Maintaining Consistency in the Atmospheric Forcing Applied to U.S. Navy Ocean and Ice Prediction Systems
Maintaining Consistency in the Atmospheric Forcing Applied to U.S. Navy Ocean and Ice Prediction Systems
Abstract:
The Global Ocean Forecast System (GOFS) and Arctic Cap Nowcast/Forecast System (ACNFS) are the
U.S. Navy’s operational ocean and ice prediction systems (respectively) running daily at the Naval
Oceanographic Office. They provide nowcasts through 7-day forecasts of the ocean and ice environment to
support fleet operations. These systems use atmospheric forcing provided by the U.S. Navy’s operational
numerical weather prediction (NWP) system run daily at the Fleet Numerical Meteorology and
Oceanography Center (FNMOC). Over the past few years, the NWP systems at FNMOC have undergone
a rapid upgrade process in terms of improved models physics and spectral resolution, and this is scheduled
to continue over the next several years. Prior to 13 March 2013, GOFS and ACNFS used Navy Operational
Global Atmospheric Prediction System (NOGAPS) forcing, but now use NAVy Global Environmental
Model (NAVGEM) atmospheric forcing. Significant differences in the 10 meter winds and surface heat
fluxes were found between NOGAPS and NAVGEM, and between successive versions of NAVGEM.
These differences are large enough to have an impact on the upper ocean and ice forecasts made by GOFS
and ACNFS. To mitigate the discontinuities in the ocean and ice systems when changing atmospheric
forcing, 10 m wind speed is calibrated against satellite scatterometer data and net heat flux is calibrated so
as to reduce 5-day forecast SST error. These calibrations are computed through a sequence of hindcasts and
forecasts that will be described. Overall, the methodology is shown to be effective in minimizing upper
ocean and ice discontinuities when switching from one atmospheric product to another.
U.S. Navy’s operational ocean and ice prediction systems (respectively) running daily at the Naval
Oceanographic Office. They provide nowcasts through 7-day forecasts of the ocean and ice environment to
support fleet operations. These systems use atmospheric forcing provided by the U.S. Navy’s operational
numerical weather prediction (NWP) system run daily at the Fleet Numerical Meteorology and
Oceanography Center (FNMOC). Over the past few years, the NWP systems at FNMOC have undergone
a rapid upgrade process in terms of improved models physics and spectral resolution, and this is scheduled
to continue over the next several years. Prior to 13 March 2013, GOFS and ACNFS used Navy Operational
Global Atmospheric Prediction System (NOGAPS) forcing, but now use NAVy Global Environmental
Model (NAVGEM) atmospheric forcing. Significant differences in the 10 meter winds and surface heat
fluxes were found between NOGAPS and NAVGEM, and between successive versions of NAVGEM.
These differences are large enough to have an impact on the upper ocean and ice forecasts made by GOFS
and ACNFS. To mitigate the discontinuities in the ocean and ice systems when changing atmospheric
forcing, 10 m wind speed is calibrated against satellite scatterometer data and net heat flux is calibrated so
as to reduce 5-day forecast SST error. These calibrations are computed through a sequence of hindcasts and
forecasts that will be described. Overall, the methodology is shown to be effective in minimizing upper
ocean and ice discontinuities when switching from one atmospheric product to another.