Impact of surface parameter uncertainties on the development of a trough in the Fram Strait region


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The impacts of the sea-ice characteristics distribution, roughness, temperature and thermal conductivity on an on-ice moving trough in the Fram Strait on 7 March 2002 are investigated. The situation is simulated with the mesoscale transport and fluid model METRAS and the named characteristics are varied within the range of observational uncertainty. The test cases are evaluated against aircraft measurements performed within the ‘Fram Strait Cyclone Experiment 2002’. The model's sensitivity on the changes in sea-ice characteristics is quantified by statistical means. The strongest impacts on the near-ground temperature are found from sea-ice temperature, manifesting as an overall bias, and the positioning of the sea-ice edge, manifesting as a phase error. Only higher than natural homogenization of the sea-ice cover leads to some reduction of the amplitude error. A reduction of the sea-ice surface roughness is performed by applying an unrealistically small roughness length of z0= 1  mm. This reduces the negative wind speed bias, enhances the advection of contrasting air masses and improves the frontal sharpness. The thermal conductivity has the smallest influence. The lateral forcing taken from ‘European Centre for Medium-Range Weather Forecasts’ (ECMWF) reanalyses shows the strongest effect on the limited area model performance.