The role of horizontal resolution for polar low simulations

Polar lows are intense mesoscale cyclones that mainly occur during the winter over the sea in polar regions. Owing to their small spatial scale with a diameter between 200 and 1000 km, simulating polar lows is a challenging task. In this study we investigated how increased resolution of a numerical weather prediction model impacts its ability to simulate polar lows. We focused on a polar low that was successfully captured by three different flights during the IPY-THORPEX field campaign in 2008. Verifying model results against campaign data showed that decreasing the horizontal grid spacing from 12 to 4 km significantly improved the simulation of the developing polar low, and a further decrease to 1 km gave further improvement. A model run with latent heating reduced to 10% indicated an extensive influence of diabatic heating in this polar low case, and we suggest that the improved model performance at higher resolution could be connected to the model's handling of convection. Additional simulations starting 24 h later showed that the initial conditions were important for the model performance, and when simulating another polar low case we found that the model failed to produce the polar low independent of the resolution. This shows that while higher resolution indeed may give improved predictions of polar lows, other factors like synoptic situation, lateral boundaries and the initial condition may also be important. Copyright © 2011 Royal Meteorological Society