Recent Improvements to US Navy Sea Ice Coupled Modeling Systems Using High-Resolution Data

There are two concurrent Navy coupled ocean and sea ice models: the operational Arctic Cap Nowcast/Forecast System (ACNFS), covering the Northern Hemisphere poleward of 40⁰N, and the pre-operational Global Ocean Forecast System (GOFS 3.1), a fully global system. The ice component of the coupled systems is the Community Ice Code (CICE), developed at Los Alamos National Laboratory. It is fully coupled to the HYbrid COordinate Model (HYCOM), developed by the HYCOM consortium, via the Earth System Modeling Framework. Polar resolutions are approximately 3.5 km, while resolution increases to 6.5 km near 40⁰N. Atmospheric forcing is provided by the Navy Global Environment Model (NAVGEM). Navy Coastal Ocean Data Assimilation (NCODA) handles the assimilation of satellite-derived and in situ observations.

Until recently, increases in the resolution of the US Navy's sea ice models have outpaced that of some critical observations. For example, both systems initially assimilated ice concentration from the Special Sensor Microwave/Imager Sounder (SSMIS) that were more appropriate for their 25 km predecessor. In recent experiments, ice concentrations have progressed from the 25 km SSMIS to the 12.5 km Advanced Microwave Scanning Radiometer (AMSR2) to a new blended AMSR2/Interactive Multisensor Snow and Ice Mapping System (IMS) product at 4 km resolution.

ACNFS and GOFS 3.1 provide 7-day forecasts of ice concentration, thickness, drift and lead opening rate. Errors in the model ice edge, derived from ice concentration, are determined using the National Ice Center's daily analysis as a baseline. Model ice drifts are compared to velocities derived from IABP buoy position data, Woods Hole Ice-Tethered Profilers, and CRREL ice mass balance buoys. Finally, model ice thicknesses are compared to IceBridge flight data and CRREL ice mass balance buoy observations.