Sensitivity experiments for polar low forecasting with the CMC mesoscale finite‐element model

Abstract High?resolution versions of the Canadian operational regional finite?element model (RFE) have been developed to assess their potential in simulating mesoscale, difficult?to?forecast and potentially dangerous weather systems commonly referred to as polar lows. The operational (1989) 100?km version and a 50?km version of the model have been run for two different polar low cases: one over Hudson Bay and one over Davis Strait. More integrations have also been performed on the Hudson Bay event both at 50 and 25 km to assess the model sensitivity to ice cover. As expected, the reduction in spatial truncation errors provided by the increase in resolution results in a better simulation of the systems. Moreover, when run at higher resolutions the model shows a significant sensitivity to ice cover. The results of the ice?cover experiments also put into perspective the interaction between the heat and moisture fluxes at the surface, the low?level wind structure, and the relation of these to the development of the polar low. This study suggests that the improved forecast accuracy obtained from increased resolution is limited by the correctness of the analysis of the ice cover, which acts as a stationary forcing for the entire forecast period.