or collective redistirbution of any portion of this article by photocopy machine, reposting, or other means is permitted only only permitted is means reposting, portion article or other machine, by photocopy of any of this redistirbution or collective Th ADVANCES IN COMPUTATIONAL OCEANOGRAPHY articleis has been in published Oceanography AN UNSTRUCTUREDGRID, FINITEVOLUME 19, Number journal of Th 1, a quarterly , Volume COASTAL OCEAN FVCOM SYSTEM MODEL 2006 by Th e Oceanography Society. Copyright with the approval of Th approval the with BY CHANGSHENG CHEN, ROBERT C. BEARDSLEY, AND GEOFFREY COWLES The coastal ocean extends from the land-sea interface where freshwater en- gran e Oceanography is Society. All rights reserved. Permission ters the ocean through rivers and estuaries to beyond the continental shelf. or Th e [email protected] Society. Send to: all correspondence Due in part to its shallow and complex bathymetry and coastline, the coastal ocean is quite dynamic and can feature large waves and currents driven by atmospheric storms and ocean tides, and large changes in water temperature and salinity due to seasonal changes in the surface weather and river runoff. The coastal ocean is also extremely productive, supporting a rich and di- verse ecosystem and many major fi sheries. With increasing human use and exploitation of the coastal ocean, scientifi c interest in understanding and predicting coastal ocean processes has increased dramatically. The fi rst ocean circulation model designed specifi cally for coastal application—the Princ- ted to copy this article for use in teaching and research. Repu article for use and research. this copy in teaching to ted eton Ocean Model (POM) developed by Blumberg and Mellor (1987)—led immediately to new understanding of a number of important physical phe- nomena driven by tidal and wind forcing and provided the fi rst core model e Oceanography Society, PO Box 1931, Rockville, MD 20849-1931, USA. for coupled physical-biological modeling. Although POM and the develop- ment of other coastal ocean circulation models have advanced coastal ocean science signifi cantly in the last 25 years, these existing models have limita- tions that prevent their universal application in the coastal ocean. blication, systemmatic reproduction, reproduction, systemmatic blication, 78 Oceanography Vol. 19, No. 1, Mar. 2006 ...FVCOM has been successfully applied in a number of estuarine, continental shelf, and regional/open ocean studies involving realistic model domains... Oceanography Vol. 19, No. 1, Mar. 2006 79 A state-of-the-art coastal ocean cir- nents needed in scientifi c or manage- coastal regions characterized by complex culation model system requires: (1) grid ment applications; and (5) the ability coastlines and bathymetry and diverse fl exibility to resolve complex coastline to use a wide variety of input data, es- forcing. Used widely in computational and bathymetry; (2) accurate numerical pecially as more real-time atmospheric fl uid mechanics and engineering, the methods that conserve mass, momen- and coastal ocean measurements become fi nite-volume method used in this model tum, heat, and salt; (3) proper param- available for assimilation. This model combines the advantage of fi nite-ele- eterization of vertical and horizontal system should be robust, have a fl exible ment methods for geometric fl exibility mixing; (4) modular design to facilitate user interface, and be an “open” commu- and fi nite-difference methods for simple selection of the essential model compo- nity model, supported by an expanding discrete computation (Figure 1). Verifi ed base of users that continue to improve it. through comparisons with analytical so- Changsheng Chen ([email protected]) A major step towards such a system lutions and numerical simulations made is Professor, School for Marine Science and has been taken recently by a team of with POM and other popular fi nite-dif- Technology, University of Massachusetts- University of Massachusetts-Dartmouth ference models in idealized test cases Dartmouth, New Bedford, MA, USA. Robert and Woods Hole Oceanographic Institu- (Chen et al., submitted), FVCOM has C. Beardsley is Scientist Emeritus, Depart- tion researchers (Chen et al., 2003; Chen been successfully applied in a number of ment of Physical Oceanography, Woods et al., 2004) who have developed a new estuarine, continental shelf, and region- Hole Oceanographic Institution, Woods Hole, prognostic, unstructured-grid, Finite- al/open ocean studies involving realistic MA, USA. Geoff rey Cowles is Research Volume, free-surface, three-dimensional model domains (for more information Scientist, School for Marine Science and primitive equation Coastal Ocean circu- see http://codfi sh.smast.umassd.edu). Technology, University of Massachusetts- lation Model (FVCOM) for physical and For hindcast and forecast applications, Dartmouth, New Bedford, MA, USA. coupled physical/biological studies in an integrated coastal ocean model sys- Structured Grid Unstructured Grid Model Coastline Real Coastline Ocean Figure 1. An example of fi tting a structured grid (left) and an unstructured grid (right) to a simple coastal embayment. Th e true coastline is shown in black, the model coastline in red. Note how the unstructured triangular grid can be adjusted so that the model coastline follows the true coastline, while the structured grid coastline is jagged—which can result in unrealistic fl ow disturbance close to the coast. 