Interaction of microphysics and dynamics in a warm conveyor belt simulated with the ICOsahedral Nonhydrostatic (ICON) model

• Published in: Atmospheric chemistry and physics 2023-08, Vol.23 (15), p.8553-8581
• Main Authors: Oertel, Annika, Miltenberger, Annette K, Grams, Christian M, Hoose, Corinna
• Format: Article
• Language: English
• Subjects: Aerosol concentrations; Aerosols; Air currents; Air parcels; Analysis; Ascent; Atmospheric physics; Belt conveyors; Case studies; Cloud bands; Cloud droplet growth; Cloud droplets; Cloud formation; Cloud microphysics; Clouds; Condensates; Condensation; Convection; Convection heating; Conveying machinery; Cyclones; Diabatic heating; Droplets; Evaporation; Evaporative cooling; Extratropical cyclones; Freezing; Heating; Hydrometeor size; Hydrometeors; Influence; Long wave radiation; Microphysics; Potential vorticity; Precipitation; Radiation; Radiation-cloud interactions; Radiative heating; Sensitivity; Simulation; Specific humidity; Troposphere; Turbulence; Upper troposphere; Vapor deposition; Vapors; Vorticity; Warm air; Waveguides
• ISSN: 1680-7324; 1680-7316; 1680-7324
• DOI: 10.5194/acp-23-8553-2023

Warm conveyor belts (WCBs) produce a major fraction of precipitation in extratropical cyclones and modulate the large-scale extratropical circulation. Diabatic processes, in particular associated with cloud formation, influence the cross-isentropic ascent of WCBs into the upper troposphere and additionally modify the potential vorticity (PV) distribution, which influences the larger-scale flow. In this study we investigate heating and PV rates from all diabatic processes, including microphysics, turbulence, convection, and radiation, in a case study that occurred during the North Atlantic Waveguide and Downstream Impact Experiment (NAWDEX) campaign using the Icosahedral Nonhydrostatic (ICON) modeling framework. In particular, we consider all individual microphysical process rates that are implemented in ICON's two-moment microphysics scheme, which sheds light on (i) which microphysical processes dominate the diabatic heating and PV structure in the WCB and (ii) which microphysical processes are the most active during the ascent and influence cloud formation and characteristics, providing a basis for detailed sensitivity experiments. For this purpose, diabatic heating and PV rates are integrated for the first time along online trajectories across nested grids with different horizontal resolutions. The convection-permitting simulation setup also takes the reduced aerosol concentrations over the North Atlantic into account. Our results confirm that microphysical processes are the dominant diabatic heating source during ascent. Near the cloud top longwave radiation cools WCB air parcels. Radiative heating and corresponding PV modification in the upper troposphere are non-negligible due to the longevity of the WCB cloud band. In the WCB ascent region, the process rates from turbulent heating and microphysics partially counteract each other. From all microphysical processes condensational growth of cloud droplets and vapor deposition on frozen hydrometeors most strongly influence diabatic heating and PV, while below-cloud evaporation strongly cools WCB air parcels prior to their ascent and increases their PV value. PV production is the strongest near the surface with substantial contributions from condensation, melting, evaporation, and vapor deposition. In the upper troposphere, PV is reduced by diabatic heating from vapor deposition, condensation, and radiation. Activation of cloud droplets as well as homogeneous and heterogeneous freezing processes have a neg