the surface of water. In addition, the eddies vorticity increased during the La Nina period and lead to low surface chlorophyll-a in the surface of the Banda Sea.

Marine macro debris transport based on hydrodynamic model before and after reclamation in Jakarta Bay, Indonesia

Jakarta Bay as an area with the densest population in Indonesia became one of the highest contamination level waters in the world includes pollution of debris. Reclamation activities in Jakarta Bay will change the water conditions will also affect the distribution of debris at sea. Therefore, this study conducted to determine the movement of the macro debris before and after island reclamation in Jakarta Bay. The method used is a model that simulated by the hydrodynamic model and particle trajectory model. Data needed for the hydrodynamic model were wind, tides, bathymetry, and shoreline, while for the trajectory of the particles using a data type of macro debris, debris weight, and debris flux. Hydrodynamics simulations indicate if a reclamation island formation does not change surface current patterns significantly, but causes a decrease in the flow velocity of ± 0.002 to 0.02 m/s at some point. The trajectory of particles of debris indicate if after reclamation, debris tends to accumulate in the eastern Jakarta Bay in the rainy season (January) as there are anticlockwise eddy current, as well as in the western and eastern regions during the dry season (July), because there is a clockwise eddy current in the eastern Jakarta Bay.

Numerical study of keyhole behaviors and thermal fluid flow in high current plasma arc welding

A fully coupled plasma arc-keyhole-weld pool model was developed to investigate the keyhole behaviors and thermal fluid flow in high current plasma arc welding. The relationship between the forces distribution and fluid flow patterns was revealed. Owing to a constraint effect of the water cooling nozzle, the plasma arc flows downward with high energy and momentum, so a large keyhole forms. Inside the keyhole, the plasma arc mainly flows downward, and very few plasma arc flows upward along the keyhole wall. At the top surface of the keyhole, the plasma arc flows outward. The dominant downward plasma shear stress and negative arc pressure in the z direction cause a dominant anti-clockwise eddy in the weld pool. The outward plasma arc shear stress on the top weld pool surface causes a small clockwise eddy in the weld pool.

Tidal and tidal current characteristics in the Guangxi Gulf of Tonkin, South China Sea

The Guangxi Gulf of Tonkin (GXGT) is rich in mineral, oceanic energy, and biological resources; however, it has not attracted much attention. Based on ECOMSED, a high-resolution three-dimensional numerical model is constructed in this study, and the accuracy is validated using long-term observational data. The results showed that the GXGT is dominated by regular diurnal tide and mixed mainly diurnal tidal currents and some regions to the northwest and south of Weizhou Island are dominant by mixed mainly semi-diurnal tidal currents. Furthermore, the rotation direction of O1 is found to be counter-clockwise and clockwise in the western and eastern domains, respectively, whereas the rotation directions of the other three tidal constituents are clockwise and counter-clockwise in the open sea and coastal bays, respectively. Similarly, the propagation direction of the tidal energy flux of O1 (northwestward) is different from them of the other three tidal constituents (northeastward) in the western GXGT. On the other hand, the propagation directions of the four tidal constituents are all northeastward in the eastern GXGT. A comparison of the reference run with the summed-up effect of six runs, where each of the tidal constituents has been considered separately, revealed that the nonlinear effect due to the interaction of the six tidal constituents cannot be neglected in the GXGT, especially in the western GXGT. Interestingly, energy input from wind to O1 is larger than that to M2 whereas the tidal dissipation of O1 is less than that of M2 at BBL. Additionally, tidally induced residual currents mostly flow westward in the GXGT, with clockwise eddies present outside the Qinzhou Bay and Tieshan Port. Driven by the monsoon wind, the current structure and strength in the GXGT have obvious seasonal variation. And sensitive experiments show that the residual currents in the GXGT are deeply influenced by the monsoon wind and bottom topography.

Flow characteristics inside droplets moving in a curved microchannel with rectangular section

A micro-particle image velocimetry system is used to study the internal flow field of droplets in a curved channel, with consideration of the effects of capillary number, viscosity ratio, droplet size, channel curvature, and interfacial tension on the flow field. It is found from the experiment that there is a clockwise eddy in the upper part of the droplet, and three more in the lower part, of which the left and right ones are counterclockwise and the middle one is clockwise. By adjusting the above parameters, the flow field structure transitions can be realized. Either the decrease in the viscosity ratio, droplet size, channel curvature, and interfacial tension or the increase in capillary number will all weaken the effect of the lower gap oil film on the movement of the droplets, resulting in disappearance of the lower intermediate eddy. In case the droplet size is further reduced, the two eddies below will gradually approach and merge. After the addition of more surfactants, the eddy at the lower portion of the droplet may not form a complete rotating structure, or be transferred to other planes inside the droplet, and the eddy originally presented in the upper portion of the droplet expands to occupy the entire droplet. The results of this study are useful for screening high-throughput cell manipulation application reaction conditions, further expanding the application range of flow cytometry, and providing experimental support for extraction, synthesis, and heat and mass transfer directly relying on the internal convection of droplets.

