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Improved sea ice forecasting must be based on improved model representation of coupled system processes that impact the sea ice thermodynamic and dynamic state. Pertinent coupled system processes remain uncertain and include surface energy fluxes, clouds, precipitation, boundary layer structure, momentum transfer and sea-ice dynamics, interactions between large-scale circulation and local processes, and others.
We will present results, comparisons, process-oriented diagnostics, and parameterization assessment from sea ice forecasts using a version of the Regional Arctic System Model (RASM) adapted for short-term Arctic sea ice forecasting. Specifically, cloud, atmosphere, and ocean observations for studies of atmospheric predictability, air-ocean turbulent fluxes, and sea ice conditions collected in the marginal ice zone from ship-based campaign and coastal Arctic land stations will be used. We will also outline future model improvements based on a comparison of observations that include replacing the mixed-layer ocean model with a multi-layer upper ocean model to allow for observed mixed layer variability, such as storing heat below the surface layer that is transferred up in large storms and horizontal ocean advection.
RASM is a limited-area, fully coupled ice-ocean-atmosphere-land model. It includes the Weather Research and Forecasting (WRF) atmospheric model, the LANL Parallel Ocean Program (POP) and Community Ice Model Version 5 (CICE5) and the NCAR Community Land Model (CLMv4.5) configured for the pan-Arctic region. These components are coupled using a regionalized version of the CESM flux coupler (CPL7), which includes modifications important for resolving the sea ice pack’s inertial response to transient (i.e. weather) events.
In order to optimize the model for short-term forecasts the dynamic level ocean model has been replaced with a mixed–layer ocean model, the horizontal domain is limited to the Arctic, and all components are run with 10km horizontal resolution. This model is run with a bulk double-moment cloud microphysics scheme for droplets and frozen hydrometeors that allows both size and number of hydrometeors to vary in response to environmental conditions (Morrison et al. 2009).
Daily 5-day forecasts with RASM-ESRL were run for the 2015 freeze-up season, initialized with GFS atmosphere and AMSR2 sea ice analyses and forced by 3-hourly GFS forecasts at the lateral boundaries. The forecasts were delivered daily and used for guidance on the UNOLS research vessel Sikuliaq during the SeaState campaign. These daily forecasts have been validated with observations of surface fluxes and vertical profiles of cloud ice and liquid at land sites, and with observations of surface fluxes and sea ice characteristics from recent ship campaign and ice mass balance buoys. These relatively short forecasts are currently being used to validate and improve simulations of synoptic evolution, atmospheric boundary-layer structure and surface energy fluxes over sea ice and the adjacent ocean.