Projected Future Changes in Bomb Cyclones by the HighResMIP-PRIMAVERA Multimodel Ensemble

Bomb cyclones, or explosive cyclones, are rapidly-intensifying extratropical weather systems that are often associated with extreme wind and precipitation. The projection of bomb cyclones is crucial for climate change risk assessment given their severe impacts on society and environment. This study investigates the projected changes in bomb cyclone activity between historical (1950-2014) and future (2015-2050) periods using the HighResMIP-PRIMAVERA multimodel ensemble. In the North Pacific (NP), the ensemble projects a 0.40° northward shift of bomb cyclone activity, with a notable decrease in bomb cyclone frequency around Japan. An eastward shift of bomb cyclone activity is projected in the North Atlantic (NA) with an 11.4% decline in frequency in the northwestern NA. In the Southern Hemisphere (SH), bomb cyclone activity is projected to shift poleward by 0.49°, with little overall change in frequency. In all three analysis regions, the projected changes in bomb cyclone activity are associated with changes in lower-tropospheric baroclinicity, with the major contributor being vertical wind shear in the NP and NA and static stability in the SH. Furthermore, we identify close relationships between the projected bomb cyclone changes and mean-flow changes in the NP and SH, with the shift of mid-latitude jet latitude significantly correlated with the projected decline and poleward shift of bomb cyclone activity. In the SH, the cooling of the polar lower stratosphere also contributes to the projected poleward movement. These results are not strongly dependent on model horizontal resolution, although higher-resolution models generally have a larger number of bomb cyclones.