Seven waterspouts align as lava from the Hawaiian volcano Kilauea pours into the ocean in this striking photo from photographer Bruce Omori. Like many waterspouts–and their landbound cousins dust devils–these vortices are driven by variations in temperature and moisture content. Near the ocean surface, air and water vapor heated by the lava create a warm, moist layer beneath cooler, dry air. As the warm air rises, other air is drawn in by the low pressure left behind. Any residual vorticity in the incoming air gets magnified by conservation of angular momentum, like a spinning ice skater pulling her arms in. This creates the vortices, which are made visible by entrained steam and/or moisture condensing from the rising air. (Photo credit: B. Omori, via HPOTD; submitted by jshoer)

From NSF Science360 Picture Of The Day; July 29, 2015:

Streamwise Vorticity in a Supercell Thunderstorm

This simulation shows a storm that has spawned a tornado. The scene illustrates how a vortex ring forms when a strong updraft punches into the stable stratosphere, causing the surrounding air to curl downward. Such simulations give researchers insights on the conditions that are likely to herald the development of a tornado. The image compares variables from the dataset of the hypothetical thunderstorm. The plot shows vortex lines–the gold streamlines modeled from vorticity–compared to wind velocity as gray streamlines with red representing highest speed values. In a real storm, you can see the clouds billowing upward and corkscrew striations in the rotating cloud, but the relationship between the wind and rotation isn’t exactly clear. Plots like this help to illuminate this relationship, giving a better sense of how the vorticity in the environment is tilted, stretched and intensified in the updraft to make the storm rotate. The image illustrates how vorticity in the environment aligns with the winds feeding into the storm to enhance storm rotation. Improved forecasting and early warning systems have dropped the death toll of tornadoes significantly over the past few decades. But they remain a very real threat to lives and property, especially across the swath of the South-Central U.S. known as “Tornado Alley.” Researchers at the University of Oklahoma and the University of Texas at Austin have developed highly-detailed simulations that reveal the complex inner workings of thunderstorms in order to better predict when tornadoes will emerge.

Visit Website | Image credit: Greg Foss, Texas Advanced Computing Center, University of Texas at Austin

The Curious Motion of Venus

Venus, commonly referred to as Earth’s “evil twin”, has many peculiarities. It serves as an example of an Earth-gone-wrong, with a crushing atmosphere and clouds of sulphuric acid. It has huge vortices swirling at its poles and an average surface temperature of 462°C. However, two of the most curious features are the fact that Venus is almost completely upside down, and is spinning in the opposite direction to most of the other planets in our Solar System.

The axial tilt of a planetary body refers to the angle of a planet’s rotational axis to its orbital axis. The effects of axial tilt result in the changing seasons. For example, Earth has an axial tilt of 23.5°, which is responsible for the difference between our summer and winter. During summer in the northern hemisphere, the North Pole is tilted towards the Sun. This increases the intensity of the Sun’s radiation as well as the length of the day. During winter, the exact opposite occurs as the North Pole tilts away from the Sun.

The Venusian axial tilt is 177.3°, with a net tilt of only 2.7° from the Sun. This means that Venus is almost completely upside down and experiences relatively little change across its seasons. It also has a very slow rotation period which takes 243 Earth days to complete one full spin. Initially, astronomers couldn’t tell how fast Venus spun or the fact that it spun in retrograde (clockwise when viewed from the top). Due to its thick cloudy atmosphere, the Venusian surface wasn’t visible, and without landmarks to use as reference points astronomers weren’t able to measure how fast the planet was spinning on its axis. It wasn’t until the 1960s, when ground-penetrating radars revealed features on the surface of Venus, that astronomers were first able to gauge its rotational speed and direction.

Scientists have put forth numerous theories as to how Venus may have inherited its axial and rotational traits. One possibility involves a huge impact with a proto-planet early in its history, flipping the entire planet and reversing its rotation. Another possibility suggests that tidal locking with the Sun slowed down Venus’ rotation, which was gradually reversed through gravitational interactions with other planets. Further research into our sinister twin could eventually uncover the mystery behind its backwards nature and capsized tilt.

