Competing radiative impacts of low-level and high-level clouds on the strength of an idealized extratropical cyclone

Extratropical cyclones are the main driver of everyday weather in the midlatitudes. These cyclones are known to be affected by latent heating and are a popular subject of research regarding possible changes in a warming climate. In contrast, the role of radiation - and especially the radiative impact of clouds - in shaping extratropical cyclones has hardly been investigated. To study how cloud-radiative heating of the atmosphere might impact cyclones, we present idealized baroclinic life cycle simulations with the global atmosphere model ICON-NWP in aquaplanet setup with prescribed sea surface temperatures. Several simulation setups are used to isolate not only the overall cloud-radiative impact but also the impacts of low-level clouds and high-level clouds. Moreover, the cloud-radiative impact is compared between two model versions, ICON 2.1 and ICON 2.6. While the model versions simulate similar cyclones when radiation is not taken into account, enabling cloud-radiation interaction leads to contradicting effects.In ICON 2.1 clouds lead to a weakening of the cyclone magnitude by 15%, whereas in ICON 2.6 they strengthen the cyclone by 7%. The different cloud impact results from a robust competition between the radiative impact of low-level clouds, which in both model versions weaken the cyclone, and high-level clouds, which in both model versions strengthen the cyclone. The difference in the overall cloud-radiative impact between the two model versions results from the fact that ICON 2.1 simulates much more low-level clouds than ICON 2.6. This shows that the vertical distribution of clouds and their radiative heating can be an important factor for the dynamics of extratropical cyclones.