Rip current circulation and surf zone retention on a double barred beach

Rip currents have an important control on the exchange of water and advected materials such as sediment and pollutants, between the surf zone and inner shelf. Concurrent in situ Eulerian and Lagrangian (GPS drifter) data of surf zone waves and currents were combined with video data on wave breaking patterns over the inner and outer bars on a high energy, double-barred beach. The data collectively show how the occurrence of wave breaking over the outer bar changes the behavior of a channel rip current, and the exchange process. On both days, there was a prominent clockwise eddy in the surf zone, for which the seaward-heading portion formed a rip current in a well-defined channel rip, incised into the inner bar. Exit rate (measured with drifters) from the surf zone to inner shelf decreased significantly with increased wave breaking over the outer bar, from 71% exits to 6% over the two days. Exit rate appears to be driven by the balance between wave breaking over the inner and outer bars and pulsing of currents within the surf zone. Under higher wave conditions, there were stronger pulsations in surf zone currents and more surf zone exits. However, higher wave conditions caused wave breaking over the outer bar. This breaking increases vorticity around the outside of the surf zone eddy, which increases surf zone retention. This is in contrast to previous studies showing that vorticity is highest at the center of surf zone eddies. Under such conditions, drifter exits were rare, and occurred due to vortex shedding. During lower incident wave conditions, eddy vorticity was lower, and drifters could relatively freely exit the surf zone. This is one of the few studies that investigate surf zone circulation on a high energy, double-barred beach.

Influence of magnetic field on nanofluid free convection in an open porous cavity by means of Lattice Boltzmann method

In this paper, magnetohydrodynamic nanofluid hydrothermal analysis in an open porous cavity is presented by means of Lattice Boltzmann method. Brownian motion influence on nanofluid properties is considered by means of Koo-Kleinstreuer-Li (KKL) model. Roles of Rayleigh number (Ra), Hartmann number (Ha), nanofluid volume fraction (ϕ) and Darcy number (Da) are depicted. Results indicate that the rate of exiting warmer fluid enhances with rise of Darcy and Raleigh numbers. The shape of streamline changes with increase of the Darcy number and buoyancy forces and the clockwise eddy diminish with increase of Rayleigh numbers. Temperature gradient reduces with increase of Lorentz forces.

Interdecadal decrease in potential fishing areas for Pacific saury off the southeastern coast of Hokkaido, Japan

AbstractWe examined interdecadal variations in potential fishing grounds for the Pacific saury, Cololabis saira, off the southeastern coast of Hokkaido, Japan, for the early fishing season of August–September. We applied linear trend analysis to a time series of several oceanographic variables for 1993–2014. Trends in the appearance frequency of sea surface temperatures (SST) of 12–18 °C during August–September indicated an interdecadal reduction in the potential fishing area off the Hokkaido coast. There were localized significant increases of both SST and the sea level anomaly along the Kuril–Kamchatka Trench off the Hokkaido coast. The localized trends coincided with decadal decreases of satellite‐based chlorophyll concentrations after 2002. Analysis of mesoscale eddies revealed that the localized trends were related to clockwise (counterclockwise) eddies that appeared more frequently (less frequently) near the trench in recent years. Moreover, the Oyashio transport on the slope between the coast and the trench decreased significantly and completely disappeared in some recent summers. Interactions between the Oyashio and mesoscale eddies resulted in an interdecadal shift in the cold‐water intrusion along the main stream of the Oyashio from the along‐slope direction to the offshore direction in the upstream region of the Hokkaido coast, and large areas of favorable potential fishing grounds near the Hokkaido coast have disappeared in recent years.

