FVCOM Research Articles

Model Development and Hindcast Simulations of NOAA’s Integrated Northern Gulf of Mexico Operational Forecast System

NOAA’s National Ocean Service is upgrading three existing northern Gulf of Mexico (GOM) operational nowcast/forecast systems (OFS) by integrating them into one single system (INGOFS) and developing additional domain coverage to encompass the lower Mississippi River, Lake Pontchartrain, Texas coastal embayments, and Mexican coastal waters. The system will produce real-time nowcast and short-range forecast guidance for water levels, 3-dimensional currents, water temperature, and salinity. INGOFS will be implemented using the Finite Volume Community Ocean Model (FVCOM). This paper describes the model configuration and results from a one-year (2 August 2016–1 August 2017) hindcast simulation. The model grid is composed of about 300,000 nodes and 600,000 elements, and has a spatial resolution ranging from 45 m near the coast to around 10 km on the open ocean boundary. It uses the FVCOM wetting and drying feature, the quadratic bottom friction scheme, and the two-equation model of the Mellor-Yamada Level 2.5 turbulence closure scheme. The hindcast results of water levels, surface temperatures, and salinity were verified by comparing the model time series with in situ observations. The root-mean-squared errors are about 0.08 m for water levels, about 1.1 °C for temperatures, and about 3.7 psu for salinity. The hindcast configuration will be further tested in a nowcast/forecast environment for a one-year period. The upgraded system is anticipated to be in operational production in mid-2020.

Design and development of a service-oriented wrapper system for sharing and reusing distributed geoanalysis models on the web

Geoanalysis models are an abstraction and expression of geographic phenomena and processes which are associated to environmental issues. Such models continue to be created in many different domains, and collaborative modeling and simulation using models in the open web environment is becoming popular for geographic and environmental research. Service-oriented sharing and reusing of distributed geoanalysis models is an important foundation of this type of work. However, service-oriented modeling faces several challenges, especially associated with reusing heterogeneous geo-simulation model resources. This paper builds on research related to creating, managing, and publishing plug-and-play model services, with the aim to design and develop a web-based wrapper system for geoanalysis models that acts as a service loader and manager to publish these models as services to users. Our wrapper system can accomplish functions such as standardizing model preparation workflows, managing model services, and invoking interactive model services, thus bridging the gap between geo-simulation resource contributors and service users. We use the Soil and Water Assessment Tool (SWAT) model and the Unstructured Grid Finite Volume Community Ocean Model (FVCOM) as case studies to show that the developed wrapper system can readily and efficiently enable sharing of model resources and can contribute to collaborative modeling and simulation for environment across a network.

Flow Regimes and Adjustment to Wind‐Driven Motions in Lake Pontchartrain Estuary: A Modeling Experiment Using FVCOM

AbstractLake Pontchartrain is a brackish estuary and restricted lagoon in the microtidal northern Gulf of Mexico. Using a validated Finite Volume Community Ocean Model (FVCOM), we study the flow regimes and wind‐driven adjustment of circulation in this system. It is found that tidal currents are only significant in the eastern end near the open boundary. Local wind inside the estuary is important in driving the circulation including coastal currents. Numerical experiments confirm that the subtidal wind‐driven flow is in a quasi‐steady balance between wind stress and surface slope. Our results show that the adjustment of surface level inside the system to a sudden change in wind is a transient seiche, which dissipates within two to three cycles, each lasting ~3 hr. After the oscillations, the system reaches a new equilibrium. We show in theory that this is a damped oscillation and as wind changes, an adjustment to a new equilibrium goes much faster than a complete tidal period. This leads to the quasi steady state balance of subtidal wind‐driven flows with essentially no phase lag with wind even though wind changes with time continuously. Wind‐induced circulation behaves differently from the Csanady model with Earth rotation but similar to the prismatic lake model of Engelund without Coriolis: The coastal and shallow regions tend to have flows in the direction of wind, while the interior and deeper waters have return flows against the wind especially in bottom layer. The surface flow may not be in the direction of wind, while the bottom usually has broad and uniform counter wind flows.

