Giersch, Sebastian
[VerfasserIn]
;
Raasch, Siegfried
[MitwirkendeR]
High resolution numerical simulations of dust devils in the convective boundary layer – effects of detailed process representation on Vortex development and dust release
- [published Version]
Titel:
High resolution numerical simulations of dust devils in the convective boundary layer – effects of detailed process representation on Vortex development and dust release
Beteiligte:
Giersch, Sebastian
[VerfasserIn]
Erschienen:
Hannover : Institutionelles Repositorium der Leibniz Universität Hannover, 2024
Anmerkungen:
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Beschreibung:
Dust Devils (DDs) are convective whirlwinds that frequently occur in the atmospheric Convective Boundary Layer (CBL) of arid regions during daytime. If strong enough, they transport soil particles into the atmosphere. These aerosols alter cloud microphysics and the Earth’s radiation budget. Existing quantifications of the particle release and estimates of the contribution of DDs to the local, regional, and global dust cycle are highly uncertain. Good knowledge about the DD statistics and dynamics would help to improve them. A better understanding of DDs is also beneficial for investigations of other vortex types like tornadoes or waterspouts. This thesis presents results from numerical investigations of DD-like vortices that occur in CBLs. The simulations are carried out with the turbulence-resolving PALM model system. The first study investigates the effects of the grid spacing, background wind, and surface heat flux heterogeneities on the DD characteristics with a focus on the vortex strength. It is shown that grid spacings of 2 m, a striped pattern of heat flux heterogeneities, and moderate background winds significantly increase the vortex strength in Large-Eddy Simulation (LES) of the atmospheric CBL. These are the first numerical simulations that have ever produced DD-like vortices of observed intensity. In the second study, DD-like vortices are investigated in Direct Numerical Simulation (DNS) of Rayleigh-Bénard convection for Rayleigh numbers up to 10 to the power of 11 for the first time. The model domain’s aspect ratio, the velocity boundary condition, and the Rayleigh number are the main control parameters that are varied. It is shown that a minimum Rayleigh number of 10 to the power of 7 is necessary for the development of DD-like vortices, which is much less than a typical atmospheric value of 10 to the power of 18. While the aspect ratio shows only minor effects on the vortices, the Rayleigh number and surface friction are critical parameters for nearly all vortex properties. The results also ...