~ eKAT


SOURCES: 1, 2, 3, 4

Reader unquietcode asks:

I saw this post recently and it made me wonder what’s going on. If you look in the upper right of the frame as the camera submerges, you can see a little vortex of water whirring about. Even with the awesome power of the wave rolling forward a little tornado of water seems able to stably form. Any idea what causes this phenomenon?

This awesome clip was taken from John John Florence’s “& Again” surf video. What you’re seeing is the vortex motion of a plunging breaking wave. As ocean waves approach the shore, the water depth decreases, which amplifies the wave’s height. When the wave reaches a critical height, it breaks and begins to lose its energy to turbulence. There are multiple kinds of breaking waves, but plungers are the classic surfer’s wave. These waves become steep enough that the top of the wave  overturns and plunges into the water ahead of the wave. This generates the vortex-like tube you see in the animation. Such waves can produce complicated three-dimensional vortex structures like those seen in this video by Clark Little. Any initial variation in the main vortex gets stretched as the wave rolls on, and this spins up and strengthens the rib vortices seen wrapped around the primary vortex. (Source video: B. Kueny and J. Florence)

A volte può essere utile lasciarsi andare, 
come una persona sul bordo di un ponte, 
che apre le braccia e inizia a volteggiare nel vuoto,
col vento tra i capelli,
l'adrenalina che scorre nelle vene.
Può essere utile per scappare,
e allontanarsi da questa terribile monotonia.
Lasciarsi andare
e farsi trasportare da un vortice
un vortice pieno di emozioni.
Per poi cadere nell'acqua col battito accelerato,
per sentirsi ancora vivi.
—  Nightmareaw

Literature is full of descriptions of monstrous whirlpools like Charybdis, which threatens Homer’s Odysseus. While it’s not unusual to see a small free vortex in bodies of water, most people would chalk boat-swallowing maelstroms up to literary device. But it turns out that, while there may not be permanent Hollywood-style whirlpools, there are several places in the world where the local tides, currents, and topology combine to produce turbulence, dangerously vortical waters, and even standing vortices on a regular basis. 

One example is the Corryvreckan, between the islands of Jura and Scarba off Scotland. In this narrow strait, Atlantic currents are funneled down a deep hole and then thrust upward by a pinnacle of rock that rises some 170 m to only 30 m below the surface. The swift waters and unusual topology produce strong turbulence near the surface and whirlpools pop up throughout the strait. Other “permanent” maelstroms, such as those in Norway and Japan, arise from tidal interactions with similar structures rising from the sea floor.

For more, check out this Smithsonian article, Gjevik et al., Moe et al., and the videos linked above! (Photo credits: Manipula, Tokushima Gov’t, Wikimedia, and W. Baxter; requested by @kb8s)

Vivo nel mare dell'esistenza senza confini
vivo dall'attimo del tuo germoglio saziandomi del tuo essere profondo
vivo immersa nel vortice della tua voce, del tuo volto del tuo esistere
io vivo con te, di te
sognando ogni giorno l'evoluzione della tua mente, del tuo corpo…

R. Calarco

everyonelikespotatissallad asks:

so, how is lift actually generated? i’ve been going through Anderson’s Introduction to Flight (6th Ed.) and while it offers the derivation of various equations very thoroughly, it barely touches on why lift is generated, or how camber contributes to the increase of C(L) 

This is a really good question to ask. There are a lot of different explanations for lift out there (and some of the common ones are incorrect). The main thing to know is that a difference in pressure across the wing–low pressure over the top and higher pressure below–creates the net upward force we call lift. It’s when you ask why there’s a pressure difference across the wing that explanations tend to start diverging. To be clear, aerodynamicists don’t disagree about what produces lift - we just tend to argue about which physical explanation (as opposed to just doing the math) makes the most sense. So here are a couple of options:

Newton’s 3rd Law

Newton’s third law states that for every action there is an equal and opposite reaction. If you look at flow over an airfoil, air approaching the airfoil is angled upward, and the air leaving the aifoil is angled downward. In order to change the direction of the air’s flow, the airfoil must have exerted a downward force on the air. By Newton’s third law, this means the air also exerted an upward force–lift–on the airfoil. 

