Three-dimensional Princeton Ocean Model Research Articles

3D Numerical Simulation of Kuroshio-induced Wake Near Green Island, Taiwan

In this research, Kuroshio-induced vortex shedding in the lee of Green Island was numerically studied using the three-dimensional Princeton Ocean Model. The temporal and spatial characteristics of the vortex street were analyzed at different tidal levels, wind fields and water depths. The nu-merical results were validated by comparing with in-situ measurements from the Green Island tidal station, shipboard acoustic doppler current profiler (ADCP), conductivi-ty-temperature-depth (CTD) profiler, and moderate resolution imaging spectroradiometer (MODIS) satellite image datasets. Also, the three-dimensional results of velocity, temperature, and salinity fields were compared well with observational data. Furthermore, the influence depths of the wind effect and vor-tex shedding were found to be approximately 100 and 300 meters, respectively. The aspect ratio and dimensionless width were evaluated to be 3.64 and 1.46, respectively. In addition, the temporal scales (Strouhal number), and propagation speeds were analyzed at various water depths. Finally, the elongation of the Kuroshio-induced vortex street was studied under wind and tide effects at various water depths.

Three-Dimensional Simulations of Wind Effects on Green Island Wake

The aim of the present study is to apply the three-dimensional Princeton Ocean Model to study the wind effects on Kuroshio-induced island wake in the lee of Green Island, Taiwan. Numerical results indicate that the effect of NE winds squeezes the Kuroshio-induced island vortex street close to the coast and the SW winds tend to push the island vortex street farther away from the coast. The simulated vortex streets are analyzed by the dimensionless spatial lengths to quantify the prescribed feature. By comparing the three-dimensional results with different wind conditions, the Ekman transports are observed and the influence depths of wind effects are studied. Additionally, some cold eddies are found in temperature fields resulting from numerical simulations. These results are in qualitative agreement with field measurements and satellite images.

Comparison between the response of the Northwest Pacific Ocean and the South China Sea to Typhoon Megi (2010)

The upper-ocean responses to Typhoon Megi (2010) are investigated using data from ARGO floats and the satellite TMI. The experiments are conducted using a three-dimensional Princeton Ocean Model (POM) to assess the storm, which affected the Northwest Pacific Ocean (NWP) and the South China Sea (SCS). Results show that the upwelling and entrainment experiment together account for 93% of the SST anomalies, where typhoon-induced upwelling may cause strong ocean cooling. In addition, the anomalous SST cooling is stronger in the SCS than in the NWP. The most striking feature of the ocean response is the presence of a two-layer inertial wave in the SCS—a feature that is absent in the NWP. The near-inertial oscillations can be generated as typhoon wakes, which have maximum flow velocity in the surface mixed layer and may last for a few days, after the typhoon’s passage. Along the typhoon tracks, the horizontal currents in the upper ocean show a series of alternating negative and positive anomalies emanating from the typhoon.

Impact of Sea-State-Dependent Langmuir Turbulence on the Ocean Response to a Tropical Cyclone

Abstract Tropical cyclones are fueled by the air–sea heat flux, which is reduced when the ocean surface cools due to mixed layer deepening and upwelling. Wave-driven Langmuir turbulence can significantly modify these processes. This study investigates the impact of sea-state-dependent Langmuir turbulence on the three-dimensional ocean response to a tropical cyclone in coupled wave–ocean simulations. The Stokes drift is computed from the simulated wave spectrum using the WAVEWATCH III wave model and passed to the three-dimensional Princeton Ocean Model. The Langmuir turbulence impact is included in the vertical mixing of the ocean model by adding the Stokes drift to the shear of the vertical mean current and by including Langmuir turbulence enhancements to the K-profile parameterization (KPP) scheme. Results are assessed by comparing simulations with explicit (sea-state dependent) and implicit (independent of sea state) Langmuir turbulence parameterizations, as well as with turbulence driven by shear alone. The results demonstrate that the sea-state-dependent Langmuir turbulence parameterization significantly modifies the three-dimensional ocean response to a tropical cyclone. This is due to the reduction of upwelling and horizontal advection where the near-surface currents are reduced by Langmuir turbulence. The implicit scheme not only misses the impact of sea-state dependence on the surface cooling, but it also misrepresents the impact of the Langmuir turbulence on the Eulerian advection. This suggests that explicitly resolving the sea-state-dependent Langmuir turbulence will lead to increased accuracy in predicting the ocean response in coupled tropical cyclone–ocean models.

