Future changes to extra-tropical cyclones: combining CMIP6 projections and idealised modelling.

Extra-tropical cyclones (ETCs) are an important part of the climate system and are responsible for much of the weather in the mid-latitudes. The most extreme of these weather systems can cause damaging winds and heavy precipitation and can have adverse impacts on society. While the current generation of climate models are starting to agree on how the number, intensity and location of ETCs will change in the future, considerable uncertainty remains in how impact-relevant parameters such as wind gusts and precipitation will change. Here we use a novel combination of CMIP6 model projections and idealised model simulations of baroclinic waves to identify how precipitation and 10-m winds and wind gusts associated with ETCs may change in the future. We have performed a large ensemble (~6500 members) of baroclinic life cycle simulations with OpenIFS, which is a version of ECMWF’s Integrated Forecast System. The ensemble was created by varying 7 parameters with Latin hypercube sampling: average surface temperature; surface relative humidity; jet width, height and strength; lapse rate; and surface roughness. CMIP6 projections indicate an increase in mean temperature, lapse rate, jet width, and upper-level jet wind strength, and little change in relative humidity, jet height or surface roughness. Using CMIP6 projections from different scenarios, we map future climate projections onto the same 7-dimensional parameter space and thus identify the baroclinic wave simulations which are closest to the mean background states predicted in CMIP6 in the future. As our baroclinic wave simulations produce considerably more output fields at much higher temporal resolution compared to CMIP6, this approach enables a more thorough approach for examining how ETCs, and in particular, their precipitation and wind gusts, will change in the future. Initial results from this analysis will be presented.