2012 Seasonal Forecasts Using the Navy's Arctic Cap Nowcast/Forecast System

As conditions in the Arctic continue to change, the Naval Research Laboratory (NRL) has developed an interest in longer-term seasonal ice extent forecasts. The Arctic Cap Nowcast/Forecast System (ACNFS), developed by the Oceanography Division of NRL, was run in forward model mode, without assimilation, to estimate the minimum sea ice extent for September 2012. The model was initialized with varying assimilative ACNFS analysis fields (June 1, July 1, August 1 and September 1, 2012) and run forward for nine simulations using the archived Navy Operational Global Atmospheric Prediction System (NOGAPS) atmospheric forcing fields from 2003-2011. The mean ice extent in September, averaged across all ensemble members was the projected summer ice extent. These results were submitted to the Study of Environmental Arctic Change (SEARCH) Sea Ice Outlook (SIO) project (http://www.arcus.org/search/seaiceoutlook). Results show predicted sea extents ranging from 4.29 – 4.76 M km2 with standard deviations of 0.4-0.6 M km2 for the June – August SIO estimates. The Arctic recorded an all-time record minimum sea extent of 3.41 M km2 on September 16. A special run was performed with an initialization on August 15, 2012 after a significant storm in the Beaufort Sea in early August caused an expanded area of ice free conditions. With this August 15 initialization we recorded a minimum sea ice extent of 3.43 M km2 +/- 0.26 M km2. The ACNFS is a ~3.5 km coupled ice-ocean model that produces 5 day forecasts of the Arctic sea ice state in all ice covered areas in the northern hemisphere (poleward of 40° N). The ocean component is the HYbrid Coordinate Ocean Model (HYCOM) and is coupled to the Los Alamos National Laboratory Community Ice CodE (CICE) via the Earth System Modeling Framework (ESMF). The ocean and ice models are run in an assimilative cycle with the Navy's Coupled Ocean Data Assimilation (NCODA) system. Currently the ACNFS is being transitioned to operations at the Naval Oceanographic Office.