Home Data Server NAVGEM Forcing
Need support? Email This e-mail address is being protected from spambots. You need JavaScript enabled to view it
Got questions?
Email This e-mail address is being protected from spambots. You need JavaScript enabled to view it

Currently hycom.org serves several different HYCOM-ready forcing products, see http://hycom.org/dataserver. Among these are the old NOGAPS output, NCEP CFSR output and NAVGEM output. The NAVGEM directories will include a version number to differentiate the products.

NAVGEM 1.3/1.4 Print

The Naval Research Lab (NRL) - Monterey continues development of their atmospheric forecast model, the NAVy Global Environmental Model (NAVGEM). It has an aggressive upgrade schedule and in October 2016 NAVGEM 1.4 became operational, replacing NAVGEM 1.3 that replaced NAVGEM 1.2 in June 2015. Typically, FNMOC continues to run one version back from the operational version for products like the Global Ocean Forecast System (GOFS) 3.0, which switched to NAVGEM 1.3 with experiment 91.2 in April 2016, and we expect it will continue to use NAVGEM 1.3 forcing until it is decommissioned. The forthcoming GOFS 3.1 is forced by NAVGEM 1.4.

This page will not focus on physics or data assimilation changes between successive NAVGEM versions, but will simply guide the end-user of its output. The main difference is an increase in the horizontal resolution. NAVGEM 1.1 and 1.2 ran at T359L50 while NAVGEM 1.3 and 1.4 runs at T425L50. The array size is now 1280 x 640 and its effective resolution is 0.28125°. However, it is distributed on a Gaussian grid, i.e. the grid spacing is constant in longitude, but varies in latitude. The HYCOM interpolation scripts can deal with this grid and in the *.D files, DYIN = 0.0 is a marker to tell the scripts that the forcing is on a Gaussian grid.

Another notable difference with NAVGEM 1.3 and 1.4 is that the individual upward and downward components of shortwave and longwave radiation are provided, rather than simply the net quantity.

When a new version of NAVGEM is being developed, a multi-year hindcast is generally integrated (by NRL-Monterey) before the system goes operational. The temporal frequency of the hindcast output is 1-hourly but switches to 3-hourly when it is operational (and run by FNMOC). There is a small amount of overlap between the 1-hourly hindcast and 3-hourly operational output. This switch in temporal frequency may affect how you use the NAVGEM output to force HYCOM. When the temporal resolution is 1-hourly, it is sufficient to resolve the diurnal cycle of shortwave radiation. Thus, there is no time filtering done to any of the 1-hourly files. However, when the temporal frequency switches to 3-hourly, the diurnal cycle of shortwave radiation is not properly resolved and thus an anti-alias correction is applied to the shortwave component. In addition, a daily filter is applied to the shortwave and longwave fields in the four variable files (TaqaQ?Q?.D). Note that HYCOM provides an option to apply an analytic diurnal cycle to shortwave (dswflg=1), however, this should only be turned on if using daily filtered shortwave.

As with previous versions of NAVGEM, the user needs to be aware that there can be differences in the surface winds and heat fluxes between successive versions. In an attempt to mitigate this, ‘sec’ versions are made, where the ‘c’ stands for corrected. The zonal and meridional winds are calibrated against satellite scatterometer observations and the downward shortwave and longwave fields are calibrated against NASA CERES satellite data. Use ‘sec’ versions if they exist, otherwise use the ‘sea’ versions (that differ from the ‘std’ versions) that mitigate coastline mismatches between the atmospheric model’s land-sea mask and HYCOM’s land-sea mask.

The land-sea mask (navgem_0.281deg_computagrid_mask_1280x640.D) is the same for NAVGEM 1.3 and 1.4.

1-hourly hindcast output: 20131001 - 20150703
3-hourly operational output: 20150630 and continuing until it is decommissioned
1-hourly hindcast output: 20140701 - 20161031
3-hourly operational output: 20161013 and continuing until it is decommissioned

The 3-hourly files are generally updated once per week (Thursday or Friday) on hycom.org.

A typical set of 1-hourly files that might be used:

mean sea level pressure (hPa/100 - 1000)
surface (land and ocean) temperature (Kelvin)
2 m specific humidity (kg/kg)
2 m air temperature (Kelvin)
total (large-scale and convective) precipitation1
upward surface longwave (W/m2)
upward surface shortwave (W/m2)
temp2m, spchum, net LW, downward SW
temp2m, spchum, net SW-LW, net shortwave
downward surface longwave (W/m2)
downward surface shortwave (W/m2)
net surface longwave (W/m2)
net surface shortwave (W/m2)
10 m zonal and meridional wind velocity (m/s)
10 m wind speed (m/s)

The units of precipitation may differ between the 1-hourly hindcast output and the 3-hourly operational output. Units are listed in the header of the *ttlpcp.D file and can be obtained with,

 wind_stat –s navgem0.281c-sea_2015_01hr_ttlpcp.D 

If the units are m/day, then PMKS = 1.1574074E-5 in the precipitation interpolation script, but if the units are cm/hr, then PMKS = 2.7777778E-6, in the precipitation interpolation script.

