Playful Martian Dust Devils

The Martian atmosphere lacks the density to support tornado storm systems, but vortices are nevertheless a frequent occurrence. As sun-warmed gases rise, neighboring air rushes in, bringing with it any twisted shred of vorticity it carries. Just as an ice skater pulling her arms in spins faster, the gases spin up, forming a dust devil.

In this recent footage from the Perseverance Rover, four dust devils move across the landscape. In the foreground, a tiny one meets up with a big 64-meter dust devil, getting swallowed up in the process. It’s hard to see the details of their crossing, but you can see other vortices meeting and reconnecting here. (Video and image credit: NASA/JPL-Caltech/LANL/CNES/CNRS/INTA-CSIC/Space Science Institute/ISAE-Supaero/University of Arizona; via Gizmodo)

#atmosphericScience #conservationOfAngularMomentum #dustDevils #fluidDynamics #Mars #physics #science #vorticity

Bubbly Tornadoes Aspin

Rotating flows are full of delightful surprises. Here, the folks at the UCLA SpinLab demonstrate the power a little buoyancy has to liven up a flow. Their backdrop is a spinning tank of water; it’s been spinning long enough that it’s in what’s known as solid body rotation, meaning that the water in the tank moves as if it’s one big spinning object. To demonstrate this, they drop some plastic tracers into the water. These just drop to the floor of the tank without fluttering, showing that there’s no swirling going on in the tank. Then they add Alka-Seltzer tablets.

As the tablets dissolve, they release a stream of bubbles, which, thank to buoyancy, rise. As the bubbles rise, they drag the surrounding water with them. That motion, in turn, pulls water in from the surroundings to replace what’s moving upward. That incoming water has trace amounts of vorticity (largely due to the influence of friction near the tank’s bottom). As that vorticity moves inward, it speeds up to conserve angular momentum. This is, as the video notes, the same as a figure skater’s spin speeding up when she pulls in her arms. The result: a beautiful, spiraling bubble-filled vortex. (Video and image credit: UCLA SpinLab)

#buoyancy #conservationOfAngularMomentum #flowVisualization #fluidDynamics #physics #rotatingFlow #science