System Description

The system is configured for the global ocean with HYCOM 2.2 as the dynamical model. Computations are carried out on the GLBb0.08 computational grid but here the output served on the uniform GLBu0.08 grid. There are 32 vertical layers (see blkdat.input). The bathymetry is derived from the 30-arc second GEBCO dataset. Surface forcing is from 1-hourly National Centers for Environmental Prediction (NCEP) Climate Forecast System Reanalysis (CFSR) with horizontal resolution of 0.3125° and includes wind stress, wind speed, heat flux (using bulk formula), and precipitation. The diurnal cycle is adequately resolved because of the temporal frequency of the input forcing. For additional details on the model configuration such as layer reference densities time steps, advection scheme, mixing etc. see blkdat.input. Except for the input forcing, the configuration of this Ocean Reanalysis is the same as the Global Ocean Forecast System 3.0, i.e. GLBa0.08-90.X and 91.X also served at hycom.org.

Note that the experiment number changes from 19.0 to 19.1 in August 1995 because the integration of the hindcast was moved from the Navy DoD Supercomputing Resource Center (DSRC) IBM Power 6 (DaVinci) to the IDataPlex (Kilrain) supercomputer. There were small changes to NCODA, but none that should have any significant impact on the model solution.

How It's Generated:

• NRL interpolates the archive file from GLBa0.08 to GLBu0.08, using isubaregion. Note that this now reads in a "gmap" file that defines the mapping between the two grids. Therefore, isubaregion only does the interpolation (isuba_gmapi, only run once, calculates the actual bi-linear remapping weights).
• Next, NRL runs archv2ncdf3z on the resulting file using the new "NAVOCEANO" (netCDF) output type (interpolated to 40 standard z-levels). Only five fields provided: SSH, eastward velocity, northward velocity, temperature, and salinity. Note: NRL writes out in-situ temperature, not potential temperature.

Topography

• NRL interpolates this data to a uniform 0.08 degree lat/lon grid between 80.48S and 80.48N. GLBa0.08 uses the native Mercator-curvilinear HYCOM grid whereas GLBu0.08 is the constant .08 deg lat/lon grid onto which the netcdf files have been interpolated (in the horizontal and vertical). This type of grid is easy to use with GIS tools, and it starts at -180.0E because this works best in ARCOAS.

NAVOCEANO's netCDF Format

• This format uses short ints to store the fields (which saves space).

Data Assimilation

The system uses the Navy Coupled Ocean Data Assimilation (NCODA) system (Cummings, 2005, Cummings and Smedstad, 2013) for data assimilation. NCODA uses the model forecast as a first guess in a 3D variational scheme and assimilates available satellite altimeter observations (along track obtained via the Naval Oceanographic Office (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. MODAS synthetics are used for downward projection of surface information (Fox et al., 2002).

• Incremental updating over 6 hours, from the NCODA analysis at 12Z the previous day until 18Z
• Because this was run in hindcast mode and all available data were available, it simply integrated forward one day at a time
• NCODA analysis and assimilation over basin-wide areas in the Mercator part of the grid and separate polar regions
• Time window for profile assimilation: -12 days to +12 hours
• MODAS is a U.S. Navy product and is not available for public distribution

Operational Details

TBA

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.

(Cummings and Smedstad, 2013)

J. A. Cummings and O. M. Smedstad. 2013: Variational Data Assimilation for the Global Ocean. Data Assimilation for Atmospheric, Oceanic and Hydrologic Applications vol II, chapter 13, 303-343.

(Cummings, 2005)

Cummings, J.A., 2005: Operational multivariate ocean data assimilation. Quart. J. Royal Met. Soc., Part C, 131(613), 3583-3604.

(Fox et al., 2002)

Fox, D.N., W.J.Teague, C.N. Barron, M.R. Carnes, and C.M. Lee, 2002. The Modular Ocean Data Assimilation System (MODAS). J. Atmos. Ocean. Technol., 19, 240-252.