On the physics and numerical representation of dusty cirrus clouds in weather prediction models

• Applicant: Dr. Michael Weger
• Subject Area: Atmospheric Science
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 582284899

The primary goal of this project is to gain a better understanding of the processes involved in dust cirrus clouds, a cloud type that is still poorly understood and associated with desert dust outbreaks into the upper troposphere. The distinctive characteristics of dust cirrus clouds (large-scale extent, long lifespan, high density, convective structure) make them clearly distinguishable from ordinary cirrus clouds in satellite images. It is well known that mineral dust particles act particularly effectively as ice nuclei under the conditions of the upper troposphere, and thus dust cirrus clouds also exhibit a particularly high density of ice particles. Furthermore, the altered cloud microphysics also influences the thermodynamic and dynamic conditions as well as the radiative properties of the cloud shield, leading to the development of the described cloud characteristics (e.g., convection). However, a deeper understanding of these relationships between the processes at the microscale and the macroscopic cloud properties is still lacking. For this reason, common numerical weather forecast models also exhibit large uncertainties in the prediction of dust cirrus clouds, which is usually reflected in a large-scale overestimation of solar radiation at ground level. Using high-resolution numerical simulations, the formation mechanism of dust cirrus clouds will first be elucidated under idealized conditions. These simulations will consider all important microphysical processes influenced by mineral dust. The high model resolution allows for an explicit representation of the turbulent mixing driven by atmospheric instability, the effects of which on subsequent cloud growth will be investigated. In particular, the influence of different initial conditions will be characterized. A further model uncertainty lies in the cloud microphysics schemes used. Common simplified schemes are based on a fixed particle size distribution for cloud ice, which, however, could prove too imprecise for the specific conditions within dust cirrus clouds. Therefore, a more detailed microphysics scheme, which allows for a flexible particle size distribution, will also be applied. The results and insights gained from the idealized numerical simulations will ultimately be transferred to the simulation of real-world cases. This will be demonstrated based on the simulation of a selected case and through extensive validation of model results with remote sensing observational data.

• DFG Programme: Research Grants