Declining Sea Ice and Its Relationship with Arctic Cyclones in Current and Future Climate Part I: Current Climatology in CMIP6 Models

Abstract. The Arctic climate system is changing rapidly. These large changes will have implications in the Arctic and beyond. One of the main components of the Arctic climate system are Arctic cyclones. The strong coupling between the sea ice and Arctic cyclones makes it an important topic in the warming climate. In this study, an ensemble of CMIP6 model output was utilized from 1985–2014, to determine how well the chosen models depict Arctic cyclones and their relationship with sea ice. A comprehensive climatology of Arctic cyclones and sea ice concentrations (SIC) was provided based on selected models from5 CMIP6 and the results were compared to the ERA5 product. The model results did closely match reanalysis data in depicting the observed sea ice trend. However, we found that the model results struggled to reproduce the strongly coupled relationship between the declining sea ice and Arctic cyclones. The local cyclogenesis in the Arctic was shown to be underestimated, which led to an overall underestimation of Arctic cyclones in the CMIP6 model results. The results also showed differences between model results and ERA5 with regard to cyclone intensities. The the magnitude and sign of the intensity differences varied based10 on the nominal resolution of the model, their surface roughness parametrization and cyclogenesis location.