80 Oceanography Vol. 19, No. 1, Mar. 2006 tem has been built by coupling FVCOM servative nature of FVCOM plus its great ration with P. Rizzoli; Zang and Rizzoli, with the fi fth-generation National Cen- grid fl exibility and code simplicity make 2003) for data assimilation, (6) a fully ter for Atmospheric Research/Pennsylva- FVCOM ideally suited for interdisciplin- nonlinear ice model (implemented by F. nia State University (NCAR/Penn State) ary application in the coastal ocean. Dupont) for Arctic Ocean studies, (7) a three-dimensional sediment transport module (based on the U.S. Geological Survey community sediment transport With increasing human use and exploitation model) for estuarine and near-shore ap- of the coastal ocean, scientific interest in plications, and (8) a generalized biologi- understanding and predicting coastal cal module (GBM) for food-web dynam- ics study. GBM includes seven groups: ocean processes has increased dramatically. nutrients, autotrophy, heterotrophy, de- tritus, dissolved organic matter, bacteria, and other. With various pre-built func- tions and parameters for these groups, mesoscale meteorological model (MM5) The present version of FVCOM in- GBM allows users to either select a pre- for realistic surface forcing and the addi- cludes a number of options and compo- built biological model (e.g., NPZ, which tion of advanced data assimilation. nents (Figure 2), including: (1) choice has nutrient, phytoplankton, and zoo- of Cartesian or spherical coordinate plankton components) or to build their STRUCTURE AND FUNCTION system, (2) a mass-conservative wet/dry own biological model using the pre-de- OF FVCOM point treatment to simulate the fl ooding/ fi ned pool of biological variables and In common with other coastal ocean drying process, (3) the General Ocean parameterization functions. As shown models, FVCOM uses the modifi ed Mel- Turbulent Model (GOTM) modules in Figure 2, some components (e.g., an lor and Yamada level 2.5 (MY-2.5) and Smagorinsky turbulent closure schemes as the default for vertical and horizontal mixing and a terrain-following vertical The unstructured-grid, finite-volume methods coordinate to follow bottom topography. Unlike fi nite-difference and fi nite-ele- used in FVCOM make it an exciting new research ment models, FVCOM solves the fl ux tool for physical and interdisciplinary ocean form of the governing equations in unstructured triangular volumes with modeling studies involving domains with second-order accurate discrete fl ux complex coastlines and/or bathymetry. schemes. This numerical approach pro- vides an accurate representation of mass, momentum, heat, and salt conservation. Accurate representation is an essential (Burchard et al., 1999; Burchard, 2002) unstructured-grid surface wave model) feature of fi nite-volume methods, mak- for optional vertical turbulent mixing still need to be added to form a complete ing them widely used in other branches schemes, (4) a water-quality module to integrated coastal ocean model system, of computational fl uid dynamics where simulate dissolved oxygen and other en- which we hope to do in the near future. nonlinear advection with sharp property vironmental indicators, (5) four-dimen- FVCOM is written in Fortran 90 with gradients makes conservation of scalars sional nudging and Reduced/Ensemble MPI (Message Passing Interface) paral- (like mass and heat) diffi cult. This con- Kalman Filters (implemented in collabo- lelization, and runs effi ciently on single Oceanography Vol. 19, No. 1, Mar. 2006 81 and multi-processor computers. ferent parts of the domain as desired, when determining model grid resolution The FVCOM grid is created using a and to easily change the resolution of an for accurate simulations. Thus, FVCOM grid-generation program and two input existing grid either locally or globally. shows great utility in examining ques- fi les—the coastline fi le and bathymetry Our verifi cation studies using idealized tions of numerical convergence and de- data. While there are a number of such problems and model studies using real- termining the