Wednesday, August 23, 2017

Night-time Snow Storms on Mars

Sketch showing the processes of Martian snowfall. Image Credit: Nature Geoscience

Mars has surprisingly powerful snowstorms, which form at night. Although the planet has relatively little water vapor in its atmosphere, clouds of water-ice crystals can still develop. A team led by Aymeric Spiga of the Laboratory of Dynamic Meteorology in Paris used a high-resolution atmospheric model to study how those clouds behave over the Tharsis Montes region of Mars.

After sunset, when the air cools, water-ice clouds radiate away heat — a process that creates strong downward- and upward-flowing winds. This atmospheric churning carries water-ice particles downward, where they precipitate out as snow.

Spacecraft orbiting Mars have detected this night-time atmospheric mixing, and NASA’s Phoenix lander also spotted streaks suspected to be snow on the ground beneath a night-time cloud. The latest work ties those observations together.

Researchers had thought that snow formation on Mars was a slow and gentle process, and will now have to rethink their ideas about the Martian water cycle.

New research about the atmosphere of Mars was published by Nature Geoscience in an article co-authored by SETI Institute scientist, David Hinson. The article, Snow precipitation on Mars driven by cloud-induced night-time convection, is available online. Other co-authors of the article were Aymeric Spiga, Jean-Baptiste Madeleine, Thomas Navarro, Ehouarn Millour, Francois Forget and Franck Montmessin.

David Hinson was responsible for the radio occultation measurements that revealed the presence of unexpected night-time convection, or turbulent mixing, in the lower atmosphere of Mars. Radio occultation uses radio signals for remote sensing of planetary atmospheres and rings.

The research team shows that the convection, which arises from radiative cooling by water-ice clouds, triggers intense descending air currents and localized nocturnal snowstorms. “The high-resolution atmospheric models explain surprising observations from orbit by Mars Global Surveyor and Mars Reconnaissance Orbiter as well as from the surface by the LIDAR instrument on the Phoenix lander,” says Hinson. “The night-time weather is much more intense than had been expected, with implications for our understanding of the annual water cycle.” This sort of night-time weather activity differs from typical weather patterns on Earth.

Credit: nature.comseti.org

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