KNOWN PROBLEMS:

1. The GOFS 3.1-like reanalysis (GLBb0.08-53.X) has unrealistic deep water formation in the Ryukyu Trench in the western Pacific Ocean (and possibly other locations). This was due to a bad interaction of HYCOM's hybrid grid generator where NCODA's deepest analysis level was above but "close" to the bottom depth, and to a mismatch between the HYCOM and NCODA bathymetries in this region. HYCOM's hybrid grid generator formed unrealistic warm and too saline water, although with the proper density, that pooled in the deep Trench. This led to occasional instabilities that were manifested over the entire depth of the water column.
2. A second problem of noisy sea surface height and interfaces is known to exist in the Philippine Sea in this reanalysis. Far back in the lineage of GOFS 3.1, HYCOM was initialized from climatology and layer 37 was not active in the Philippine Sea. However, HYCOM gradually "grew" this layer over the course of many years of integration and with time it grew unstable. The deep interfaces became noisy and all the way to the sea surface.

What are the major differences between GOFS 3.1 & GOFS 3.0?

System Description

This dataset is created at NRL and provided "as is".

Surface forcing is from 1-hourly National Centers for Environmental Prediction (NCEP) Climate Forecast System Reanalysis (CFSR) and Climate Forecast System Version 2 (CFSv2).

How It's Generated:

1. NRL interpolates the archive files from GLBb0.08 to GLBv0.08, 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 bilinear remapping weights).
2. Next, NRL runs archv2ncdf3z on the resulting file using the “NAVO” (NetCDF) output type (interpolated to 40 standard levels). Only five fields are provided: SSH, zonal velocity, meridional velocity, temperature, and salinity. Note: NRL writes out in-situ temperature, not potential temperature. This format also uses short_ints to store 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 24-hour model forecast as a first guess in a 3D variational scheme and assimilates available satellite altimeter observations, satellite, and in-situ sea surface temperature as well as in-situ vertical temperature and salinity profiles from XBTs, Argo floats and moored buoys. Surface information is projected downward into the water column using Improved Synthetic Ocean Profiles (Helber et al., 2013).

Detailed Information

Run configuration (blkdat.input): contains model run configuration information such as time steps, advection scheme, mixed layer submodel, vertical structure, etc.

Model bathymetry (depth_GLBb0.08_??.[ab]): Files containing the model bathymetry on the native grid.

Computational grid (regional.grid.[ab]): Files containing the location of the model grid points.

References

(Cummings, J.A., 2005)

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

(Cummings, J.A. and O.M. Smedstad. 2013)

Cummings, J.A. 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.

(Helber, R.W., T.L. Townsend, C.N. Barron, J.M. Dastugue and M.R. Carnes, 2013)

Helber, R.W., T.L. Townsend, C.N. Barron, J.M. Dastugue and M.R. Carnes, 2013: Validation Test Report for the Improved Synthetic Ocean Profile (ISOP) System, Part I: Synthetic Profile Methods and Algorithm. NRL Memo. Report, NRL/MR/7320—13-9364.