US Navy Operational Global Ocean and Arctic Ice Prediction Systems

Abstract

The US Navy's operational global ocean nowcast/forecast system is presently comprised of the 0.08° HYbrid Coordinate Ocean Model (HYCOM) and the Navy Coupled Ocean Data Assimilation (NCODA). Its high horizontal resolution and adaptive vertical coordinate system make it capable of producing nowcasts (current state) and forecasts of oceanic "weather," which includes three-dimensional ocean temperature, salinity, and current structure; surface mixed layer depth; and the location of mesoscale features such as eddies, meandering currents, and fronts. It runs daily at the Naval Oceanographic Office and provides seven-day forecasts that support fleet operations, provide boundary conditions to higher resolution regional models, and are available to the community. Using a data-assimilative hindcast and series of 14-day forecasts for 2012, the system is shown to have forecast skill of the oceanic mesoscale out to about 10 days for the Gulf Stream region and to 14+ days for the global ocean and other selected subregions. Forecast skill is sensitive to the type of atmospheric forcing (i.e., operational vs. analysis quality). Subsurface temperature bias is small (< 0.25°C) and root mean square error peaks at the depth range of the mixed layer and thermocline. Coupled to the Community Ice CodE (CICE) on the same grid, the HYCOM/CICE/NCODA system (initially restricted to the Arctic) provides sea ice nowcasts and forecasts. Ice edge location errors are improved from the previous sea ice prediction system but are limited in part by the accuracy of the satellite observations it assimilates.

Keywords

• HYCOM
• ocean forecast
• NCODA
• CICE
• ocean weather
• Arctic ice prediction