18.2 Towards large-eddy simulations of dust devils with observed intensity: Effects of surface heterogeneities and numerics

Thursday, 12 June 2014: 4:45 PM
John Charles Suite (Queens Hotel)
Maren Weismüller, University of Cologne, Cologne, Germany; and S. Raasch and F. Hoffmann

Some important features of dust devil-like vortices simulated with large-eddy simulation (LES) still do not compare well with those of observed dust devils. One major difference lies in the minimum core pressure, where simulated values are still almost one order of magnitude smaller compared to the observed range of -250 to -450 Pa. However, most of the existing numerical results are based on idealized setups like homogeneous surface forcing, and they have often used grid spacings which did not resolve the vortices well enough.

In this study, we investigate the effects of various factors on the simulated vortex strength with high resolution LES. Using a higher-order advection scheme, high spatial resolution of 2 m, and a model setup with moderate background wind and a spatially heterogeneous surface heat flux, we are able to reproduce observed core pressures for the first time. A special focus is given to the effects that surface heat flux heterogeneities have on the vortex appearance, frequency, and strength. Vortices mainly appear along lines of horizontal flow convergence above the centers of the strongly heated patches, which is in contrast to some older observations where vortices seemed to be created along the patch edges.

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