Wave buoy measurements at the Antarctic sea ice edge compared with an enhanced ECMWF WAM: Progress towards global waves-in-ice modelling

The breakup of pack ice in the Weddell Sea is examined with respect to a single wave buoy, frozen into the pack ice six months earlier, and the ECMWF WAM model. The pack ice broke up around the buoy on 14th September 2000 as large amplitude storm waves approached the ice edge at the buoy’s location. The WAM model is modified to allow waves to propagate into the ice cover, in contrast to the operational scheme which sets wave energy to zero at ice concentrations over 30%. A simple, lookup-table-based, wave scattering attenuation scheme is then added and is combined with a sea ice drag attenuation parameterisation. WAM results at the location of the buoy are compared to the observations over a two-month period straddling the breakup. The modified WAM scheme generally reproduces the significant wave height, wave period and spectral characteristics measured by the buoy, though the model does not yet have any concept of floe breaking and re-freezing, assuming only that the ice cover is broken if the concentration is less than 80%. The simplistic nature of these modifications is designed to allow operational implementation, to eventually provide a global assessment of the wave-influenced ice zone.