The Models
At the core of the Northeast Coastal Ocean Forecast System (NECOFS) is the Finite-Volume Coastal Ocean Model (FVCOM) with specific regional configuration for the Gulf of Maine/Georges Bank /New England Shelf (FVCOM-GoM). The FVCOM-GoM is well suited for simulating the circulation and ecosystem dynamics from global to estuarine scales, particularly for regions characterized by irregular complex coastlines, islands, inlets, creeks, and inter-tidal zones. The FVCOM-GoM, now on its third generation (GoM3) features an unstructured grid or irregular pattern (see figures).
(figure credits: C. Chen)
The FVCOM-GoM3 model is driven at the open boundary by tidal data; at the surface by wind stress, heat flux, and net precipitation minus evaporation; at the Scotian shelf boundary by local runoff along the coast, and upstream flow. In order to improve the open boundary condition, the FVCOM-GoM3 model is being nested with a global coastal ocean model (Global-FVCOM) (see figure). The Global-FVCOM is not within the scope of this project, but is being run in concert with GoM3 to improve the open boundary condition.
In order to better resolve the complex coastline and bathymetry in Massachusetts coastal waters, the NEFCOS has been expanded with the addition of a high-resolution subdomain MASS Coastal FVCOM. This subdomain model is driven by nesting it within the regional GoM/GB domain (FVCOM-GoM3) used in NECOFS. Placed into operation in April 2009, the MASS Coastal FVCOM provides high-resolution fields of water currents, temperature, and salinity in Massachusetts coastal waters.
A final model (FVCOM SWAVE) was recently added to NEFCOS to simulate surface waves with the GoM3 and Mass Coastal FVCOM domains. This model is an unstructured-grid version of the community surface wave model SWAN.
Resolution
FVCOM-GoM3: GoM/GB FVCOM covers the entire Gulf of Maine/Georges Bank region and is enclosed by an open boundary running from the New Jersey shelf to the Scotian shelf. Horizontal resolution ranges from 0.3-1.0 km in the coastal region and over Georges Bank. A total of 40 layers are specified in the vertical. In the region deeper than 80 m, 10 uniform-thickness layers are specified in the surface and bottom boundary layers, with a transition to uniform-thickness sigma coordinate at the 90-m isobath.
MASS Coastal-FVCOM: The MASS Coastal FVCOM domain covers Massachusetts and Cape Cod Bays, the waters surrounding Cape Cod, Nantucket and Martha’s Vineyard and Buzzard Bay (referred to here as “Mass coastal waters”), with a horizontal resolution varying from 10 m in estuaries to 1 km over the outer shelf. This grid includes many smaller coastal features that are omitted in the basic GoM/GB FVCOM-GOM3 grid for this area.
Global-FVCOM: Horizontal resolution is at 20 m to 15 km; Vertical layers are at 31 or 41 or 71 s-coordinate levels.
Model Validations
An advisory council with scientists from WHOI, USGS, and NERACOOS are working with the researchers to validate model outputs, define variables and parameters for output, and develop data products for use in CMSP. The advisory council is currently deliberating ways to validate the GOM3 and Mass Coastal FVCOM models using observational data.
Variables of Interest
Below is the preliminary list of variables and parameters of interest for data output that have been identified.
|
Variable |
Parameter |
Rationale |
|
Temperature (surface and bottom) |
Mean and standard deviation |
Define seasonal cycle and variability in temperature. |
|
Salinity (surface and bottom) |
Mean and standard deviation |
Define seasonal cycle and variability in salinity. |
|
Stratification |
Mean and standard deviation of |
Define seasonal cycle and variability in stratification. |
|
Currents (surface and bottom) |
Vector-averaged mean current |
Identify persistent residual flows |
|
Currents (surface and bottom) |
Standard deviation |
Identify areas of current fluctuations (primarily tidal currents) |
|
Currents (surface and bottom) |
Standard deviation of low-pass-filtered data |
Identify areas of current fluctuations, primarily caused by wind and density variations |
|
Sea-surface height |
Standard deviation |
Identify areas of large surface fluctuations (primarily tides) |
|
Sea-surface height |
Standard deviation of low-pass-filtered data |
Identify areas of low-frequency currents |
|
Wind stress |
Vector-averaged mean and standard deviation |
Define seasonal cycle and variability in wind stress. |
|
Waves |
Significant wave height |
Define seasonal cycle and variability in waves |
|
Bottom stress (Computed from bottom currents and waves) |
Percentage of time greater than selected values (perhaps 0.1, 0.2, 0.3 N/m2) |
Define seasonal cycle of stress and identify areas of sediment resuspension |