|Institute for Atmospheric Physics
- Revised cloud scheme for liquid clouds within the second phase of project HD(CP)2 (High definition clouds and precipitation for advancing climate prediction)
Cloud droplets in the atmosphere usually form on aerosols. In the early stage of droplet formation, water vapor attaches on the dry aerosol and forms a wetted aerosol or haze particle. If this particle grows further above a critical mass, it called a cloud droplet. The critical mass is predicted by Köhler-theory and the transition from a haze particle into a cloud droplet is called "activation". The next stage of droplet growth in a supersaturated environment is governed by the diffusional or condensation growth, where water vapour diffuses towards the cloud droplet and condenses. In this project, we aim at a physically correct implementation of the activation and condensation process for high-resolution numerical models, as developed within the first phase of HD(CP)2. The process of droplet activation is crucial for cloud development and comprises a major part for cloud-aerosol interactions. Another part of cloud-aerosol interactions is the so-called wet scavenging of aerosol particles, i.e. if the droplets sediment out of the cloud, they remove the aerosol where they formed on. Furthermore, the falling droplets will collect other aerosol particles and smaller cloud droplets, therefore the aerosol background will be modified by the cloud. Within this project, we also consider the wet scavenging process of aerosol particles. Therefore we may simulate the cloud-aerosol interactions in a physically correct manner.
More information on HD(CP)2 is avaible here: www.hdcp2.eu
- Numerical modeling of the Wegener-Bergeron-Findeisen process within the project HD(CP)2 (High definition clouds and precipitation for advancing climate prediction)
We consider the growth or evaporation of cloud particles due to diffusion of water vapor in a mixed-phase cloud, i.e. a cloud containing liquid water droplets and ice particles. Depending on the current humidity there are three different possibilities: the droplets and ice particles both grow, both evaporate or the droplets evaporate while the ice particles grow. The last scenario is known as "Wegener-Bergeron-Findeisen process". The local spatial distribution of water vapor around a cloud particle dictates if it will grow or evaporate. This local distribution of water vapor is particularly influenced by the presence of other near cloud particles. For example, in an environment where both species of cloud particles should evaporate, an ice particle might be surrounded by evaporating droplets. These droplets enrich their neighborhood with humidity. As a result, this particular ice particle can grow. We simulate local interactions of cloud particles with a direct numerical simulation, where the coupled system of diffusion equations for water vapor and heat are solved with a finite element method on a discrete numerical grid. In order to avoid the explicit adaptation of the grid to the curved cloud particles, we employ the so-called extended finite element method. The extended finite element method consists in enriching the standard finite element space with suitable functions to capture the local behaviour of the solution.
Since it is not feasible to simulate a whole cloud with such a detailed particle model, we develop a so-called "bulk model". In a bulk model we look at the whole cloud in a statistical sense which is a widely used approach in cloud modeling. In common models, the direct interaction of the cloud particles by diffusion is neglected; they can interact only via a distant reservoir representing the environment conditions. Our bulk approach retains the interaction of ice particles with surrounding droplets.
- Further research interests
- Cloud physics
- Mathematical modelling
- Numerical schemes for ordinary and partial differential equations
- Multiscale problems
- Asymptotic analysis
- SS 2013: Exercise instructor for "Anwendung von Modellen" (Prof. Spichtinger)
- WS 2013/2014: Exercise instructor for "Atmosphärische Thermodynamik" (Prof. Spichtinger)
- SS 2014: Exercise instructor for "Anwendung von Modellen" (Prof. Spichtinger)
- WS 2014/2015: Exercise instructor for "Modellbildung" (Prof. Spichtinger)