Intensification of Extratropical Cyclones associated with the Polar Jet Change in the CMIP5 Global Warming Projections

The projected change in intense extratropical cyclones in the Northern Hemisphere winter due to global warming is investigated using 11 climate models from the Coupled Model Intercomparison Project Phase 5 (CMIP5). In many models, the number of intense surface cyclones (sea-level pressure below 980hPa) increases on the polar side and downstream side of the storm tracks, and the mean growth rate of the cyclones is enhanced in areas upstream of these regions, especially in the North Pacific. Around these regions, the mean growth rate is highly correlated with the upper-level zonal wind on a monthly time scale, and its projected change can be largely explained by the zonal wind change. An enhanced polar jet over the North Pacific seen in many models leads to an enhanced mean growth rate of surface cyclones, while less agreement between the models is seen over the North Atlantic.