The 3-hourly files have the version number as part of the filename but are otherwise the same with these exceptions:

alias corrected
alias corrected
NAVGEM 1.3 only
1.3 only, 3-hourly Taqa, daily filtered QlQg
3-hourly Taqa, daily filtered QrQp
alias corrected
NAVGEM 1.4 only, alias corrected, daily filtered
alias corrected

NAVGEM 1.1/1.2 Print

* L E G A C Y *

Please use NAVGEM 1.3/1.4

The Naval Research Lab (NRL) - Monterey developed a new atmospheric forecast model, the NAVy Global Environmental Model (NAVGEM) that replaced the Navy Operational Global Atmospheric Prediction System (NOGAPS). It initially run at T359L50 resolution (with planned resolution upgrades) and has a new and improved dynamical core. NAVGEM version 1.1 was transitioned to the Fleet Numerical Meteorology and Oceanography Center (FNMOC) and completed its Operational Test in January 2013. The results show an across the board improvement in forecast skill over NOGAPS and it became the US Navy's new operational atmospheric forecast system on 13 March 2013 12Z.

NRL-Monterey and FNMOC have a very aggressive upgrade cycle for NAVGEM in which the model physics will improve and spectral resolution will increase. Currently (28 April 2014) NAVGEM 1.2 is the operational system.

The Global Ocean Forecast System (GOFS) runs daily at the Navy DoD Supercomputing Resource Center (DSRC) and currently uses NAVGEM forcing, but previously used NOGAPS forcing. Comparisons made between NOGAPS and NAVGEM showed that their surface differences were large enough that we could not simply switch products and expect the ocean model response to be unchanged. Because of these large surface heat flux and wind inconsistencies, great care was taken when switching from NOGAPS to NAVGEM. This NRL Memorandum Report details what was done in the operational GOFS to mitigate spurious upper ocean response using different atmospheric forcing.

***The user needs to be aware that there can be large differences in the surface winds and heat fluxes between successive versions of NAVGEM.***

Currently hycom.org serves several different HYCOM-ready forcing products, see http://hycom.org/dataserver. Among these are the old NOGAPS output, NCEP CFSR output and NAVGEM output. The NAVGEM directories will include a version number to differentiate the products.

The files in navgem0.5a start at various times depending upon the version and how long of a hindcast NRL-MRY ran. They do not contain any forecasts. When we process forcing products, we'll put all variables into their own files, and additionally we'll merge certain variables because that is what the interpolation code expects. For a specific year, we have these fields like:

a merged file of temp2m (air temp at 2m), spchum (specific humidity), radiative fluxes that is composed of solrad (net surface shortwave) minus longwv (net surface longwave) and penetrating radiation (solrad). This field is the input thermal forcing file for a HYCOM simulation. The fields in this file have a daily filter applied to them.
These are like the TaqaQrQp daily filtered files, but Ta and qa are NOT daily filtered whereas QrQp ARE daily filtered.
These files are used by CICE when running coupled HYCOM/CICE. Taqa are the same as in the TaqaQrQp files, but Ql is net surface longwave radiation and Qg is downward surface shortwave radiation (glbrad).
dewpoint temperature at 2 m (Kelvins)
the atmospheric model's land/sea mask
net surface longwave (W/m^2)
mean sea level pressure (hPa/100 - 1000)
surface (land and ocean) temperature (Kelvins)
net surface shortwave (W/m^2)
specific humidity (kg/kg)
bulk-derived wind stress (N/m^2)
planetary boundary layer wind stress (N/m^2)
air temperature at 2 m (Kelvins)
zonal and meridional wind components (m/s)
wind speed (m/s)

The lndsea files is actually dynamic for navgem0.5a with: 0 = OCEAN, 1 = LAND, 2 = ICE, 3 = SNOW.

Often the wind stress curl field associated with the strpbl file is very noisy so traditionally we have always used the strblk stresses to force HYCOM. Nonetheless, we keep both sets of stresses.

For the set of files listed above, there are navgem0.5a-sea versions. For the QuikSCAT corrected winds and stresses, these are the 'sec' files. Note there are secC and secD versions. For uv-10m and wndspd, the secC are the appropriate files to use but for strblk the secD file is appropriate. For simplicity, we simply call them sec (without the C or D).


FileYearAuthorsSourceFile size
Download this file (NRL MR-9486.pdf)NRL MR-9486.pdf2013Metzger,Wallcraft,Posey,Smedstad,FranklinNRL5367 Kb
Download this file (HYCOM_NAVGEM_Evaluation_Report_21AUG13.pdf)HYCOM NAVGEM Evaluation Report2013Frank BubNAVOCEANO989 Kb




This is a demonstration product from the HYCOM Consortium and is provided as is. HYCOM Consortium does not warrant or suggest that this data is fit for any particular purpose. Further, neither COAPS nor HYCOM consortium guarantee availability, service updates or timely data delivery.