FYFD

Tag: turbulence

  • Swirls of Green and Teal

    Swirls of Green and Teal

    Captured in March 2024, this satellite image of the Gulf of Oman comes from an instrument aboard the PACE spacecraft. The picture of a phytoplankton bloom is not quite natural-color, at least not as our eyes would see it. Instead, engineers combined data taken from multiple wavelengths and adjusted it to bring out the fine details. It’s not what we’d see by eye, but every feature you see here is real.

    Traditionally, the only way to identify the species of a phytoplankton bloom like this one is by taking a sample directly. But PACE’s instruments can detect hundreds of wavelengths of light, offering enough color detail that scientists may soon be able to identify and track phytoplankton species by satellite image alone. I wonder if distinguishing species could also provide some quantitative flow visualization from a series of these images. In the meantime, at least we can enjoy the view! (Image credit: J. Knuble; via NASA Earth Observatory)

  • Measuring Microfibers in Turbulence

    Measuring Microfibers in Turbulence

    Microplastic pollution is on the rise, especially in waterways. Microfibers — millimeters in length but only microns in diameter — are especially prevalent, as they get washed out of synthetic clothing. Collecting these pollutants first requires understanding how they move and cluster in turbulent flows. Researchers investigated that using a small water channel and high-resolution cameras.

    The team followed microfiber strands as they moved through turbulence, paying special attention to how the fibers tumbled (rotating about their short axis) and spin (rotating around their long axis). How much fibers tumbled depended on the turbulence level; with more intense turbulence, the fibers tumbled more. Rates of spinning, they found, were consistently even higher than those for tumbling. By better understanding how microfibers behave in turbulence, we’ll be able to, for example, predict how far plastics will travel before settling to the ocean floor. (Image credit: Adobe Stock Photos; research credit: V. Giurgiu et al.; via APS Physics)

  • Measuring Ocean Upwelling

    Measuring Ocean Upwelling

    Large-scale ocean circulation is critical to our planet’s health and climate. In this process, seawater near the poles cools and sinks into the deep ocean, carrying dissolved carbon and nutrients with it. Later, that cold water gets pushed back up to the surface elsewhere, where it warms, and the cycle repeats. Although the theory behind this circulation has been around for decades, it’s been difficult to observe the rise, or upwelling, of water from the depths. But a recent study used a fluorescent, non-toxic dye to measure upwelling directly.

    Researchers deployed 200 liters of dye just above the floor of a marine canyon near Ireland, then monitored the dye’s movement for several days at a depth of 2200. They found that turbulence along the slope of the canyon drove upwelling at speeds of about 100 meters per day, much faster than global rates. The authors suggest that this kind of topographically-enhanced upwelling could be a major factor in setting overall ocean circulation. (Image credit: visualization – NASA, ship – S. Nguyen; research credit: B. Wynne-Cattanach et al.; via Physics World)

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    “Aquakosmos – Ch. 2”

    Colored inks bulge and billow around flowers in filmmaker Christopher Dormoy’s “Aquakosmos – Ch. 2”. Because ink is denser than the surrounding water, it sinks, forming mushroom-like shapes as the Rayleigh-Taylor instability takes over. One of the fun things about this particular video is that we see the Rayleigh-Taylor instability at many different sizes, depending on the size and speed of different falling dyes. (Video and image credit: C. Dormoy)

  • Sediment Swirls

    Sediment Swirls

    Turbulent flows feature swirling eddies over a range of sizes — the larger the size range, the higher the Reynolds number. In this satellite image, sediment highlights these eddies in shades of turquoise, showing off the complexity of the flows created where rivers, ocean, and tides meet. The eddies we see here stretch from kilometers in width down to a handful of meters, but the flow’s turbulence persists down to millimeter-scales before viscosity damps it out. (Image credit: L. Dauphin; via NASA Earth Observatory)

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  • The Real Butterfly Effect

    The Real Butterfly Effect

    The butterfly effect — that the flapping of a butterfly’s wings in Brazil can cause a tornado in Texas — expresses the sensitivity of a chaotic system to initial conditions. In essence, because we can’t possibly track every butterfly in Brazil, we’ll never perfectly predict tornadoes in Texas, even if the equations behind our weather forecast are deterministic.

    But this interpretation doesn’t fully capture the subtleties of the situation. With fluid dynamics, the small scales of a flow — like the turbulence in an individual cloud — are linked to the largest scales in the flow — for example, a hurricane. For short times, we’re actually quite good at predicting those large scales; our weather forecasts can distinguish sunny days and cloudy ones a week out. But at smaller scales, the forecast errors pile up quickly. No one can forecast that an individual cloud will form over your house three days from now. And because the small scales are linked to the larger scales, the uncertainties from the small scale cascade upward, limiting how far into the future we can reliably predict the weather.