Sudden strong current generated by an eddy in the eastern part of Wakasa Bay, Japan

A sudden strong coastal current called a “kyucho” occurred in August 2013 in the eastern coastal waters of Wakasa Bay, Japan. This study examined its characteristics based on both observational data collected by intensive field investigations and the simulation results of a numerical model. The field investigations comprised moored buoy observations near the coast and voyages by a research vessels and fishing boats. The mooring observations indicated that a current speed exceeding 50 cm s−1 occurred abruptly near the eastern coast of the bay, in association with a synchronous change in the current direction. Data collected by acoustic Doppler current profilers (ACDPs) mounted on the vessels showed that a clockwise eddy existed in the bay and that the current on the east side of the eddy generated the kyucho near the coast. Based on the results of the numerical model and the analysis of the ADCP data, it was considered that the clockwise eddy was generated by a strong current at the tip of the Tango Peninsula, in the western part of the bay. As the eddy propagated from west to east across the bay, it induced the kyucho in the coastal waters in the east of the bay.

Surface current patterns observed by HF radar: methodology and analysis of currents to the north of the Yaeyama Islands, East China Sea

A new method was developed to compare the classifications of different kind of data maps based on the self-organizing map (SOM) analysis. The surface current maps of the northern coast of Ishigaki and Iriomote Islands, East China Sea, observed by high-frequency (HF) radar were classified by SOM. Winds, sea surface temperatures (SST), and reanalysis data were also classified by SOM. The optimum area for classification was determined objectively by the new method, which relates these patterns to HF radar current patterns. We found two typical surface patterns: the first was that northeastward flows are dominant in the observation area and the second was that a clockwise eddy was also dominant in this area. The southwestward wind pattern was strongly related to the dominant clockwise eddy pattern of the HF radar current field.

Evaluating the surface circulation in the Ebro delta (northeastern Spain) with quality-controlled high-frequency radar measurements

Abstract. The Ebro River delta is a relevant marine protected area in the western Mediterranean. In order to promote the conservation of its ecosystem and support operational decision making in this sensitive area, a three-site standard-range (13.5 MHz) CODAR SeaSonde high-frequency (HF) radar was deployed in December 2013. The main goal of this work is to explore basic features of the sea surface circulation in the Ebro deltaic region as derived from reliable HF radar surface current measurements. For this aim, a combined quality control methodology was applied: firstly, 1-year long (2014) real-time web monitoring of nonvelocity-based diagnostic parameters was conducted to infer both radar site status and HF radar system performance. The signal-to-noise ratio at the monopole exhibited a consistent monthly evolution, although some abrupt decreases (below 10 dB), occasionally detected in June for one of the radar sites, impacted negatively on the spatiotemporal coverage of total current vectors. It seemed to be sporadic episodes since radar site overall performance was found to be robust during 2014. Secondly, a validation of HF radar data with independent in situ observations from a moored current meter was attempted for May–October 2014. The accuracy assessment of radial and total vectors revealed a consistently high agreement. The directional accuracy of the HF radar was rated at better than 8°. The correlation coefficient and root mean square error (RMSE) values emerged in the ranges [0.58–0.83] and [4.02–18.31] cm s−1, respectively. The analysis of the monthly averaged current maps for 2014 showed that the HF radar properly represented basic oceanographic features previously reported, namely, the predominant southwestward flow, the coastal clockwise eddy confined south of the Ebro delta mouth, or the Ebro River impulsive-type freshwater discharge. The EOF analysis related the flow response to local wind forcing and confirmed that the surface current field evolved in space and time according to three significantly dominant modes of variability.

A case study of large phytoplankton blooms off the New Jersey coast with multi-sensor observations

Taking the 2011 summer bloom as a study case, we investigated the transport and nutrient delivery mechanisms for large phytoplankton blooms of the New Jersey coast. The horizontal advection of the chlorophyll is approximately one order larger than the horizontal diffusion averaging the whole study area. And the sea surface currents are found to correlate with the wind stress but only for part of the middle shelf. Based on the horizontal advection simulation driven by HF radar current, the bloom is divided into three sub-regions. The northern coastal section of the bloom shows high–low–high pattern in chlorophyll time series, which is related to coastal upwelling and a clockwise eddy. Coastal currents play an important role in the eddy formation and the southward transport of the bloom. The southern coastal section of the bloom is supported by the nutrients from coastal upwelling and driven offshore by wind. The northeast section of the bloom is fueled by nutrient source upwelled through Ekman pumping. The magnitude of Ekman pumping is of the same order as the magnitude of the upwelling along the coast. These identified mechanisms could also applied to more than half of bloom events during 2002 to 2013. In the summer of 2011 off the coast of New Jersey, processes in different sub-regions worked together, leading to this large phytoplankton bloom.

