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Abstract:
Extratropical cyclones are typically associated with an elongated band of mixed-phase clouds, capped with a cirrus shield that is up to 3-km deep. These large-scale cloud features, consisting of air with different origin, are associated with complex interactions with the long- and shortwave radiation. More specifically, these clouds can be produced by ascending airstreams in extratropical cyclones, the so-called warm conveyor belts (WCBs). As WCBs are considered the most cloud-producing phenomena in extratropical cyclones, it is important to understand and characterize the interaction between the clouds, radiation, and the dynamics of these airstreams. In this study, we use ERA5 reanalyses and air parcel trajectories to take a closer look at the cirrus cloud that forms at the end of the ascent of WCBs (WCB outflow). We investigate the cloud structure by determining the origin of the cloud forming air parcels and their hydrometeor history based on the trajectory calculations. The analysis shows that the WCB ice cloud exhibits a complex pattern of origins, radiative temperature tendencies and the associated modification of potential vorticity, which serves directly to analyze the impact of the cloud-related radiative heating rates on the atmospheric circulation and in particular cross-tropopause transport of humidity and atmospheric constituents. This project about extratropical cloud-radiation-circulation interactions furthers the process understanding with the help of an offline version of ECRAD, the latest radiation scheme for the ECMWF Integrated Forecast System, which we use for sensitivity analyses of how different cloud structures in WCB outflows influence the vertical profile of radiative heating.
