Numerical simulation of Martian dust devils

Abstract

[1] Large eddy simulations of vertical convective vortices and dust devils in the Martian convective boundary layer are presented, employing a version of the Mars MM5 mesoscale model, adapted to use periodic boundary conditions and run at resolutions of 10 to 100 m. The effects of background horizontal wind speed and shear on dust devil development are studied in four simulations, each extending over the daytime portion of one Martian day. The general vorticity development in all cases is similar, with roughly equal positive and negative vorticity extrema. Two dust devils were found to develop in the highest wind speed case and in a case run without background wind. The dust devil structures were found to agree well qualitatively with terrestrial dust devil observations, including the prediction of greatly diminished vertical velocities in the vortex core. Thermodynamic scaling theory of dust devils was found to provide good prediction of the relationship between central pressure and temperature in the modeled vortices. Examination of the turbulent kinetic energy budgets suggests balance between buoyancy generation and loss through dissipation and transport. The vorticity for the dust devils is provided by twisting of horizontal vorticity into the vertical. The horizontal vorticity originates from horizontal variations in temperature at the lower boundary (thermal buoyancy). While the horizontal winds generated by the modeled dust devils were likely insufficient to lift dust, this study provides a solid starting point for dynamic modeling of what may be an important component of the Martian dust cycle.

Dust devil speeds, directions of motion and general characteristics observed by the Mars Express High Resolution Stereo Camera

“…The dust devils seen at the front of the storm ( Figure 7b) indicate with their computed speeds as well the speed of the dust storm if they are propelled by the storm. This is supported by the simulations by Toigo et al (2003), in which dust devils developed both in the 'highest wind speed' case and in the 'no background wind' case.…”

Structure and dynamics of the convective boundary layer on Mars as inferred from large‐eddy simulations and remote‐sensing measurements

“…The last phenomenon was the focus of the Toigo et al (2003) LES study which showed similarities between the modelled vortices and the observed Martian dust devils. These preliminary results were recently confirmed by other studies (Richardson et al, 2007;Sorbjan, 2007;Spiga and Forget, 2009).…”

Quasi‐electrostatic field analysis and simulation of Martian and terrestrial dust devils

“…The formation and evolution of dust storms is a multiphysical process involving dust particle thermal and kinetic energy evolution, dust grain contact electrification and charge separation [Toigo et al, 2003;Farrell et al, 2003]. Initially, surface air molecules and dust grains absorbing heat from sunlight generate pressure and temperature gradients on the surfaces that form vertical wind or local vortices, and dust grains are lifted from the ground.…”