Interaction of microphysical and dynamical timescales in orographic precipitation

The development of orographic precipitation depends on the interaction of processes which operate on different timescales. Dynamical timescales are inherent to the flow dynamics (e.g. advection timescale, timescale of instability growth) and can be distinguished from timescales governed by microphysical processes (e.g hydrometeor conversion timescale, timescale of hydrometer fallout). The interaction between these different timescales controls the development of orographic clouds and determines the orographic precipitation distribution.

So far, the relevance of dynamical and microphysical timescales for orographic precipitation has only been analyzed within the framework of linear models or with numerical models and simplified microphysics. Recent studies indicate that the interaction of these timescales may also be relevant for aerosol-cloud-precipitation interactions in orographic clouds.

The main goal of this study is to identify the important and dominant timescales for the orographic precipitation development in a state-of-the-art numerical model and to quantify their role in different dynamical and thermodynamical regimes. A further goal of this work is to investigate the effect of aerosols on the microphysical timescales and the feedbacks on the orographic precipitation distribution in warm-phase and mixed-phase clouds.

The simulations are performed with the non-hydrostatic limited-area weather prediction model COSMO at a resolution of 2 km. The microphysical processes are treated with a fully coupled aerosol-cloud microphysics parameterization following a two-moment approach.