Response of southwest monsoon winds on shelf circulation off Kerala Coast, India

Three-dimensional Princeton Ocean Model is used to investigate the dynamics of the shelf flow response to the spatial and temporal variability of the wind stress forcing along the Kerala Coast. The model is configured for the west coast of India with higher horizontal resolution near the coast. In the vertical, a terrain following sigma coordinate is used, having finer resolution near the surface and bottom. In the present study, an attempt is made to understand the variability of the surface circulation and associated SST during July–August for 2000 and 2002 as a response of daily wind stress forcing derived from the QSCAT winds. The southerly current during July–August supports upwelling processes along the Kerala Coast. From the available buoy observations and simulations, it is noted that the coastal current reverses its direction to either off-shore or northward if the wind magnitude reduces suddenly below 3ms−1 towards the coast. In this event, the coastal upwelling is inhibited by the reversal of currents and it results an increase in the local SST. The reversal of currents is explained in terms of local vorticity generated as a result of reduction of wind magnitude near the coast.

Impact of stratification on internal waves and differential wearing of thermal inversions on the east coast of India

The surface layers of the Bay of Bengal along the east coast of India exhibit intricate stratification owing to the differential distribution of freshwaters. The winter (January–February) cooling of the salinity-induced stable layers results in the development of thermal inversions that deteriorate toward the end of the season. The study focuses on the behavior of the thermal inversions in the light of the variable stratification and the monsoon imposed reversing coastal current. To address the associated processes, a three-dimensional Princeton Ocean Model is applied for the east coast of India, and numerical experiments carried out to study the means by which the thermal inversions tend to perish with the passage of winter. The model domain with variable curvilinear grid uses input fields that comprise realistic bathymetry and initial temperature/salinity conforming to winter/specified stratification. The surface forcing comprises wind stress and diurnal pattern air–sea heat fluxes. The body forcing is derived from the periodic tidal elevations at the open boundaries. It has been found that the thermal inversions tend to sustain as the equator-ward flowing East India Coastal Current (EICC) traps the cool low saline waters between Paradip and Kakinada. The current off Paradip is weak and variable and is not a part of EICC. Consequently, in the absence of replenishment of cool and freshsurface waters, the temperature/salinity gradients get eroded steadily. No thermal inversions are noticed south of Kakinada because of relatively weak current with diminished vertical salinity gradient. As the nature of stratification encountered in the bay is highly variable due to diverse reasons, the behavior of internal waves under different stratification scenarios is also addressed. Numerical experiments indicate that the energy/amplitude of the internal waves are comparable in the surface layers for any stratification, where as it is certain orders exalted in the deeper waters of the strong stratification scenario. Further, it is found that the energies and pattern of the temperature oscillations conform to the nature of mixed tide at the corresponding latitude. The underneath stratification is found to be more responsible for the generation of internal waves compared to the local stratification. This implies that the body forcing emanating from below is the cardinal contributor for the generation of internal waves. The numerical experiment with a flat and uniform bottom showing weak manifestation of internal waves endorses the same. This connotes that the continental slopes are an effective generator of the internal waves and the energy flux conversion of the barotropic tide to internal waves seems to be heavily dependent on the shoaling bottom.

Mixing in the surface layers in association with internal waves during winter in the northwestern Bay of Bengal

The upper ocean has complex and variable temperature stratification, and the surface layers in the northwest Bay of Bengal in winter indicate the presence of transient thermal inversions that wane with the advancement of the season. During winter, the sea surface loses heat and the surface waters of the coastal regions of the east coast of India are fairly stratified with the residual freshwater atop from the preceding southwest monsoonal discharge. The vertical stability favors the formation and sustenance of temperature inversions. To investigate the mechanism and the influence of ubiquitous internal waves that thrive on stability, a three-dimensional Princeton Ocean Model is configured for the east coast of India and is applied to study the process in the surface layers in association with the internal waves. The model domain constitutes a variable curvilinear grid, and the input fields comprise bathymetry, initial temperature and salinity, wind stress, air-sea heat fluxes and tidal forcing at the open boundaries. The numerical experiments demonstrate that vertical stability alone cannot cause, support or augment the internal wave oscillations, if the stratification is attributed to salinity only. Internal waves may therefore be perceived in stable layers, essentially from temperature-induced stratification. Despite stratification and enough vertical density gradient in the upper ocean, the conditions may not suit for the occurrence of internal waves due to thermal diffusive processes that overpower the salinity gradients. The vertical spreading of heat due to double diffusion is believed to be transparent to tidal forcing as the generation of internal waves is subdued even under density stratification. The model simulations indicate that the horizontal convergence/divergence motions, required for the manifestation of internal waves at the surface are inhibited in the presence of temperature inversion. The available SAR imageries in winter endorse the model simulations to this effect.

