The impact of changing sea ice on the mid-latitude circulationand extra-tropical cyclones

The Arctic is warming close to 4 times faster than the global average, a phenomenon known asArctic amplification. This reduces the meridional temperature gradient, sea-ice concentration, andbaroclinicity in the lower atmosphere. How these changes to the large-scale environment impact thenumber and intensity of mid-latitude cyclones remain unclear. We hypothesise that the extraction ofavailable potential energy by extra-tropical cyclones (ETCs) - known as eddy efficiency - is impactedby Arctic amplification and contributes to changes in ETC count, intensity, and deepening rate.ETCs obtain their kinetic energy via various sources, for example latent heating or eddy-mean-flowinteraction. One mechanism prevalent in ETCs is the conversion of available potential energy intokinetic energy. The mechanism’s efficiency is governed by the alignment of the mean baroclinicityand eddy heat flux. This is referred to as the eddy efficiency. We hypothesise that it is affectedby changes in the polar regions. To test this, three 40-year long OpenIFS simulations are run withsea-ice concentrations and sea surface temperatures in the Arctic and Antarctic according to thecurrent climatology, the SSP126 scenario, and the SSP585 scenario. The mid-latitude circulation inboth hemispheres is examined in each experiment. We diagnose changes to the eddy heat flux, meanbaroclinicity, and atmospheric static stability individually. Moreover, we calculate the eddy efficiencyand decompose it into two terms: the tilt orientation and magnitude term. In addition, we associatethe ETC count, intensity, and deepening rate to the mid-latitude circulation characteristics.Preliminary results indicate that the jet stream weakens in climates with reduced baroclinicity. Wewill also present results showing how the number, intensity and deepening rate of ETCs, as well as theeddy efficiency change, and how the vertical and horizontal circulation structure relates to the eddyefficiency in the different simulations.