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HYCOM is designed as a generalized (hybrid isopycnal/σ/z) coordinate ocean model. It is isopycnal in the open stratified ocean, but reverts to a terrain-following coordinate in shallow coastal regions, and to z-level coordinates near the surface in the mixed layer. This generalized vertical coordinate approach is dynamic in space and time via the layered continuity equation, which allows a dynamical transition between the coordinate types. Like MICOM, HYCOM allows isopycnals intersecting sloping topography by allowing zero thickness layers. HYCOM was developed from MICOM using the theoretical foundation for implementing a hybrid coordinate system set forth in Bleck and Boudra (1981; J. Phys. Oceanogr.), Bleck and Benjamin (1993; Mon. Wea. Rev.), Bleck (2002; Ocean Modelling), Chassignet et al. (2003, J. Phys. Oceanogr.) and Halliwell (2003; Ocean Modelling).
HYCOM is maintained as a single scalable/portable source code. The Gulf of Mexico model has 1/25° equatorial resolution and latitudinal resolution of 1/25° cos(lat) or ~3.5 km for each variable at mid-latitudes. It has 20 coordinate surfaces in the vertical.
This new experiment is using the latest NCODA 3dvar code instead of MVOI. As of August 2 it also uses FGAT (first guess at appropriate time) for the SST assimilation. The latest version of HYCOM is also used (2.2.36). This experiment started in March 2009 (data is available from April-2009 on) and has hourly 3d outputs available.
The data assimilation is performed using the Navy Coupled Ocean Data Assimilation (NCODA) (Cummings, 2005; QJRMS) system with a model forecast as the first guess. NCODA assimilates available satellite altimeter observations (along track obtained via the NAVOCEANO Altimeter Data Fusion Center), satellite and in situ sea surface temperature (SST) as well as available in situ vertical temperature and salinity profiles from XBTs, ARGO floats and moored buoys. The HYCOM Consortium is also in the process of evaluating other assimilation techniques, the reduced order information filter (ROIF, Chin et al., 1999; J. Geophys. Res.), the ensemble Kalman filter (Evensen, 1994; J. Geophys. Res.) and the singular evolutive extended Kalman filter SEEK filter (Pham et al., 1998; J. Mar. Syst.).
Operational Details
The system is run in real time at the Naval Oceanographic Office (NAVOCEANO) Major Shared Resource Center (the 1/25° GOM run does not use operational computer time). Ideally a 4 day hindcast and a 7 day forecast are generated and the data are made available typically within two days after the model run via servers located at the Center For Ocean-Atmospheric Prediction Studies (COAPS), Florida State University (FSU). The HYCOM format archive files are converted to CF 1.0 compliant NetCDF files using standard HYCOM post-processing package. These files contain diagnostic output at standard Levitus depth levels for several variables including: currents, temperature and salinity. The archive files are snapshots.
Detailed Information
- Run Configuration (blkdat.input)
- Contains model run configuration information such as time steps, advection scheme, mixing, vertical structure, etc.
- Model Bathymetry (depth.[ab])
- Files containing the model bathymetry.
- Computational Grids (regional.grid.[ab])
- Files containing the location of model grid point.
References
- NRL Website
- Contains snapshots, animations forecast verification statistics and model data comparisons.
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