During the summer months, the Barents Sea between Norway and Russia is streaked with blue and teal swirls. These beautiful patterns are the result of a phytoplankton bloom, as viewed by earth-observing satellites (with a little color enhancement). Although each cell in the bloom is only nanometers across, their collective presence is visible from space! They also act as tracers in the water, revealing the swirling flow patterns present there. (Image credit: J. Stevens/NASA Earth Observatory)
Category: Phenomena
Double Diffusive Flow
Diffusion is the tendency for differences in a fluid — in density, temperature, or concentration — to even out over time. Think about a drop of food coloring in a glass of water. Even without stirring, that dye will eventually disperse throughout the glass through diffusion. But when there is more than one factor controlling diffusion — like temperature and salinity — things get more complicated. In the ocean, for example, this double-diffusion causes salt fingers like those shown in the first image.
But what happens when the two diffusing fluid layers are flowing? That’s the question at the heart of this video, which explores the intricate mixing that takes place between doubly-diffusing liquids in a channel. (Video and image credit: A. Mizev et al.)
Brilliant Auroras
Glowing auroras billow across Canada in this satellite image from a recent geomagnetic storm. As our sun enters a more active part of its solar cycle, we can expect more space weather as the high-energy particles of the solar wind interact with our planet’s magnetic field. The auroras themselves are light released by energetically excited atoms of oxygen and nitrogen high in the upper atmosphere.
Earth is not the only place in the solar system to experience these light shows. With their strong magnetic fields, Jupiter and Saturn have auroras that make Earth’s look paltry in comparison. (Image credit: J. Stevens; via NASA Earth Observatory)
Deciphering Krakatau
In 1883, the eruption of Krakatau (also called Krakatoa) shook the world, sending shock waves and tsunamis ricocheting across the globe. Some of the smaller waves hit shorelines in the Atlantic and Pacific that were entire continents and ocean basins away from the original explosion. At the time, scientists were so perplexed by the phenomenon that they blamed coincidental earthquakes for the wave action.
Only when Tonga experienced a similarly devastating volcanic eruption earlier this year were scientists able to verify what they’d long suspected: these smaller tsunamis were not caused by solid material displacing water; instead they are the result of atmospheric pressure waves coupling to the ocean. Follow the full story over at Quanta. (Image credit: M. Barlow; via Quanta; submitted by Kam-Yung Soh)
Re-Entry For X-Wings
Fans of sci-fi and fantasy have a long-standing tradition of exploring the physics and/or practicality of creations in their fandom, and Star Wars fans are no exception. Here engineers ask whether Luke Skywalker’s X-wing fighter could survive the descent through Dagobah’s atmosphere as he searched for Master Yoda. Their results are based on a numerical simulation, with some assumptions about the spacecraft’s descent path and design as well as the planet’s atmosphere. Fans of the Jedi will be glad to hear that the X-wing can survive its supersonic descent intact, delivering the last Jedi safely to his mentor. (Image credit: Y. Ling et al.)
Ant Bridge
As red ants scout their way to food, the terrain can sometimes get in the way. Here a leading scout has made their body into a bridge that their fellows can use to cross the watery gap. Take a close look at the water’s surface and you’ll see that the meniscus curves up to meet the rocks. That’s a clue that this image is really very small! For water on Earth, that curvature only occurs at lengths below a couple of millimeters, where surface tension has the power to overcome gravity’s efforts to flatten the surface. The ants’ bridge is only possible because the red ant is small enough and light enough for surface tension to support it. Learn more about the amazing interactions of ants and water in some of my previous posts. (Image credit: Chin Leong Teo; via Colossal)
Explaining the Roaming Rocks
For nearly a century, the long meandering tracks etched into Death Valley’s Racetrack Playa remained a mystery. Clearly, some force was pushing the heavy rocks there and leaving behind these grooves. But with the remoteness of the location, it took investigators years to catch the rocks in action and solve the puzzle. For those who haven’t watched the video yet, I’ll refrain from revealing the answer here (though you can find it in previous FYFD entries)! I’ll just say that it requires all the right conditions to come together. (Image and video credit: Physics Girl; for related research see here)
Teaching Diffusion With Eggs
Many cultures around the world marinate hard-boiled eggs — like pickled eggs in Europe or tea- and soy-infused eggs from Asia. These delicacies offer a fun (and tasty) way to demonstrate the concept of diffusion, the tendency of a substance to move from areas of high concentration to low concentration via random molecular motion.
Simply steep peeled, hard-boiled eggs in your sauce (or food dye) of choice. Remove an egg every so often and slice it in half to see how far the sauce traveled. You can also play with the temperature to accelerate the diffusion. The longer an egg steeps and the hotter its surroundings, the further into the egg white the sauce will diffuse! (Image credit: Wordridden; research credit: C. Emeigh et al.)
Fast Fractal Fingers
With the right balance of viscosity and surface tension, many fluid combinations can form fractal or dendritic patterns. Here, researchers use a drop of food coloring atop a mixture of water and xanthan gum. Depending on the concentration of gum (and the age of the viscous fluid) different fractal patterns spread quickly across the surface. (Image and video credit: R. Camassa et al.)
Within the Bubble’s Pop
To our eyes, a soap bubble appears to pop instantly, but when observed in high-speed video, the process is far more complex. In this video, the Slow Mo Guys pop human-sized bubbles, giving us an opportunity to appreciate the rupture process at speeds up to 50,000 frames per second.
Once the rupture starts, the hole spreads very symmetrically. But as the hole grows, the remaining soap film starts distorting. As Gav and Dan observe, the far side of the bubble actually wrinkles up before the rupture front arrives and tears the remaining fluid into droplets! (Image and video credit: The Slow Mo Guys)