    And, unfortunately, drilling down to capture smaller and smaller scales in our models can’t fix the problem, unless our initial uncertainties are identically zero. To get around this problem, weather forecasters instead use ensemble forecasting, where they run many simulations of the weather with slightly different initial conditions. Those differences in initial conditions let the forecasters play with those initial uncertainties — how accurate is the temperature reading from that station? How reliable is the instrument reporting that humidity? How old is the satellite data coming in? Once all the forecasts are run, they can see how many predicted sunny days versus rainy ones, which ones resulted in severe weather, and so on. Often the probabilities we see in our weather app — like 30% chance of rain — depend on factors including how many of the forecasts resulted in rain.

    Unfortunately, this butterfly effect permanently limits just how far into the future we can predict weather — at least until we fully understand the nature of the Navier-Stokes equations. For much more on this interesting aspect of chaos, check out this Physics Today article. (Image credit: NASA; see also T. Palmer at Physics Today)

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  • A Shallow Origin for the Sun’s Magnetic Field

    A Shallow Origin for the Sun’s Magnetic Field

    The Sun‘s complex magnetic field drives its 11-year solar activity cycle in ways we have yet to understand. During active periods, more sunspots appear, along with roiling flows within the Sun that scientists track through helioseismology. Longstanding theories posit that the Sun’s magnetic field has a deep origin, about 210,000 kilometers below the surface. But new measurements have prompted an alternate theory: that the Sun’s magnetic field originates in its outer 5-10% due to a magnetorotational instability.

    Magnetorotational instabilities are usually associated with the accretion disks around black holes and other massive objects. When an electrically-conductive fluid — like the Sun’s plasma — is rotating, even a small deviation in its path can get magnified by a magnetic field. In accretion disks, these little disruptions grow until the disk becomes turbulent.

    By applying this idea to the sun, researchers found they were better able to match measurements of the plasma flows beneath the Sun’s surface. With measurements from future heliophysics missions, they believe they can work out the mechanisms driving sunspot formation, which would help us better predict solar storms that can damage electronics here on Earth. (Image credit: NASA/SDO/AIA/LMSAL; research credit: G. Vasil et al.; via Physics World)

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    Fish Ladders Keep Species Swimming

    Dams often use fish ladders to help migratory species make their way upstream without interruption. In this video, Grady from Practical Engineering discusses some of the considerations that go into this special infrastructure and what kinds of designs work for different species. The first challenge for any dam is attracting fish to the ladder, which is often done by regulating the water flow at the entrance to create the velocity and turbulence that fish look for when going upstream.

    Once fish are in the ladder, they travel up a series of jumps that break the dam’s elevation into manageable steps. Different dams use various baffle designs to create jumps suited to their local species and the way they like to swim. Calmer spots in each section give fish a spot to rest before they carry on. In well-designed systems, the vast majority (97%!) of fish that enter a ladder make it through to the other side. (Video and image credit: Practical Engineering)

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  • Warming Temperatures Increase Turbulence

    Warming Temperatures Increase Turbulence

    After multiple high-profile injuries caused by atmospheric turbulence, you might be wondering whether airplane rides are getting rougher. Unfortunately, the answer is yes, at least for clear-air (i.e., non-storm-related) turbulence in the North Atlantic region. It seems that climate change, as predicted, is increasing the bumpiness of our atmosphere. There are a couple of mechanisms at play here.

    The first is that warming temperatures fuel thunderstorms. When ground-level temperatures and water temperatures are warmer, that provides more warm, moist air rising up and feeding atmospheric convection. Especially in the summertime, that translates into stronger, more frequent thunderstorms; even with flights avoiding the storms themselves, there’s greater turbulence surrounding them.

    The second mechanism relates to wind, specifically in the mid-latitudes. In general, a temperature difference between two regions causes stronger winds. (Think about the windy conditions that accompany an incoming cold front.) At the mid-latitudes, the difference between cold polar regions and warmer equatorial ones creates a strong wind, known as the jet stream. Now, as temperature gradients increase at cruising altitudes, the jet stream gets stronger, which means bigger changes in wind speed with altitude. And its those wind speed differences at different heights that drive turbulence.

    So, yes, we’re likely to see more turbulent flights now and in the future. But, fortunately, there’s a simple way to avoid injuries from that bumpiness: buckle up! If you keep your seat belt fastened while you’re seated, you can avoid getting tossed around by unexpected G-forces. (Image credit: G. Ruballo; see also Gizmodo)

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    The Solar Corona in Stunning Detail

    The ESA’s Solar Orbiter captured this beautifully detailed video of our sun‘s corona last September. The Solar Orbiter took this footage from about 43 million kilometers away, a third of the distance between the sun and the Earth. Scattered across the visible surface are fluffy, lace-like features known as coronal moss. Along the curving horizon, gas spires called spicules stretch up to heights of 10,000 kilometers. The video also highlights a “small” eruption of plasma that is nevertheless larger than the entire Earth. We can even see evidence of coronal rain, denser and darker clumps of plasma that gravity pulls back toward the sun. (Video and image credit: ESA; via Colossal)