Investigation of the generation and propagation of low frequency internal waves: A case study for the east coast of India

SAR (Synthetic Aperture Radar) images in the northwest Bay of Bengal indicate the existence of internal waves and their occurrence and intensity is topography dependent as indicated by in-situ data and satellite information. To complement and comprehend the observations, a three-dimensional Princeton Ocean Model is applied to study the generation and propagation of internal waves. The model domain is configured with a variable curvilinear grid and the input fields comprise bathymetry, initial temperature and salinity, wind stress, air-sea heat flux and tidal information. The numerical investigation indicated a predominant activity of internal waves in the north, and the rationale is three-fold. The first one could be the stable stratification due to fresh water discharge from head-bay major river system, secondly, the significant magnitude/range of the tides and finally, the bathymetry in the coastal waters off Paradip is about 12% shallower compared to that of Visakhapatnam and further south. The cumulative effect of these causes the predominance of internal waves in the north. The core of the energy is essentially in the low-frequency range and the model is able to simulate semi-diurnal and diurnal components reasonably well up to 6 h frequency (0.162 cph).

Role of Fresh Water Discharge from Rivers on Oceanic Features in the Northwestern Bay of Bengal

The circulation of northwestern Bay of Bengal is modeled using a three-dimensional Princeton Ocean Model (POM). Orthogonal curvilinear grid is used to get a higher resolution along the coastal boundaries. Numerical simulations on climatological scale for premonsoon were compared with those with and without fresh water during monsoon season. The simulations for monsoon season without freshwater discharge at head Bay show intensification of the premonsoon features. The presence of lower SSTs and higher sea surface salinities as compared to premonsoon season along the coast substantiate this observation. The pole-ward moving East Indian Coastal Current (EICC) extends along-shore up to 20.5°N. Simulations with freshwater discharge for Monsoon season indicate that freshwater plume constitutes an equator-ward moving EICC branch opposing the pole-ward moving branch. The freshwater discharge modifies sea surface elevations along the northwestern coastal Bay of Bengal, in turn suppressing the coastal upwelling. Absence of freshwater plume imparts a significant change in the oceanic features in north western parts of Bay of Bengal.

Effect of River Discharge on Bay of Bengal Circulation

The seasonal circulation and mixed layer depths in Bay of Bengal is modeled using the three-dimensional Princeton Ocean Model (POM). Along the coastal boundaries a higher resolution is accomplished using the curvilinear orthogonal grid. Model uses a free-surface and terrain following sigma coordinates. The initial climatological salinity and temperature fields for the model are derived from the World Ocean Atlas-2001(WOA01). The Model is forced with wind stress derived from COADS wind climatology. Bilinear interpolation is used to obtain the initial fields and wind stress to the required model specification. Using the seasonal fields and wind stress the model is integrated for simulating Bay of Bengal circulation. The numerical simulations on climatological scale for monsoon months were conducted to study the evolution of dynamics. The simulations bring out not only the typical characteristic features of fresh water plume along the coast but also intensification of the flow over the monsoon period. The increase in the fresh water flow found to affect only the western parts of the BoB. The opposing currents due to monsoon winds and southward flowing fresh water discharge (FWD) were also delineated. The model results show that the wind stress induced turbulence process is subdued in the presence of strong vertical salinity stratification due to the influence of FWD. The simulated mixed layer depths are in agreement with the reported analytical energy required for mixing values.

Pre-monsoon Variability of Ocean Processes along the East Coast of India

Abstract A three-dimensional Princeton Ocean Model has been configured for the east coast of India to study the circulation and coastal upwelling during the pre-monsoon season of 2000. The model uses an orthogonal curvilinear grid and a terrain-following sigma coordinate in the vertical with monthly data fields of temperature and salinity from “Levitus94.” The model is applied to study the coastal ocean processes and its variability on weekly timescales off the east coast of India. The forcing in the model is the real-time weekly averaged wind stress obtained from Quik Scattero-meter/National Center for Environmental Prediction blended wind of May 2000. The discernable variability in the winds of May 2000 over the weekly timescale influenced the surface layers reflected in the 3-day mean satellite images. To simulate this feature and to understand the dynamics, numerical experiments are carried out with the associated real-time winds. Both diagnostic and prognostic computations are used for this, and the ...

