It’s time for another storm-chasing timelapse from photographer Mike Olbinski! “Vorticity 6” focuses on supercell thunderstorms and their tornadoes. There’s billowing turbulent convection, undulating asperitas, bulging mammatus, microbursts, and more. There’s nothing like timelapse to highlight the growth, rotation, and shear involved in these storms. (Video and image credit: M. Olbinski)
Saturn’s moon Titan is a fascinating mirror to our own planet. It’s the only other planetary body with surface-level liquid lakes and seas, but instead of water, Titan’s are made of frigid ethane and methane. Like Earth, Titan has a weather cycle that includes evaporation, condensation, and rain. And now scientists have made their first observations of clouds convecting in Titan’s northern hemisphere.
Using data from both the Keck Observatory and JWST, the team tracked clouds on Titan rising to higher altitudes, a critical step in the planet’s methane cycle. This translation took place over a period of days, giving scientists modeling the Saturnian moon new insight into the seasonal behaviors of Titan’s atmosphere. (Image credit: NASA/ESA/CSA/STScI; research credit: C. Nixon et al.; via Gizmodo)
Any time a fluid under gravity has areas of differing density, it convects. We’re used to thinking of this in terms of temperature — “hot air rises” — but temperature isn’t the only source of convection. Differences in concentration — like salinity in water — cause convection, too. This video shows a special, more complex case: what happens when there are two sources of density gradient, each of which diffuses at a different rate.
The classic example of this occurs in the ocean, where colder fresher water meets warmer, saltier water (and vice versa). Cold water tends to sink. So does saltier water. But since temperature and salinity move at different speeds, their competing convection takes on a shape that resembles dancing, finger-like plumes as seen here. (Video and image credit: M. Mohaghar et al.)
Temperatures in the Arctic are rising faster than elsewhere, triggering more and more melting. Photographer Scott Portelli captured a melting ice shelf protruding into the ocean in this aerial image. Across the top of the frozen landscape, streams and rivers cut through the ice, leading to waterfalls that flood the nearby ocean with freshwater. This meltwater will do more than raise ocean levels; it changes temperature and salinity in these regions, disrupting the convection that keeps our planet healthy. (Image credit: S. Portelli/OPOTY; via Colossal)
When Voyager 2 visited Uranus and Neptune, scientists were puzzled by the icy giants’ disorderly magnetic fields. Contrary to expectations, neither planet had a well-defined north and south magnetic pole, indicating that the planets’ thick, icy interiors must not convect the way Earth’s mantle does. Years later, other researchers suggested that the icy giants’ magnetic fields could come from a single thin, convecting layer in the planet, but how that would look remained unclear. Now a scientist thinks he has an answer.
When simulating a mixture of water, methane, and ammonia under icy giant temperature and pressure conditions, he saw the chemicals split themselves into two layers — a water-hydrogen mix capable of convection and a hydrocarbon-rich, stagnant lower layer. Such phase separation, he argues, matches both the icy giants’ gravitational fields and their odd magnetic fields. To test whether the model holds up, we’ll need another spacecraft — one equipped with a Doppler imager — to visit Uranus and/or Neptune to measure the predicted layers firsthand. (Image credit: NASA; research credit: B. Militzer; via Physics World)
Power plants (and other industrial settings) often need to cool water to control plant temperatures. This usually requires cooling towers like the iconic curved towers seen at nuclear power plants. Towers like these use little to no moving parts — instead relying cleverly on heat transfer, buoyancy, and thermodynamics — to move and cool massive amounts of water. Grady breaks them down in terms of operation, structural engineering, and fluid/thermal dynamics in this Practical Engineering video. Grady’s videos are always great, but I especially love how this one tackles a highly visible piece of infrastructure from multiple engineering perspectives. (Video and image credit: Practical Engineering)
Convection cells like these are all around us — in the clouds, on the Sun, and in our pans — but we rarely get to watch them in action. Convection results from densities differing in different areas of a fluid. Under gravity’s influence, having a dense fluid over a lighter one is unstable; the dense fluid will always sink and the lighter one will rise. When that motion has to take place across a large surface area, we often end up with cells like the ones seen here.
What drives the density differences in the fluid? That depends. Often there’s a temperature difference that drives warmer fluid to rise and cool fluid to sink. But that’s not always the source of convection. Evaporating a volatile chemical — like alcohol — out of a mixture can also create the density differences needed for convection. That may be the source of the convection we see here in a mixture of paint and alcohol. (Video and image credit: W. Zhu; via Nikon Small World in Motion)
The intense heat from wildfires fuels updrafts, lifting smoke and vapor into the atmosphere. As the plume rises, water vapor cools and condenses around particles (including ash particles) to form cloud droplets. Eventually, that creates the billowing clouds we see atop the smoke. These pyrocumulus clouds, like this one over California’s Line fire in early September 2024, can develop further into full thunderstorms, known in this case as pyrocumulonimbus. The storm from this cloud included rain, strong winds, lightning, and hail. Unfortunately, storms like these can generate thousands of lightning strikes, feeding into the wildfire rather than countering it. (Image credit: L. Dauphin; via NASA Earth Observatory)
In recent years, Arctic permafrost has thawed at a surprisingly fast pace. Much of that is, of course, due to the rapid warming caused by climate change. But some of that phenomenon lives underground, where water’s unusual properties cause convection in gaps between rocks, sediment, and soil.
Water is densest not as ice but as water. This is why ice cubes float in your glass. Water’s densest form is actually a liquid at 4 degrees Celsius. For water-logged Arctic soils, this means that the densest layer is not at the frozen depth but at a higher, shallower depth. This places a dense liquid-infused layer over a lighter one, a recipe for unstable convection.
In a recent numerical simulation, researchers found that this underground convection caused permafrost to thaw much more quickly than it would due to heat conduction alone. In fact, the effects appeared in as little as one month, so in a single summer, this convection could have a big effect on the thaw depth. (Image credit: top – Florence D., figure – M. Magnani et al.; research credit: M. Magnani et al.)
Around the world, dry salt lakes are crisscrossed by thousands of meter-wide salt polygons. Although they resemble crack patterns, these structures are actually the result of convection occurring in the salty groundwater beneath the soil. I have covered the physics previously, but this new article by several of the researchers gives a behind-the-scenes glimpse of the investigation itself and how they uncovered the true explanation. (Image credit: S. Liu, see also: Physics Today)