Nothing quite compares to the beauty of fluid dynamics on astronomical scales. What you see here are raw photographs of recent storms at Saturn’s north pole. The recent change in Saturnian seasons has afforded Cassini a sunlit view of the northern pole, which had previously lain in darkness. A roiling vortex filled with clouds being twisted and sheared was revealed near the center of its famed polar hexagon. (Photo credit: NASA/JPL-Caltech/Space Science Institute; submitted by J. Shoer)
Jupiter is home to one of the most famous storms in the solar system, the Great Red Spot, which Earth observations place at a minimum of 180 (Earth) years in duration. Some evidence suggests that it may have been observed by humans as early as 1665. The magnitude of such a storm is almost unimaginable. At its narrowest point, the storm is still as wide as our entire planet and observations from the Voyager crafts indicate that the storm has 250 mph winds. The scale of mixing and turbulence around the storm, seen in photographs, is stunning and beautiful. (Photo credits: NASA/Voyager 1 and Michael Benson; submitted by oneheadtoanother)
The timelapse animation above shows a swirling vortex above the south pole of Saturn’s moon Titan. It completes a full rotation in about nine hours, significantly quicker than the 16-day rotation of the moon. The vortex appears to demonstrate open cell convection, in which air sinks at the center of the cell and and rises at the edges to form clouds along the cell edges. For the most part the dense haze of Titan’s atmosphere prevents scientists from seeing what goes on beneath the clouds, but Titan is thought to have weather cycles similar to Earth’s, except featuring methane rather than water. (Photo credit: NASA, Cassini; submitted by Adam L)
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The cloud bands of Jupiter stripe the planet with turbulence. Throughout its upper atmosphere, Jupiter shows signs of gravity waves and complicated wave patterns. Near the equator, the cloud bands are driven by planetary winds that reach speeds of 500 kph, whereas near the poles, the clouds show greater evidence of mottling and convection. At present, the reasons for this patterning are undetermined. (Image Credit: NASA; via APOD)
The volcanoes of the South Sandwich Islands, located in the South Atlantic, have a notable effect on cloud formation in this satellite photo. Visokoi Island, on the right, sheds a wake of large vortices that distort the cloud layer above it. On the left, Zavodovski Island’s volcano does the same, with the added effect of low-level volcanic emissions, which include aerosols. These tiny particles provide a nucleus around which water droplets form, causing an marked increase in cloud formation visible in the bright tail streaming off the island. (Photo credit: NASA, via Earth Observatory)
Two interesting sets of clouds are featured in this satellite photo of the Canary Islands and the coast of Africa. In the upper part of the picture, closed cell stratocumulus clouds cover the ocean. As the wind drives these clouds over the islands, their pattern is disturbed by mountains that force the lower layers of air up and around, forming von Karman vortices and wakes that mingle and twist the cloud patterns to the south of the islands. (Photo credit: European Space Agency; via Wired)
When layers of a fluid are moving at different relative velocities, they shear against one another. This shear can trigger the Kelvin-Helmholtz instability, which develops as a waves along the interface. Here Hubble captures Kelvin-Helmholtz waves along the cloud bands of Jupiter, but such clouds are also not uncommon here on Earth. (Photo credit: J. Spencer and NASA)
Last week, Birmingham, Alabama got treated to a special cloudy day, thanks to some Kelvin-Helmholtz waves, shown above. When a layer of faster moving fluid shears a slower moving fluid, this instability can form and cause some spectacular mixing. In this case, the lower, slower fluid was cool and moist enough to contain clouds, enabling us to see the effect with the naked eye. The same mechanism is responsible for the shape of breaking ocean waves and can even be seen in the atmospheres of gas giants like Saturn and Jupiter. (submitted by David B)
Cloud streets–long rows of counter-rotating air parallel to the ground in the planetary boundary layer–are thought to form as a result of cold air blowing over warm waters while caught beneath a warmer layer of air, a temperature inversion. As moisture evaporates from the warmer water, it creates thermal updrafts that rise through the atmosphere until they hit the temperature inversion. With nowhere to go, the warmer air tends to lose its heat to the surroundings and sink back down, creating a roll-like convective cell. (Photo credits: NASA Terra, NASA Aqua, and Tatiana Gerus)
This satellite image shows the cloud wakes of two small, volcanic islands off the coast of Chile. The disruption in airflow caused by the islands results in 100 km long cloud-free V-shaped wakes, even though the islands themselves are barely visible in the image. Such variation in the size of the obstacle compared to its effect is not unusual in fluid mechanics, but the scale, in this case, is impressive. #