Evaluating and improving modeled turbulent heat fluxes across the North American Great Lakes

Abstract. Turbulent fluxes of latent and sensible heat are important physical processes that influence the energy and water budgets of the North American Great Lakes. These fluxes can be measured in situ using eddy covariance techniques and are regularly included as a component of lake–atmosphere models. To help ensure accurate projections of lake temperature, circulation, and regional meteorology, we validated the output of five algorithms used in three popular models to calculate surface heat fluxes: the Finite Volume Community Ocean Model (FVCOM, with three different options for heat flux algorithm), the Weather Research and Forecasting (WRF) model, and the Large Lake Thermodynamic Model. These models are used in research and operational environments and concentrate on different aspects of the Great Lakes' physical system. We isolated only the code for the heat flux algorithms from each model and drove them using meteorological data from four over-lake stations within the Great Lakes Evaporation Network (GLEN), where eddy covariance measurements were also made, enabling co-located comparison. All algorithms reasonably reproduced the seasonal cycle of the turbulent heat fluxes, but all of the algorithms except for the Coupled Ocean–Atmosphere Response Experiment (COARE) algorithm showed notable overestimation of the fluxes in fall and winter. Overall, COARE had the best agreement with eddy covariance measurements. The four algorithms other than COARE were altered by updating the parameterization of roughness length scales for air temperature and humidity to match those used in COARE, yielding improved agreement between modeled and observed sensible and latent heat fluxes.

A Modeling Study on the Oil Spill of M/V Marathassa in Vancouver Harbour

The M/V Marathassa oil spill occurred on 8 April 2015 in the English Bay. In the present study, the trajectory and the transport mechanism of the spilled oil have been studied by using the three-dimensional and particle-based Oil Spill Contingency and Response (OSCAR) model forced by the Finite-Volume Community Ocean Model (FVCOM). FVCOM provided the hydrodynamic variables used by the oil spill model of OSCAR. The results showed that the fraction of the oil on the water surface and on the shoreline, as well as the amount of oil recovered were affected by the time of the initial release, the overall duration of the discharge, wind and recovery actions. The hindcast study of the M/V Marathassa oil spill showed that the likely starting time for the discharge was between 14:00 and 15:00, on 8 April 2015. The release may have lasted for a relatively long time (assumed to be 22 h in this study). The results of modeling in this study were found reasonably acceptable allowing for further application in risk assessment studies in the English Bay and Vancouver Harbour. The trajectory of the spill was mainly controlled by the tidal currents, which were strongly sensitive to the local coastline and topography of First Narrows and that in the central harbour. The model results also suggested that a high-resolution model, which was able to resolve abrupt changes in the coastlines and topography, was necessary to simulate the oil spill in the harbour.

Simulation of the 2003 Foss Barge - Point Wells Oil Spill: A Comparison between BLOSOM and GNOME Oil Spill Models

The Department of Energy’s (DOE’s) National Energy Technology Laboratory’s (NETL’s) Blowout and Spill Occurrence Model (BLOSOM), and the National Oceanic and Atmospheric Administration’s (NOAA’s) General NOAA Operational Modeling Environment (GNOME) are compared. Increasingly complex simulations are used to assess similarities and differences between the two models’ components. The simulations presented here are forced by ocean currents from a Finite Volume Community Ocean Model (FVCOM) implementation that has excellent skill in representing tidal motion, and with observed wind data that compensates for a coarse vertical ocean model resolution. The comprehensive comparison between GNOME and BLOSOM presented here, should aid modelers in interpreting their results. Beyond many similarities, aspects where both models are distinct are highlighted. Some suggestions for improvement are included, e.g., the inclusion of temporal interpolation of the forcing fields (BLOSOM) or the inclusion of a deflection angle option when parameterizing wind-driven processes (GNOME). Overall, GNOME and BLOSOM perform similarly, and are found to be complementary oil spill models. This paper also sheds light on what drove the historical Point Wells spill, and serves the additional purpose of being a learning resource for those interested in oil spill modeling. The increasingly complex approach used for the comparison is also used, in parallel, to illustrate the approach an oil spill modeler would typically follow when trying to hindcast or forecast an oil spill, including detailed technical information on basic aspects, like choosing a computational time step. We discuss our successful hindcast of the 2003 Point Wells oil spill that, to our knowledge, had remained unexplained. The oil spill models’ solutions are compared to the historical Point Wells’ oil trajectory, in time and space, as determined from overflight information. Our hindcast broadly replicates the correct locations at the correct times, using accurate tide and wind forcing. While the choice of wind coefficient we use is unconventional, a simplified analytic model supported by observations, suggests that it is justified under this study’s circumstances. We highlight some of the key oceanographic findings as they may relate to other oil spills, and to the regional oceanography of the Salish Sea, including recommendations for future studies.