홍수기 낙동강 하천플륨의 3차원 거동해석

Behavior of the Nakdong River plume was studied by the analysis of the observed CTD data and numerical simulations using three-dimensional Princeton Ocean model (POM) in which the river discharge, tides and winds were considered. During the flood season of summer the 30 psu isohaline expands northward to Daebyeon and southwestward to Samcheonpo. The model results show that the isohalines are approximately parallel to the bottom slope, which suggests the possibility of upwelling induced by the topographic effects. Northwesterly wind expands the river plume to the offshore direction so that the inflow of fresh plume water into Jinhae Bay through the Gaduk Channel is constrained, then the coastal upwelling seems to be caused by the wind-driven current at the southern edge of Gaduk Island. Southwesterly wind expands the river plume toward Daebyeon, and the inflow of fresh water into Jinhae Bay is also constrained.

A three-dimensional model study of the Mediterranean outflow

Evaporation over the Mediterranean basin produces a salty water mass that overflows the relatively narrow and shallow Strait of Gibraltar. The outflow is investigated with the three-dimensional Princeton Ocean Model. The model makes use of a bottom-following, sigma-coordinate system and an imbedded turbulence closure scheme to simulate the bottom boundary layer. Starting as a channel flow confined by the sidewalls of the trench of the westernmost part of the Strait, the bottom boundary current descends the steep continental slope of the eastern Gulf of Cadiz. The flow is controlled by a balance of the pressure gradient and the Coriolis acceleration, entrainment and bottom friction. Downslope Ekman fluxes are largest at the shelf break near the entrance of the Strait where we observe the most pronounced entrainment of North Atlantic Central Water. Profiles of modeled horizontal velocity, as well as scalar and turbulent quantities, show a remarkable resemblance to observed features. The model reproduces the “nose” shape of the velocity profile that is typical for a density current; below the velocity maximum, there is a well-mixed layer and a stratified shear layer exists above the nose. The evolution of water mass properties along the path of the outflow agrees favorably with observations and the sensitivity of the Mediterranean outflow (MO) to varying source water properties is investigated. The combined effect of initial stratification, differential entrainment, and routing by the topography leads to the evolution of the well-known two-core structure of the bottom layer. Whereas the upper part of the outflow continues to follow the continental slope northward in the form of a bottom boundary current after it passes Cape St. Vincent, the lower core separates from the slope and there is a lateral spreading of the saline and warm outflow water in the depth range of the lower salinity maximum (centered at about 1200 m). The outflow becomes hydrodynamically unstable and lenses of saline water shed from the core, carrying their water mass characteristic into the Atlantic. The model results confirm that the area of Cape St. Vincent is a prominent formation area for Mediterranean water (MW) eddies (Meddies).

Computer Simulations of Wind-induced Estuarine Circulation Patterns and Estuary-shelf Exchange Processes: The Potential Role of Wind Forcing on Larval Transport

Wind and density (salinity) driven circulation patterns in the Croatan-Albemarle-Pamlico Estuarine System (CAPES), North Carolina and its interaction with shelf waters via inlets were investigated using the three-dimensional Princeton Ocean Model (POM). This study examines the sensitivity of three-dimensional flow within the CAPES and the exchange of water mass between the CAPES and continental shelf to eight different wind directions. The results indicate that stochastic wind forcing could interact with the topography of coastline and the geographic locations of inlet sources of larvae, to produce spatiotemporal variation in larval supply to potential estuarine nursery habitats. Larval transport between Pamlico, Croatan and Albemarle Sounds, and exchange between estuary and shelf can have horizontal and vertical variations. Thus, three dimensional models coupled with information on larval vertical migration behavior, are required to explain inshore migration and settlement patterns of estuarine-dependent finfish and crustaceans.

A Numerical Investigation of the Gulf Stream and Its Meanders in Response to Cold Air Outbreaks

The three-dimensional Princeton Ocean Model is used to examine the modification of the Gulf Stream and its meanders by cold air outbreaks. Two types of Gulf Stream meanders are found in the model. Meanders on the shoreward side of the Gulf Stream are baroclinically unstable. They are affected little by the atmospheric forcing because their energy source is stored at the permanent thermocline, well below the influence of the surface forcing. Meanders on the seaward side of the stream are both barotropically and baroclinically unstable. The energy feeding these meanders is stored at the surface front separating the Gulf Stream and the Sargasso Sea, which is greatly reduced in case of cold air outbreaks. Thus, meanders there reduce strength and also seem to slow their downstream propagation due to the southward Ekman flow. Heat budget calculations suggest two almost separable processes. The oceanic heat released to the atmosphere during these severe cooling episodes comes almost exclusively from the upper water column. Transport of heat by meanders from the Gulf Stream to the shelf, though it is large, does not disrupt the principal balance. It is balanced nicely with the net heat transport in the downstream direction.