* L E G A C Y *
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.
- NAVGEM 1.3
- 1-hourly hindcast output: 20131001 - 20150703
- NAVGEM 1.3
- 3-hourly operational output: 20150630 and continuing until it is decommissioned
- NAVGEM 1.4
- 1-hourly hindcast output: 20140701 - 20161031
- NAVGEM 1.4
- 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:
- navgem0.281c-sea_2015_01hr_mslprs.D
- mean sea level pressure (hPa/100 - 1000)
- navgem0.281c-sea_2015_01hr_soiltm.D
- surface (land and ocean) temperature (Kelvin)
- navgem0.281c-sea_2015_01hr_spchum.D
- 2 m specific humidity (kg/kg)
- navgem0.281c-sea_2015_01hr_temp2m.D
- 2 m air temperature (Kelvin)
- navgem0.281c-sea_2015_01hr_ttlpcp.D
- total (large-scale and convective) precipitation1
- navgem0.281c-sea_2015_01hr_ulwsfc.D
- upward surface longwave (W/m2)
- navgem0.281c-sea_2015_01hr_uswsfc.D
- upward surface shortwave (W/m2)
- navgem0.281c-sec_2015_01hr_TaqaQlQg_nofilter.D
- temp2m, spchum, net LW, downward SW
- navgem0.281c-sec_2015_01hr_TaqaQrQp_nofilter.D
- temp2m, spchum, net SW-LW, net shortwave
- navgem0.281c-sec_2015_01hr_dlwsfc.D
- downward surface longwave (W/m2)
- navgem0.281c-sec_2015_01hr_dswsfc.D
- downward surface shortwave (W/m2)
- navgem0.281c-sec_2015_01hr_longwv.D
- net surface longwave (W/m2)
- navgem0.281c-sec_2015_01hr_solrad.D
- net surface shortwave (W/m2)
- navgem0.281c-sec_2015_01hr_uv-10m.D
- 10 m zonal and meridional wind velocity (m/s)
- navgem0.281c-sec_2015_01hr_wndspd.D
- 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:
- navgem1.x_0.281c-sea_2015_03hr_dswsfc.D
- alias corrected
- navgem1.x_0.281c-sea_2015_03hr_dswsfc_noaliascorrect.D
- navgem1.x_0.281c-sea_2015_03hr_uswsfc.D
- alias corrected
- navgem1.x_0.281c-sea_2015_03hr_uswsfc_noaliascorrect.D
- navgem1.3_0.281c-sec_2015_03hr_TaqaQlQg.D
- NAVGEM 1.3 only
- navgem1.3_0.281c-sec_2015_03hr_Taqa_day-QlQg.D
- 1.3 only, 3-hourly Taqa, daily filtered QlQg
- navgem1.x_0.281c-sec_2015_03hr_Taqa_day-QrQp.D
- 3-hourly Taqa, daily filtered QrQp
- navgem1.x_0.281c-sec_2015_03hr_dswsfc.D
- alias corrected
- navgem1.4_0.281c-sec_2015_03hr_day-dswsfc.D
- NAVGEM 1.4 only, alias corrected, daily filtered
- navgem1.x_0.281c-sec_2015_03hr_solrad.D
- alias corrected
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