Abstract/Summary

Polar lows (PLs) are intense maritime mesoscale cyclones that often form during marine cold air outbreaks. The objective of this study is to determine the atmospheric model horizontal resolution needed to correctly represent PLs for climate modelling. Three simulations have been conducted with the Weather Research and Forecasting (WRF) model using grid spacings of 50, 25 and 12.5 km. PLs have been tracked using a combination of objective and subjective tracking methods. The number of PLs detected in each simulation increases, and their average equivalent radius decreases, as the model resolution increases. A comparison against three PL track climatologies shows that the hit rate increases with increasing resolution of the atmospheric model. The lifetime maxima of the area-maximum 10-m wind speed and area-average surface sensible heat fluxes associated with PLs are on average 12% and 20% larger, respectively, in the higher-resolution simulations than in the lower-resolution one. The lifetime maximum of the area-maximum 1-h accumulated precipitation is 67% and 133% larger in the 25- and 12.5-km simulations, respectively, than in the lower-resolution one. We conclude that a better representation of PLs can be obtained by increasing the resolution of atmospheric models from 50 to 25 km, but further increasing the resolution to 12.5 km will not result in a substantial improvement.