Ocean Ensemble Forecast Skill of the US Navy’s Extended-Range Global Prediction System

Clark David Rowley1, Prasad G Thoppil1, Patrick J Hogan1, Neil P Barton2 and Carolyn A. Reynolds2, (1)US Naval Research Laboratory, Ocean Sciences Division, Stennis Space Center, MS, United States, (2)US Naval Research Laboratory, Marine Meteorology Division, Monterey, CA, United States
The U. S. Navy is developing a fully coupled global ensemble forecast system using the Navy Global Environmental Model (NAVGEM), the HYbrid Coordinate Ocean Model (HYCOM), and the Los Alamos Community Ice CodE (CICE). This system is being developed to meet Navy needs for high-resolution global environmental forecasts on timescales from weeks to months. The initial operational capability for 2020 includes weekly extended-range 60-day forecasts of 16 members with 37 km atmospheric resolution, 1/12° ocean and sea ice resolution, and 1/4° wave model resolution. The ensemble is generated using perturbed observations in the atmosphere, ocean, and ice data assimilation.

A year-long hindcast of weekly 60-day ensemble forecasts was completed and the forecast skill of the HYCOM mean and ensemble were assessed using verifying in situ surface and profile observations. The ocean ensemble spread shows some ability to distinguish forecast errors, but is limited due to the small ensemble size. For the ensemble mean, the global average ship-based sea surface temperature (SST) root mean square error (RMSE) is more skillful than climatological estimates for the entire 60 day forecast period, and ocean subsurface temperature / salinity forecast RMSE averaged from 8 to 500 meters is more skillful than climatology to 30 days for temperature (26 days at 100 m) and 20 days for salinity.