Formulation, implementation and examination of vertical coordinate choices in the Global Navy Coastal Ocean Model (NCOM)

A 1/8� global version of the Navy Coastal Ocean Model (NCOM) is described with details of its formulation, implementation, and configuration of the vertical coordinate. NCOM is a baroclinic, hydrostatic, Boussinesq, free-surface ocean model that allows its vertical coordinate to consist of r coordinates for the upper layers and z-levels below a user-specified depth. This flexibility allows implementation of a hybrid r–z coordinate system that is expected to mitigate some of the weaknesses that can be associated with either pure coordinate option. For the global NCOM application, the r–z coordinate is used to allow terrain-following r coordinates in the upper ocean, providing better resolution and topographic fidelity in shelf regions where flow is most sensitive to its representation. Including z coordinates for deeper regions efficiently maintains high near-surface vertical resolution in the open ocean. Investigation into the impact of the selected coordinate system focuses on differences between atmospherically-forced free-running (no assimilation) global solutions using r–z and pure z coordinates. Comparisons with independent temperature observations indicate that global NCOM using the r–z coordinate has improved skill relative to its z coordinate implementation. Among other metrics, we show that in comparison with time series of surface temperature from National Oceanic Data Center (NODC) buoys, mostly located in coastal regions, root mean squared differences (RMSD) improved for 63% and correlation improved for 71% of the stations

[1]  Ross J. Murray,et al.  Explicit Generation of Orthogonal Grids for Ocean Models , 1996 .

[2]  H. Hurlburt,et al.  Climatological SST and MLD Predictions from a Global Layered Ocean Model with an Embedded Mixed Layer , 2003 .

[3]  Paul J. Martin,et al.  Navy Real-time Global Modeling Systems , 2002 .

[4]  Rainer Bleck,et al.  Salinity-driven Thermocline Transients in a Wind- and Thermohaline-forced Isopycnic Coordinate Model of the North Atlantic , 1992 .

[5]  M. Banner,et al.  Modeling Wave-Enhanced Turbulence in the Ocean Surface Layer , 1994 .

[6]  W. R. Holland,et al.  Application of a Third-Order Upwind Scheme in the NCAR Ocean Model* , 1998 .

[7]  S. Levitus,et al.  An Approximation to the Equation of State for Sea Water, Suitable for Numerical Ocean Models , 1972 .

[8]  Caskey,et al.  GENERAL CIRCULATION EXPERIMENTS WITH THE PRIMITIVE EQUATIONS I . THE BASIC EXPERIMENT , 1962 .

[9]  Peter A. Rochford,et al.  The Impact of Water Turbidity on Interannual Sea Surface Temperature Simulations in a Layered Global Ocean Model , 2004 .

[10]  A. Blumberg,et al.  Diagnostic and prognostic numerical circulation studies of the South Atlantic Bight , 1983 .

[11]  Eric P. Chassignet,et al.  North Atlantic Simulations with the Hybrid Coordinate Ocean Model (HYCOM): Impact of the Vertical Coordinate Choice, Reference Pressure, and Thermobaricity , 2003 .

[12]  A. Blumberg,et al.  Circulation Modelling using Orthogonal Curvilinear Coordinates , 1987 .

[13]  Frank J. Millero,et al.  International one-atmosphere equation of state of seawater , 1981 .

[14]  Paul J. Martin,et al.  Description of the Navy Coastal Ocean Model Version 1.0 , 2000 .

[15]  N. Heaps,et al.  Three-dimensional coastal ocean models , 1987 .

[16]  Hernan G. Arango,et al.  Developments in terrain-following ocean models: intercomparisons of numerical aspects , 2002 .

[17]  Antonio J. Busalacchi,et al.  A Pilot Research Moored Array in the Tropical Atlantic (PIRATA) , 1998 .

[18]  Alan J. Wallcraft,et al.  Sea Surface Temperature Sensitivity to Water Turbidity from Simulations of the Turbid Black Sea Using HYCOM , 2005 .

[19]  Paul J. Martin,et al.  Validation of interannual simulations from the 1/8° global Navy Coastal Ocean Model (NCOM) , 2006 .

[20]  J. Nihoul,et al.  Three-dimensional models of marine and estuarine dynamics , 1987 .

[21]  H. Hurlburt,et al.  A Numerical Study of Loop Current Intrusions and Eddy Shedding , 1980 .

[22]  G. Mellor,et al.  Development of a turbulence closure model for geophysical fluid problems , 1982 .

[23]  S. Zalesak.  Fully multidimensional flux-corrected transport algorithms for fluids , 1979 .

[24]  J. Smagorinsky,et al.  GENERAL CIRCULATION EXPERIMENTS WITH THE PRIMITIVE EQUATIONS , 1963 .

[25]  W. Large,et al.  Oceanic vertical mixing: a review and a model with a nonlocal boundary layer parameterization , 1994 .

[26]  Frank J. Millero,et al.  A new high pressure equation of state for seawater , 1980 .

[27]  H. Hurlburt,et al.  Sea Surface Height Predictions from the Global Navy Coastal Ocean Model During 1998-2001 , 2004 .

[28]  G. Mellor.  An Equation of State for Numerical Models of Oceans and Estuaries , 1991 .

[29]  J. Beckers,et al.  On the use of the σ-coordinate system in regions of large bathymetric variations , 1992 .

[30]  Melinda S. Peng,et al.  Navy Operational Global Atmospheric Prediction System (NOGAPS): Forcing for Ocean Models , 2002 .

[31]  Rainer Bleck,et al.  An oceanic general circulation model framed in hybrid isopycnic-Cartesian coordinates , 2002 .

[32]  G. Mellor,et al.  A Hierarchy of Turbulence Closure Models for Planetary Boundary Layers. , 1974 .

[33]  John D. McCalpin.  A comparison of second‐order and fourth‐order pressure gradient algorithms in a σ‐co‐ordinate ocean model , 1994 .

[34]  Alan F. Blumberg,et al.  Modeling vertical and horizontal diffusivities with the sigma coordinate system , 1985 .

[35]  G. Halliwell,et al.  Evaluation of vertical coordinate and vertical mixing algorithms in the HYbrid-Coordinate Ocean Model (HYCOM) , 2004 .

[36]  H. Hurlburt,et al.  Air–Sea Flux Estimates And The 1997–1998 Enso Event , 2002 .

[37]  Antonio J. Busalacchi,et al.  The Tropical Ocean‐Global Atmosphere observing system: A decade of progress , 1998 .

[38]  P. Martin.  Simulation of the mixed layer at OWS November and Papa with several models , 1985 .

[39]  A. H. Murphy,et al.  Skill Scores Based on the Mean Square Error and Their Relationships to the Correlation Coefficient , 1988 .

[40]  Richard Asselin,et al.  Frequency Filter for Time Integrations , 1972 .