The Switchover from NOGAPS to NAVGEM 1.1 Atmospheric Forcing in GOFS and ACNFS

The Navy Operational Global Atmospheric Prediction System (NOGAPS) has recently (13 March 2013 12Z) been replaced by the NAVy Global Environmental Model (NAVGEM) as the U.S. Navy s operational atmospheric forecast system. NOGAPS will be decommissioned on 31 August 2013 but before that date both the Global Ocean Forecast System 3.01 and Arctic Cap Nowcast/Forecast System must switch from using NOGAPS to NAVGEM atmospheric forcing. Calibrations to the wind velocities and net heat flux are performed. Wind velocities are calibrated against satellite scatterometer data whereas heat flux is calibrated using 5-day forecast SST error. The sequence of hindcasts and forecast simulations are described with the net impact of reducing 5-day forecast SST error and ice concentration error in the NAVGEM 1.1-forced system, compared to the NOGAPS-forced system. Overall, the methodology is shown to be effective in minimizing upper ocean discontinuities when switching from one atmospheric product to another.