Storm-driven particulate organic matter flux connects a tidal tributary floodplain wetland, mainstem river, and estuary.

The transport of terrestrial plant matter into coastal waters is important to regional and global biogeochemical cycles, and methods for assessing and predicting fluxes in such dynamic environments are needed. We investigated the hypothesis that upon reconnection of a floodplain wetland to its mainstem river, organic matter produced in the wetland would reach other parts of the ecosystem. If so, we can infer that the organic matter would ultimately become a source for the food web in the mainstem river and estuary. To accomplish this, we adapted numerical hydrodynamic and transport modeling methods to estimate the mass of particulate organic matter (POM) derived from the annually senescent aboveground parts of herbaceous marsh plants (H-POM). The Finite-Volume Community Ocean Model (FVCOM), parameterized with flow, tide, and aboveground biomass data, simulated H-POM mobilization from fluid shear stress during tidal exchange, flooding, and variable river flow; entrainment into the water column; transport via channel and overland flow; and entrapment when wetted surfaces dry. We examined export from a recently reconnected, restoring tidal emergent marsh on the Grays River, a tributary to the Columbia River estuary. Modeling indicated that hydrologically reconnecting 65ha at the site resulted in export of about 96×103 kg of H-POM, primarily during pulsed storm flooding events in autumn and early winter. This exported mass amounted to about 19% of the summer peak aboveground biomass measured at the site. Of that 19%, about 48% (47×103 kg) was deposited downstream in the Grays River and floodplain wetlands, and the remaining 52% (50×103 kg) passed the confluence of the Grays River and the mainstem estuary located about 7km from the study site. The colonization of the restoring study site largely by nonnative Phalaris arundinacea (reed canarygrass) may have resulted in 18-28% lower H-POM mobilization than typical marsh plant communities on this floodplain, based on estimates from regional studies of marshes dominated by less recalcitrant species. We concluded that restored floodplain wetlands can contribute significant amounts of organic matter to the estuarine ecosystem and thereby contribute to the restoration of historical trophic structure.

Development of a wave-current model through coupling of FVCOM and SWAN

A coupled wave-current system has been developed in the present paper based on two open source community models, the Finite-Volume Community Ocean Model (FVCOM) and the Simulating WAves Nearshore (SWAN) using Model Coupling Toolkit (MCT). The coupled system runs on unstructured grids and multiple processors, and information, including water elevations and currents from FVCOM and wave parameters from SWAN, exchanges between FVCOM and SWAN in both on-line and two-way manners. The system was evaluated against laboratory experiments and the evaluation showed that the simulated results agree well with the measured data. Compared to the existing off-line coupling system based on FVCOM and SWAN, the system in the present study is able to accomplish the on-line, two-way coupling, and at the same time, is more efficient for computations and easier to use for the nearshore wave-current simulations.

Temporal and spatial characteristics of potential energy anomaly in Lake Taihu.

In this study, water temperature and meteorological data in Lake Taihu from June 11 to July 6, 2013, are collected to calibrate and verify the unstructured grid finite-volume community ocean model (FVCOM) coupled with a heat exchange module. The spatial and temporal variations of potential energy anomalies (PEA) in the lake, simulated by the calibrated FVCOM, are analyzed to explore the stratification and de-stratification processes in water body. The temporal variation of PEA primarily follows the diurnal cycles of solar radiation, while the spatial heterogeneity of PEA is jointly determined by solar radiation and vertical shear of horizontal velocity coupled with the topography of the lake. The maxima of PEA in the lake are not greater than 4J/m3 in the summer and even smaller along shore regions and near the Pingtaishan station. This study is helpful to improve understanding of the effect of physical processes on the algae bloom in Lake Taihu.

