Improved representation of extratropical cyclone structure in HighResMIP models

Abstract

General circulation models are broadly able to capture the shape and structure of extratropical cyclones. Increased atmospheric resolution has been shown to improve the representation of cyclone structure. However, the intensity of cyclones, and the strength of their winds, are commonly underestimated in models. Using a cyclone compositing technique applied to the new generation HighResMIP and CMIP6 models, the representation of cyclone wind speeds and airstreams is quantified. CMIP6 models are able to capture the structure of cyclones, however winds associated with various airstreams within the cyclones are too weak. HighResMIP models show considerable improvements, with a majority of cyclone-scale biases present in the CMIP6 models reduced in both winter and summer seasons in the Northern and Southern hemispheres. HighResMIP and CMIP6 models have similar biases on the large-scale, with both struggling to represent the width of the upper-level jet.