vorticity

Il mondo non esiste.
Io non esisto.
Ho gli occhi aperti, ma sogno.
Un vortice di emozioni.
Evado, lontano.
Un istante infinito.
Musica.
Vita.

Quando avevo tredici anni iniziai a leggere Zafòn e me ne innamorai follemente, nel giro di tre anni lessi tutti i suoi libri e mi lasciai trascinare in quel vortice di finzione reale che solo lui era in grado di creare. Fu il primo uomo della mia vita e spesso le sue parole mi tornano alla mente quando ne ho più bisogno. Così stamattina mi sono chiesta quale fosse un ricordo tanto bello della mia vita, mi sono rigirata sul letto per un'ora cercando quello che poteva essere il migliore e poi mi è venuta in mente: ricordiamo solo ciò che non ci è mai accaduto. Questo almeno diceva Zafòn, questo mi sono ripetuta tutto il giorno mentre la mia testa cercava un ricordo felice. Allora eccolo, il mio momento mai vissuto, mia madre incinta di me che passeggia con un vestito nero a fiori, per tanti anni ho avuto questo ricordo che non mi è mai accaduto ma che è reale e nitido. La mia bella mamma con un pancione che sembrava inghiottirla a breve, in un vestito che mi ha detto di avere solo dopo che le raccontai ciò. E oggi ho pensato solo a questo, mi è sembrato un ricordo molto felice e l'ho conservato. Il mio sogno non mi è sembrato più così reale, mia madre ha scansato ogni pensiero con la sua persona, ho sentito calore e ogni incubo se ne è andato.

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)

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)

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

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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)

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

IMAGE CREDIT:
NASA/JPL

SOURCES: 1, 2, 3, 4

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,
fuggire
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