ICON simulations of cloud diabatic processes in the warm conveyor belt of North Atlantic cyclone Vladiana

• Main Authors: Choudhary, Anubhav, Voigt, Aiko
• Format: Text
• Language: English
• Published: 2022
• Subjects: North Atlantic
• Online Access: https://doi.org/10.5194/wcd-2022-7; https://wcd.copernicus.org/preprints/wcd-2022-7/

Warm conveyor belts are important features of extratropical cyclones and are characterized by active diabatic processes. Previous studies reported that the simulation of extratropical cyclones can be strongly impacted by horizontal model resolution. Here, we study to what extent and in which manner simulations of warm conveyor belts are impacted by model resolution. To this end we investigate the warm conveyor belt of the North Atlantic cyclone Vladiana that occurred around 23 September 2016 and was observed as part of the North Atlantic Waveguide and Downstream Impact Experiment. We analyze a total of 18 limited-area simulations with the ICOsahedral Nonhydrostatic model run over the North Atlantic that cover a range of horizontal resolutions from 80 to 2.5 km, including the resolution of current low-resolution global climate models with parametrized convection as well as the resolution of future storm-resolving climate models with explicit convection. The simulations also test the sensitivity with respect to the representation of convection and cloud microphysics. With higher resolution, the number of WCB trajectories increase systematically and a new class of anticyclonic trajectories emerges that is absent at the lowest resolution of 80 km. WCB trajectories ascend faster and higher as resolution is increased. Explicitly resolving convection increases these changes further. We also diagnose the impact of increased resolution on the ascent velocity and vorticity of WCB air parcels and the diabatic heating that these parcels experience. With increasing resolution, ascent velocity increases at all pressure levels by around a factor of 3 and vorticity increases similarly strongly in the lower and middle troposphere. We find a corresponding increase in diabatic heating as resolution is refined, arising mainly from cloud associated phase changes of water. Besides resolution, the treatment of convection has a stronger impact than the treatment of cloud microphysics in our simulations. We find no clear connection between the strength of diabatic heating within the WCB on the one hand and the deepening of cyclone Vladiana in terms of its central pressure on the other hand. An analysis of the pressure tendency equation shows that this is because diabatic heating plays a minor role for the deepening of the cyclone, which is dominated by temperature advection.