LES of dust devils
Responsible: Theres Riechelmann geb. Franke
Project type: Diplomarbeit (equivalent to master thesis)
Duration: 01/09/2006 - 31/08/2007

The objective of this project is to analyze dust devils in the atmospheric boundary layer using LES, particularly regarding to its thermodynamical structure, formation mechanism and dependency of dust devil characteristics on atmospheric conditions.

Dust devils are particle loaded vertical convective vortices in the convective boundary layer. They are characterized by high rotating wind speeds, significant electrostatic fields, and by reduced pressure and enhanced temperature at their centers. Convective vortices can be found on Earth and Mars and are formed as a result of vertical instability in the atmosphere (e.g. due to ground heating by strong insolation), wherever a superadiabatic atmospheric lapse rate, a source of vorticity and a supply of sand, dust or debris are present.

Although there has been more than one century of investigations about dust devils, the knowledge of dust devils is still limited. Former investigations were focused, beside the structure and characteristics of dust devils, at impacts on convection, arid zone erosion and sediment transport. Furthermore theoretical vortex models were developed and compared with observations and laboratory simulations of dust devils. Since a couple of years there also has been LES studies of dust devils. Kanak et al. (2005) likely produced the first LES of dust devil-scale vortices on Earth that had physical characteristics in reasonable agreement with observations. But they also located some limitations and open questions during their work. Within this project it is now tried to analyze and solve some of these and former questions. For those purposes we planned a simulation which resolves the relevant large-scale turbulent structures of the atmospheric boundary layer and the small-scale dust devil itself simultaneously for the first time.

An animation of a dust devil can be found in our gallery.

Project-related Publication:

• Raasch, S. and T. Franke, 2011: Structure and formation of dust devil-like vortices in the atmospheric boundary layer: A high-resolution numerical study. J. Geophys. Res., 116, D16120, doi:​10.1029/2011JD016010.