Regensburg 2013 – wissenschaftliches Programm

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DY: Fachverband Dynamik und Statistische Physik

DY 29: Focus Session: Rayleigh Benard System and Convective Turbulence

DY 29.4: Hauptvortrag

Donnerstag, 14. März 2013, 16:30–17:00, H44

Cloud formation studies in moist Rayleigh-Benard convection — •Jörg Schumacher — TU Ilmenau, Ilmenau, Germany

Conditionally unstable convection occurs when the stratification is stable for unsaturated air parcels but unstable for saturated air parcels. This leads to the development of isolated convective plumes or clouds which are separated by an extended unsaturated dry environment. Here the statistical behavior of conditionally unstable convection is studied in a model of moist turbulent convection with a simplified thermodynamics of cloudy air. It is closely related to the classical Rayleigh-Benard dry convection problem, but includes phase transitions between the gaseous and liquid phase and the effect of latent heat release on the buoyancy of air parcels. We demonstrate that this simplified model is not only capable to simulate cloud formation processes, but also indicates that the complex dynamics of moist convection results in the emergence of new convective regimes that do not exist in the absence of phase transition. The transition to self-aggregated convection is however highly sensitive to the diffusivity and viscosity used in the model, with the aspect ratio necessary for the transition increasing as the viscosity and diffusivity are decreased. In addition, it is also found that conditionally unstable moist convection is inefficient at transporting energy. We argue that this weak energy transport is tied to the presence of a diffusive layer near the lower boundary, which remains present even when the diffusivity is small. Furthermore, we investigate the impacts of radiative cooling on the self-sustained convective regimes.