The downward force a wing exerts on the air becomes especially obvious when you actually watch the air after a plane passes:


This one can be harder to understand. Circulation is a quantity related to vorticity, and it has to do with how the direction of velocity changes around a closed curve. Circulation creates lift (which I discuss in some more detail here.) How does an airfoil create circulation, though? When an airfoil starts at rest, there is no vorticity and no circulation. As you see in the video above, as soon as the airfoil moves, it generates a starting vortex. In order for the total circulation to remain zero, this means that the airfoil must carry with it a second, oppositely rotating vortex. For an airfoil moving right to left, that carried vortex will spin clockwise, imparting a larger velocity to air flowing over the top of the wing and slowing down the air that moves under the wing. From Bernoulli’s principle, we know that faster moving air has a lower pressure, so this explains why the air pressure is lower over the top of the wing.

Asymmetric Flow and Bernoulli’s Principle

There are two basic types of airfoils - symmetric ones (like the one in the first picture above) and asymmetric, or cambered, airfoils (like the one in the image immediately above this). Symmetric airfoils only generate lift when at an angle of attack. Otherwise, the flow around them is symmetric and there’s no pressure difference and no lift. Cambered airfoils, by virtue of their asymmetry, can generate lift at zero angle of attack. Their variations in curvature cause air flowing around them to experience different forces, which in turn causes differing pressures along the top and the bottom of the airfoil surface. A fluid particle that travels over the upper surface encounters a large radius of curvature, which strongly accelerates the fluid and creates fast, low-pressure flow. Air moving across the bottom surface experiences a lesser curvature, does not accelerate as much, and, therefore, remains slower and at a higher pressure compared to the upper surface.

(Image credit: M. Belisle/Wikimedia; National Geographic/BBC2; O. Cleynen/Wikimedia; video credit: J. Capecelatro et al.)


The world’s most powerful artificial tornado is part of the Mercedes-Benz Museum in Stuttgart, Germany. Though popular enough with visitors that the staff will bring out smoke generators to make it visible, the tornado was not built as an attraction - It’s actually part of the building’s fire protection system. The modern open design of the museum meant that conventional smoke removal systems were inadequate. Instead vorticity is generated in the central lobby with 144 wall-mounted jets. The angular velocity created by the jets is strongest at the middle, in the vortex core, due to conservation of angular momentum - exactly the way a spinning ice skater speeds up by pulling his arms in. The core of the vortex is a low pressure area, which draws outside air toward it - this is how the tornado pulls in smoke when there is a fire. The fan on the ceiling provides the pressure draw necessary for the smoke to be pulled up and out of the building at a supposed rate of 4 tons per minute. See the tornado in action here. (Photo credit: Mercedes-Benz Passion; submitted by Ivan)

There’s an infamous supposition about drains swirling one way in the Northern Hemisphere and the other way in the Southern Hemisphere. Destin from Smarter Every Day and Derek from Veritasium have put the claim to the test with experiments on either side of the globe. First, go here and watch their synchronized videos side-by-side. (To synchronize, start the left video and pause it at the sync point. Then start the second video and unpause the first video when the second video hits the sync point.) I’ll wait here.

That was awesome, right?! The demonstration doesn’t work with toilets because they’re driven by the placement of jets around the circumference. And your bathtub doesn’t usually work either because any residual vorticity in the tub gets magnified by conservation of angular momentum as it drains. It’s like a spinning ice skater pulling their arms in; the rotation speeds up. So, to get around that problem, Destin and Derek let their pools sit for a day to damp out any motion before draining. At that point, the Coriolis effect is strong enough to cause the pools to rotate in opposite directions when drained. You may wonder why the effect is so slight for the pools when it’s pretty stark with hurricanes and cyclones. The answer is a matter of scale. The pools are perhaps 2 meters wide, which means that the difference in latitude across the the pool is very slight and therefore, the differential speed imparted by the Earth’s rotation is also very small. Because hurricanes and cyclones are much larger, they experience stronger influence from the Coriolis effect. (Image credits: Smarter Every Day/Veritasium; via It’s Okay To Be Smart)