Improving the Persian Gulf sea surface temperature simulation by assimilating the satellite data via the ensemble Kalman

One of the indicators representing the permissible performance of a marine model is the capability of model in providing an accurate spatiotemporal distribution of the thermal structure of domain. Data assimilation is taken into account as an expedient platform in order to achieve this goal. In this paper, the ensemble Kalman filter (EnKF) was applied as a data assimilation scheme to enhance the sea surface temperature (SST) simulation and whereupon the underwater temperature of the Persian Gulf in the finite volume community ocean model (FVCOM). The daily satellite measured SST data that obtained from advanced very high-resolution radiometer pathfinder were considered as observational assimilation data. The comparisons between the results of both proposed models including FVCOM and SST measurements were carried out to evaluate the efficiency of data assimilation. The comparisons revealed a meaningful improvement in the assimilated simulation of the spatiotemporal SST variability in the whole domain, especially in the shallow parts and near the Hormuz Strait. The root-mean-square error reduced significantly in assimilation run. The statistical comparisons of the results bias denote a positive impact of the data assimilation.

Simulation of Wave‐Current Interactions Under Hurricane Conditions Using an Unstructured‐Grid Model: Impacts on Ocean Waves

AbstractThe effect of wave‐current interactions on ocean waves under hurricane conditions is investigated through application of the unstructured‐grid finite‐volume community ocean model (FVCOM) coupled to the unstructured‐grid surface wave model (SWAVE) in the North Atlantic Ocean. We study wave‐current interactions during the life cycles of extratropical hurricanes Juan (2003) and Bill (2009) as they propagate from subtropical waters to midlatitudes in the Northwest Atlantic. Simulations of wave parameters in each hurricane are shown to compare well with buoy and satellite altimeter observations, in terms of winds, significant wave heights, wave energy spectra, and wave directions. This is partially achieved by restricting the drag coefficient. It is well known that the maximum intensity of tropical cyclones depends on the ratio of the enthalpy coefficient to the drag coefficient. The latter increases with wind speed, levels off with category one hurricanes and may drop for even higher winds. In our study, we find that setting a limiting value on the drag coefficient improves the simulations of waves at peak storm intensities. Simulation of wave‐current interactions is also shown to improve the simulation of the wave heights and wave energy spectra. This is notable at the peak of the storms, in comparisons with observations from buoys in areas of both deep water and relatively shallow water. The effect of currents on significant wave heights is shown to reach 0.4 m for hurricane Juan and 1.0 m for hurricane Bill, or as much as about ±10% for wave heights distributed along the storm track.

Using Satellite Altimetry to Calibrate the Simulation of Typhoon Seth Storm Surge off Southeast China

Satellite altimeters can capture storm surges generated by typhoons and tropical storms, if the satellite flies over at the right time. In this study, we show TOPEX/Poseidon altimeter-observed storm surge features off Southeast China on 10 October 1994 during Typhoon Seth. We then use a three-dimensional, barotropic, finite-volume community ocean model (FVCOM) to simulate storm surges. An innovative aspect is that satellite data are used to calibrate the storm surge model to improve model performance, by adjusting model wind forcing fields (the National Center for Environment Prediction (NCEP) reanalysis product) in reference to the typhoon best-track data. The calibration reduces the along-track root-mean-square (RMS) difference between model and altimetric data from 0.15 to 0.10 m. It also reduces the RMS temporal difference from 0.21 to 0.18 m between the model results and independent tide-gauge data at Xiamen. In particular, the calibrated model produces a peak storm surge of 1.01 m at 6:00 10 October 1994 at Xiamen, agreeing with tide-gauge data; while the peak storm surge with the NCEP forcing is 0.71 m only. We further show that the interaction between storm surges and astronomical tides contributes to the peak storm surge by 34% and that the storm surge propagates southwestward as a coastally-trapped Kelvin wave.

FVCOM one-way and two-way nesting using ESMF: Development and validation

Built on the Earth System Modeling Framework (ESMF), the one-way and two-way nesting methods were implemented into the unstructured-grid Finite-Volume Community Ocean Model (FVCOM). These methods help utilize the unstructured-grid multi-domain nesting of FVCOM with an aim at resolving the multi-scale physical and ecosystem processes. A detail of procedures on implementing FVCOM into ESMF was described. The experiments were made to validate and evaluate the performance of the nested-grid FVCOM system. The first was made for a wave-current interaction case with a two-domain nesting with an emphasis on qualifying a critical need of nesting to resolve a high-resolution feature near the coast and harbor with little loss in computational efficiency. The second was conducted for the pseudo river plume cases to examine the differences in the model-simulated salinity between one-way and two-way nesting approaches and evaluate the performance of mass conservative two-way nesting method. The third was carried out for the river plume case in the realistic geometric domain in Mass Bay, supporting the importance for having the two-way nesting for coastal-estuarine integrated modeling. The nesting method described in this paper has been used in the Northeast Coastal Ocean Forecast System (NECOFS)-a global-regional-coastal nesting FVCOM system that has been placed into the end-to-end forecast and hindcast operations since 2007.

