The US Navy coupled ocean-wave prediction system

2009

The version 4 series of the Navy Coastal Ocean Model (NCOM) has been developed at the Naval Research Laboratory (NRL) and transitioned to the Navy Oceanographic Office. New capabilities include a general vertical coordinate (GVC) option in addition to the sigma-z coordinate ...

Ocean Modelling, 2006

A 1/80 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 a coordinates for the upper layers and z-levels below a user-specified depth. This flexibility allows implementation of a hybrid a-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 a-z coordinate is used to allow terrain-following a 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 a-z and pure z coordinates. Comparisons with independent temperature observations indicate that global NCOM using the a-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 7

Geoscientific Model Development Discussions

This paper describes the implementation of a coupling between a three-dimensional ocean general circulation model (NEMO) and a wave model (WW3) to represent the interactions of the upper oceanic flow dynamics with surface waves. The focus is on the impact of such coupling on upper-ocean properties (temperature and currents) and mixed-layer depths (MLD) at global eddying scales. A generic coupling interface has been developed and the NEMO governing equations and boundary conditions have been adapted to include wave-induced terms following the approach of McWilliams et al. (2004) and Ardhuin et al. (2008). In particular, the contributions of Stokes-Coriolis, Vortex and surface pressure forces have been implemented on top of the necessary modifications of the tracer/continuity equation and turbulent closure scheme (a 1-equation TKE closure here). To assess the new developments, we perform a set of sensitivity experiments with a global oceanic configuration at 1/4 o resolution coupled with a wave model configured at 1/2 o resolution. Numerical simulations show a global increase of wind-stress due to the interaction with waves (via the Charnock coefficient) particularly at high latitudes, resulting in increased surface currents. The modifications brought to the TKE closure scheme and the inclusion of a parameterization for Langmuir turbulence lead to a significant increase of the mixing thus helping to deepen the MLD. This deepening is mainly located in the Southern Hemisphere and results in reduced sea-surface currents and temperatures. 1 Introduction An accurate representation of ocean surface waves has long been recognized as essential for a wide range of applications ranging from marine meteorology to ocean and coastal engineering. Waves also play an important role in the short-term forecasting of extratropical and tropical cyclones by regulating sea-surface roughness (

2008

Prescribed by ANSI Std. Z39.18

Journal of Geophysical Research, 2007

Abstract[1] The Navy Coastal Ocean Model (NCOM) is a free-surface, primitive-equation model that is under development at the Naval Research Laboratory (NRL). The NCOM-based model of the Monterey Bay area is evaluated during a series of upwelling and relaxation wind events in August–September of 2000. The model receives open boundary conditions from a regional NCOM implementation of the California Current System and surface fluxes from the Navy Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPSTM)(COAMPS is a registered trademark of the Naval Research Laboratory). Issues investigated in this study are: NCOM-based model simulations of upwelling and relaxation events, coupling to COAMPS, use of sigma versus hybrid (sigma-z) vertical grids, and coupling with a larger-scale model on the open boundaries. The NCOM simulations were able to reproduce the observed sequence of the upwelling and relaxation events, which can be attributed, in part, to the good agreement between the observed and COAMPS winds. Comparisons with the mooring observations show that COAMPS overestimates shortwave radiation values, which makes the NCOM modeled SSTs too warm in comparison with observations. The NCOM runs forced with different resolution atmospheric forcing (3 versus 9 km) do not show significant differences in the predicted SSTs and mixed-layer depths at the mooring locations. At the same time, during the extended upwelling event, the model runs forced with 3 and 9 km resolution COAMPS fields show differences in the surface circulation patterns, which are the most distinct in the southern portion of the model domain. The model run with 9-km forcing develops a northward flow along the coast, which is not present in the run with 3-km forcing and in observations (for example, HF radar-derived radials). Comparison of the wind patterns of the 3- and 9-km products shows a weakening of the 9-km wind stress along the southern coast of the NCOM model domain, which is responsible for the development of the artificial northward flow in the NCOM run with 9-km forcing.

Journal of Physical Oceanography, 1998

Introduction: Development of an advanced global ocean prediction system has been a long-term Navy interest. Such a system must provide the capability to depict (nowcast) and predict (forecast) the oceanic "weather," some components of which include the 3D temperature, salinity, and current structure, the surface mixed layer, and the location of mesoscale features such as eddies, meandering currents, and fronts. The space scale of these eddies and meandering currents are typically ~100 km and current speeds can easily exceed 1 ms -1 in the Gulf Stream (Atlantic) and Kuroshio (Pacific). Numerical ocean models with sufficiently high horizontal and vertical resolution are needed to depict the 3D structure with accuracy superior to climatology and/or persistence (i.e., a forecast of no change). The existing two-model operational system, run daily at the Naval Oceanographic Office (NAV-OCEANO), is based on the 1/32° Navy Layered Ocean Model (NLOM) and the 1/8° Navy Coastal Ocean...

Oceanography, 2006

Prescribed by ANSI Std. Z39.18

Geoscientific Model Development

This paper describes the implementation of a coupling between a three-dimensional ocean general circulation model (NEMO) and a wave model (WW3) to represent the interactions of upper-oceanic flow dynamics with surface waves. The focus is on the impact of such coupling on upperocean properties (temperature and currents) and mixed layer depth (MLD) at global eddying scales. A generic coupling interface has been developed, and the NEMO governing equations and boundary conditions have been adapted to include wave-induced terms following the approach of McWilliams et al. (2004) and Ardhuin et al. (2008). In particular, the contributions of Stokes-Coriolis, vortex, and surface pressure forces have been implemented on top of the necessary modifications of the tracer-continuity equation and turbulent closure scheme (a one-equation turbulent kinetic energy-TKE-closure here). To assess the new developments, we perform a set of sensitivity experiments with a global oceanic configuration at 1/4 • resolution coupled with a wave model configured at 1/2 • resolution. Numerical simulations show a global increase in wind stress due to the interaction with waves (via the Charnock coefficient), particularly at high latitudes, resulting in increased surface currents. The modifications brought to the TKE closure scheme and the inclusion of a parameterization for Langmuir turbulence lead to a significant increase in the mixing, thus helping to deepen the MLD. This deepening is mainly located in the Southern Hemisphere and results in reduced sea surface currents and temperatures.