The ACCIMA Project — Coupled Modeling of the High Southern Latitudes

The Atmosphere-ocean Coupling Causing Ice Shelf Melt in Antarctica (ACCIMA) collaborative project combines a team of researchers at The Ohio State University (OSU), New York University (NYU), and Old Dominion University (ODU) to model the multi-disciplinary processes impacting the Antarctic Ice Sheet. Understanding the mass balance of the Antarctic Ice Sheet is critical for projecting global sea-level change. The Antarctic Ice Sheet also responds to climate phenomena with signatures on the decadal time scale, such as the El Niño-Southern Oscillation, the Southern Annular Mode, and the Pacific Decadal Oscillation. Important mesoscale phenomena in the atmosphere and ocean deliver heat to the bottom of the floating Antarctic ice shelves, such as those in the Amundsen Sea embayment. Therefore, a mesoscale approach is required to treat the system processes that melt Antarctic ice shelves. While recent work in the climate modeling community has emphasized coupling of multiple components so as to achieve flexible, quantitative, multi-disciplinary tools to address the various critical climate questions, global models are not ideal to treat driving processes on the mesoscale. Consequently, we adopt a high-resolution regional climate approach to modeling the key coupled atmosphere-ocean-ice processes for the Antarctic Ice Sheet with an initial regional emphasis on the West Antarctic and Amundsen Sea.

The primary tool for the project will be a coupled modeling system including the Polar-optimized Weather Research and Forecasting model (Polar WRF) for the atmosphere, the Regional Ocean Modeling System (ROMS) for the ocean, and the Los Alamos sea ice model (CICE) for sea ice. A thermodynamic ice shelf model that is already part of ROMS is included. Retrospective decadal simulations will be performed to understand recent past variability. Downscaled future projections for Antarctica will be driven by the global National Center for Atmospheric Research (NCAR) Community Earth System Model (CESM or its equivalent). Upon project completion we will assess the feasibility of further advancing this regional modeling effort. If our downscaled hindcast and forecast regional model simulations are evaluated to be an improvement over coarse-resolution modeling, we would in the future propose to include an interactive ice sheet into our coupled system so as to freely evolve the ice sheet and thereby make quantitative projections of sea level change.

Work on the coupled modeling system is still underway, but we already have a coupled atmosphere/sea-ice/ocean (although the current ocean model is the Parallel Ocean Program model with no ice shelves) model running at 30 km resolution on a common model grid that covers the continent and extends out over the entire Southern Ocean up to at least the Subantarctic Front. We also have a separate ocean-sea ice-ice shelf model, using ROMS, running at 10 km resolution over the same domain as the coupled modeled and preliminary results from both resolution domains will be presented.