3D underwater sound propagation in coastal environments

Underwater sound propagation in a coastal ocean can be influenced by a variety of physical oceanographic conditions that are unique in the coastal and estuarine environment, such as salt wedge fronts, river-plume induced nonlinear internal gravity waves, strong tidal currents, surf zone waves, etc. The confined boundaries in the area can also produce reflection, diffraction and even scattering of sound due to shoaling seafloor. The morphological dynamics in the area is complex and results in corrugated and channeled bathymetry, which may cause 3D ducting and trapping of sound. In this talk, we will present our numerical study of 3D underwater sound propagation in Long Island Sound, a tidal estuary of the Atlantic Ocean. The Unstructured Grid Finite Volume Community Ocean Model (FVCOM) will be utilized to simulate physical oceanographic processes and produce water-column environmental input to the sound propagation model. A bathymetric database from high-resolution multibeam surveys will also be used to in...

Environmental drivers of epibenthic megafauna on a deep temperate continental shelf: A multiscale approach

Evaluating the role of abiotic factors in influencing the distribution of deep-water (>75–100 m depth) epibenthic megafaunal communities at mid-to-high latitudes is needed to estimate effects of environmental change, and support marine spatial planning since these factors can be effectively mapped. Given the disparity in scales at which these factors operate, incorporating multiple spatial and temporal scales is necessary. In this study, we determined the relative importance of 3 groups of environmental drivers at different scales (sediment, geomorphology, and oceanography) on epibenthic megafauna on a deep temperate continental shelf in the eastern Gulf of Maine (northwest Atlantic). Twenty benthic photographic transects (range: 611–1021 m; total length surveyed: 18,902 m; 996 images; average of 50 ± 16 images per transect) were performed in July and August 2009 to assess the abundance, composition and diversity of these communities. Surficial geology was assessed using seafloor imagery processed with a novel approach based on computer vision. A bathymetric terrain model (horizontal resolution: 100 m) was used to derive bathymetric variability in the vicinity of transects (1.5, 5 km). Oceanography at the seafloor (temperature, salinity, current speed, current direction) over 10 years (1999–2008) was determined using empirical (World Ocean Database 2013) and modelled data (Finite-Volume Community Ocean Model; 45 vertical layers; horizontal resolution: 1.7–9.5 km). The relative influence of environmental drivers differed between community traits. Abundance was enhanced primarily by swift current speeds, while higher diversity was observed in coarser and more heterogeneous substrates. In both cases, the role of geomorphological features was secondary to these drivers. Environmental variables were poor predictors of change in community composition at the scale of the eastern Gulf of Maine. This study demonstrated the need for explicitly incorporating scales into habitat modelling studies in these regions, and targeting specific drivers for community traits of interest.

Correcting the Sea Surface Temperature by Data Assimilation Over the Persian Gulf

In this paper, the impact of sea surface temperature (SST) data assimilation on the results of a finite volume community ocean model has been examined by using the nudging scheme. In this regard, the advanced very high-resolution radiometer satellite SST data were selected as the observational data for assimilation. The numerical modeling was performed over the Persian Gulf from 1998 to 2003 in two different modes: with and without SST data assimilation. The performance of data assimilation with the nudging scheme was evaluated by comparing the simulated SST with the in situ SST measurements and optimum interpolation SST data. Both the spatial and temporal comparisons show the efficiency of assimilation in correcting the model results. The spatial root mean square error in the assimilated run depicts meaningful improvements in the whole of the domain. Also, the temporal comparisons of the results show the capability of assimilation in lowering the model output errors. The simulated SST obtained by applying the data assimilation in the shallow parts of the Persian Gulf matched exactly with the measured ones, especially near the Hormuz Strait. Finally, the results show significant improvements in the SST simulated by using the nudging schemes.

