Head
Siegfried Raasch
Small-scale, rather short-lived convective vortices with a vertical axis of rotation, which appear by swirling up particles such as dust, are called dust devils. This phenomenon especially occurs over dry ground during high-pressure weather conditions with low to moderate background winds and strongly over-adiabatic temperature gradients on the ground.
Besides their visually impressive appearance, dust devils are particularly interesting because of their influence on the vertical boundary layer transport of, for example, dust or heat. In addition, wind speeds of more than 10 m s-1 and sudden changes in wind direction caused by dust devils lead to a hazard for the environment, for example for air traffic. Therefore, these vortices have been intensively observed, measured and investigated experimentally or numerically since the 20th century. In addition to characteristic features such as diameter, height or lifetime, this study focuses on the formation and maintenance of dust devils. The quantification of their vertical transports plays also an important role in order to better assess the significance of dust devils for the weather and climate.
In these research areas, the project, which is funded and peer-reviewed by the German Research Foundation (DFG), aims to provide new insights and to support or refute theories that have been established so far. This is being done in cooperation with the Ilmenau Fass working group of the Ilmenau University of Technology, which is responsible for the experimental research work. The numerical investigations are carried out from Hanover with the help of the large-eddy simulation model PALM (PArallelized Large-eddy simulation Model), which has been developed at the Institute of Meteorology and Climatology and which enables turbulence-resolving simulations.
