Measurements of Martian Dust Devil Winds with HiRISE

TL;DR

This study uses HiRISE observations to measure wind speeds within Martian dust devils, revealing circulatory motion, wind speeds up to 30 m/s, and insights into their vortex structure, which impacts dust lifting processes.

Contribution

It provides the first detailed wind measurements within Martian dust devils using high-resolution imaging and tests the Rankine vortex model against observed velocity profiles.

Findings

Dust devil winds reach 20-30 m/s.

Radial velocity profiles partly support the Rankine vortex model.

Dust devils can cause a 1% pressure decrease, aiding dust lifting.

Abstract

We report wind measurements within Martian dust devils observed in plan view from the High Resolution Imaging Science Experiment (HiRISE) orbiting Mars. The central color swath of the HiRISE instrument has three separate charge-coupled devices (CCDs) and color filters that observe the surface in rapid cadence. Active features, such as dust devils, appear in motion when observed by this region of the instrument. Our image animations reveal clear circulatory motion within dust devils that is separate from their translational motion across the Martian surface. Both manual and automated tracking of dust devil clouds reveal tangential winds that approach 20-30 m/s in some cases. These winds are sufficient to induce a ~1% decrease in atmospheric pressure within the dust devil core relative to ambient, facilitating dust lifting by reducing the threshold wind speed for particle elevation. Finally, radial velocity profiles constructed from our automated measurements test the Rankine vortex model for dust devil structure. Our profiles successfully reveal the solid body rotation component in the interior, but fail to conclusively illuminate the profile in the outer regions of the vortex. One profile provides evidence for a velocity decrease as a function of r^-1/2, instead of r^-1, suggestive of surface friction effects. However, other profiles do not support this observation, or do not contain enough measurements to produce meaningful insights.