Turbulent Heat Fluxes during an Extreme Lake-Effect Snow Event

Abstract Proper modeling of the turbulent heat fluxes over lakes is critical for accurate predictions of lake-effect snowfall (LES). However, model evaluation of such a process has not been possible because of the lack of direct flux measurements over lakes. The authors conducted the first-ever comparison of the turbulent latent and sensible heat fluxes between state-of-the-art numerical models and direct flux measurements over Lake Erie, focusing on a record LES event in southwest New York in November 2014. The model suite consisted of numerical models that were operationally and experimentally used to provide nowcasts and forecasts of weather and lake conditions. The models captured the rise of the observed turbulent heat fluxes, while the peak values varied significantly. This variation resulted in an increased spread of simulated lake temperature and cumulative evaporation as the representation of the model uncertainty. The water budget analysis of the atmospheric model results showed that the majority of the moisture during this event came from lake evaporation rather than a larger synoptic system. The unstructured-grid Finite-Volume Community Ocean Model (FVCOM) simulations, especially those using the Coupled Ocean–Atmosphere Response Experiment (COARE)-Met Flux algorithm, presented better agreement with the observed fluxes likely due to the model’s capability in representing the detailed spatial patterns of the turbulent heat fluxes and the COARE algorithm’s more realistic treatment of the surface boundary layer than those in the other models.

An empirical formula for maximum wave setup based on a coupled wave-current model

The present paper proposes an empirical formula for maximum wave setup based on a coupled wave-current model. The wave model is the Simulating Waves Nearshore (SWAN) model; the current model is the Finite Volume Community Ocean Model (FVCOM). This study first evaluates the coupled model system against mean water level data collected from a series of laboratory and field experiments. The model calculation agrees with the measurements. Then, the study uses the model results from simulations with a range of wave conditions to develop an empirical formula for the maximum wave setup as a function of wave height, wavelength in deep water, and beach slope. The formula agrees with experimental and in situ measurements and shows better performance than previous formulas.

A discrete global grid system for earth system modeling

ABSTRACTTo support Earth system modeling, we propose a discrete global grid system that expresses multi-resolution spatial data. Specifically, a unified coding model that expresses a grid of nodes, edges, and cells is constructed for a triangular discrete global grid system. To fulfill the requirements of practical applications, we design a code-based topological query method for this grid system and an algorithm to transform between grid codes and geographic coordinates. We evaluate the Global Finite Volume Community Ocean Model (Global-FVCOM) on the triangular discrete global grid system in the proposed uniform coding model. The ocean tidal waves simulated by the Global-FVCOM running on the coded grid are then compared with results obtained using a traditional irregular spherical grid system, and the results display comparable accuracy. The uniform coding model proposed in this paper provides a triangular discrete global grid system that can represent multi-resolution spatial data and can be used in Earth system models. This unified coding model can also be applied to the geographic coordinate system made up of latitudes and longitudes, as well as diamond and hexagonal grids.

Wind-Driven Dissolved Organic Matter Dynamics in a Chesapeake Bay Tidal Marsh-Estuary System

Controls on organic matter cycling across the tidal wetland-estuary interface have proved elusive, but high-resolution observations coupled with process-based modeling can be a powerful methodology to address shortcomings in either methodology alone. In this study, detailed observations and three-dimensional hydrodynamic modeling are used to examine biogeochemical exchanges in the marsh-estuary system of the Rhode River, MD, USA. Analysis of observations near the marsh in 2015 reveals a strong relationship between marsh creek salinity and dissolved organic matter fluorescence (fDOM), with wind velocity indirectly driving large amplitude variation of both salinity and fDOM at certain times of the year. Three-dimensional model results from the Finite Volume Community Ocean Model implemented for the wetland system with a new marsh grass drag module are consistent with observations, simulating sub-tidal variability of marsh creek salinity. The model results exhibit an interaction between wind-driven variation in surface elevation and flow velocity at the marsh creek, with northerly winds driving increased freshwater signal and discharge out of the modeled wetland during precipitation events. Wind setup of a water surface elevation gradient axially along the estuary drives the modeled local sub-tidal flow and thus salinity variability. On sub-tidal time scales (>36 h, <1 week), wind is important in mediating dissolved organic matter releases from the Kirkpatrick Marsh into the Rhode River.