Interdecadal decrease of the Oyashio transport on the continental slope off the southeastern coast of Hokkaido, Japan

AbstractWe investigated the interdecadal trend of Oyashio velocity and transport during 1993–2011 based mainly on linear trend analysis of altimetry and in situ temperature‐salinity data from a monitoring line (“A‐line”) off the southeastern Hokkaido coast. Significant trends of increasing sea level were detected on the continental slope, north of the Kuril‐Kamchatka Trench. Sea level anomaly data revealed a localized clockwise circulation centered near the trench, the suggestion being that the strength of the Oyashio on the slope and the offshore return flow had decreased. The Oyashio mainstream seemed to have shifted from a nearshore to an offshore path. Steric heights estimated from the A‐line data exhibited an increasing trend north of the trench, where 50–80% of the increase was determined by halosteric components attributable to a trend of decreasing salinity in the subsurface. The trend of decreasing salinity was related to downward displacement of isohaline/isopycnal surfaces. The largest displacement was above the trench. Horizontal pressure gradients associated with southwestward flows on the slope were weakened. The Oyashio transport decreased by 8.9 Sv (106 m3 s−1) in 19 years. A mesoscale eddy analysis revealed that clockwise eddies appeared more frequently in recent years near the trench around the A‐line and could decrease the Oyashio transport. A baroclinic, long Rossby‐wave model also predicted that a large‐scale baroclinic response to the wind stress could weaken the Oyashio velocity in the upper layer. Dynamical linkage between the localized eddies and large‐scale response remains to be clarified in future work.

The turbulent structure of the flow field generated by a hydrofoil in stalling condition beneath a water–air interface

In this paper, measurements beneath the interface of the flow past a hydrofoil in water during stalling conditions are used to characterise the flow field and to extract and to analyse the small eddies using an original algorithm based on the wavelet transform. The detected eddies are analysed to evaluate their spatial distribution and their intensity separating the wake of the foil-related from the wake of the breaker-related eddies. The wake of the foil-related eddies have an almost symmetric distribution of circulation with slight dominance of counter-clockwise (CCW) eddies, while the breaker-related eddies have an asymmetric distribution of circulation, and clockwise (CW) eddies are dominant. The joint probability density function (PDF) of the turbulent kinetic energy (TKE) and the Reynolds shear stress is computed by referring to the time-averaged values in the area occupied by the eddies. A similar PDF computed using the instantaneous values during eddies presence shows values of TKE and Reynolds shear stress roughly twice the average values, i.e., eddies can be associated to larger fluctuations of the flow field respect to the time average flow field. However, on average, the Reynolds shear stress during eddy presence is less than the Reynolds shear stress of the time-averaged flow at the same location. The sign of the Reynolds shear stress is systematically opposite to the time-averaged value in quadrants Q2–Q4 for CW eddies and in quadrants Q1–Q3 for CCW eddies. Therefore, in the presence of eddies there is a counter-flux of momentum. The conditional analysis of the terms of the TKE balance indicates that, in the wake of the foil and during the presence of eddies, the production is ≈15% stronger than the time-averaged production at the same location occupied by the eddies. Beneath the free surface the production is ≈30% weaker than the time average. A similar analysis for the advection indicates that, in the wake of the foil, the advection in the presence of eddies is an order of magnitude greater (in absolute value) than the advection due to the time-averaged flow at the same location. Additionally, beneath the free surface, the advection in the presence of eddies is much greater than the average. A similar behaviour can be observed for the transport term due to turbulence. Therefore, in the presence of eddies, production plus advection plus transport is enhanced with respect to the average flow and is increased approximately by 40% in the wake of the foil and 20% beneath the free surface.

태풍통과시 3차원 원시모델을 이용한 녹산만 담수역의 시공간 변화특성

Temporal and spatial variation in the freshwater region, created by river runoff, of a small bay, caused by the passage of typhoons was examined using a three-dimensional primitive equation model (the Princeton Ocean Model, POM). Numerical experiments were implemented focusing on temporal evolution in the freshwater region in association with typhoon tracks. The model domain covered most of the estuary around the Nakdong River, including Noksan Bay, where river water is periodically released from upstream (Noksan dam). The model showed that the extension of the freshwater region outside of the bay depended strongly on the tracks of typhoons, specifically the associated wind directions and inner flow fields that are accompanied by new clockwise eddies. The model also showed that entrainment from typhoon passage frequently creates salt wedges in the estuary, indicating that organisms in the bay are biologically and chemically influenced with variation in the freshwater region.