plumes

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Ethereal forms shift and swirl in photographer Thomas Herbich’s series “Smoke”. The cigarette smoke in the images is a buoyant plume. As it rises, the smoke is sheared and shaped by its passage through the ambient air. What begins as a laminar plume is quickly disturbed, rolling up into vortices shaped like the scroll on the end of a violin. The vortices are a precursor to the turbulence that follows, mixing the smoke and ambient air so effectively that the smoke diffuses into invisibility. To see the full series, see Herbich’s website.  (Image credits: T. Herbich; via Colossal; submitted by @jchawner@__pj, and Larry B)

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 Pre-dawn launches provide some of the most dramatic rocket footage. This video is from an October 2nd Atlas V launch, and the really fun stuff starts at about 0:34. As the rocket climbs to higher altitudes, the atmospheric pressure around it decreases. As a result of this low pressure, the rocket’s exhaust gases balloon outward in a giant plume many times larger than the rocket. This happens in every launch, but it’s visible here because the rocket is at such a high altitude that its exhaust is being lit by sunlight while the observers on the ground are still in the dark. The ice crystals in the exhaust–much of the rocket’s exhaust is water vapor–reflect sunlight down to the earth. Around 0:47, a cascade of shock waves ripples through the plume just before the first-stage’s main engine cuts off. Once the engine stops firing, there’s no more exhaust and the plume ends. (Video credit: Tampa Bay Fox 13 News; submitted by Kyle C)

Clean-up of accidents like the 2010 Deepwater Horizon oil spill can be complicated by what goes on beneath the ocean surface. Variations in temperature and salinity in seawater create stratification, stacked layers of water with differing densities. When less dense layers are on top, the fluid is said to be stably stratified. Since oil is less dense than water, one might assume that buoyancy should make an oil plume should rise straight to the ocean surface. But the presence of additives or surfactants in the oil mixture plume can prevent that. With surfactants present, an oil mixture tends to emulsify, breaking into tiny droplets like a well-mixed salad dressing. Even if the density of the emulsion is smaller than the surrounding fluids, such a plume can get trapped at a density boundary, as seen in the photo above. Researchers report a critical escape height, which depending on the plume’s characteristics and stratification boundary, determines whether a plume escapes or becomes trapped.  (Image credit: R. Camassa et al.)

Bubble plumes off Washington, Oregon suggest warmer ocean may be releasing frozen methane

Warming ocean temperatures a third of a mile below the surface, in a dark ocean in areas with little marine life, might attract scant attention. But this is precisely the depth where frozen pockets of methane ‘ice’ transition from a dormant solid to a powerful greenhouse gas.

New University of Washington research suggests that subsurface warming could be causing more methane gas to bubble up off the Washington and Oregon coast.

The study, to appear in the journal Geochemistry, Geophysics, Geosystems, shows that of 168 bubble plumes observed within the past decade, a disproportionate number were seen at a critical depth for the stability of methane hydrates.

H. Paul Johnson, Una K. Miller, Marie S. Salmi, Evan A. Solomon. Analysis of bubble plume distributions to evaluate methane hydrate decomposition on the continental slope. Geochemistry, Geophysics, Geosystems, 2015; DOI: 10.1002/2015GC005955

Sonar image of bubbles rising from the seafloor off the Washington coast. The base of the column is 1/3 of a mile (515 meters) deep and the top of the plume is at 1/10 of a mile (180 meters) depth. Credit: Brendan Philip/University of Washington