Japanese Spacecraft Spots Massive Gravity Wave In Venus' Atmosphere (theverge.com)

An anonymous reader quotes a report from The Verge: The Japanese probe Akatsuki has observed a massive gravity wave in the atmosphere of Venus. This is not the first time such a wave was observed on the Solar System's second planet, but it is the largest ever recorded, stretching just over 6,000 miles from end to end. Its features also suggest that the dynamics of Venus' atmosphere are more complex than previously thought. An atmospheric gravity wave is a ripple in the density of a planet's atmosphere, according to the European Space Agency. Akatsuki spotted this particular gravity wave, described in a paper published today in Nature Geoscience, when the probe arrived at the planet on December 7th, 2015. The spacecraft then lost sight of it on December 12th, 2015, because of a change in Akatsuki's orbit. When the probe returned to a position to observe the bow-shaped structure on January 15th, 2016, the bright wave had vanished. What sets the huge December wave apart from previously discovered ones is that it appeared to be stationary above a mountainous region on the planet's surface, despite the background atmospheric winds. The study's authors believe that the bright structure is the result of a gravity wave that was formed in the lower atmosphere as it flowed over the planet's mountainous terrain. It's not clear how the wave exactly propagates to the planet's upper atmosphere, where clouds rotate faster than the planets itself -- four days instead of the 243 days it takes Venus to rotate once.

Comments

Re: Note: Gravity wave != Gravitational wave

[Anonymous Coward]

Gravity waves depend on the stability of the fluid (in this case, the atmosphere). If the fluid is unstable, the displaced air will accelerate away from its original location. It's the difference between a wave (stable) and a parcel (unstable). In meteorology, we usually discuss stability in terms of parcels because, although imperfect, the assumptions of parcel theory are close enough to be useful in explaining a lot of processes in the atmosphere.

For those who are genuinely interested, here are a couple of links that explain gravity waves:
http://www.theweatherprediction.com/habyhints/64/
http://www.physics.uwo.ca/~whocking/p103/grav_wav.html

Both links, of course, use parcels to help explain gravity waves. The second link is more detailed and introduces the related concept of the Brunt-Vaisala frequency (the period of a gravity wave oscillation; it is infinite or NaN for neutral stability and not purely real for unstable conditions), which is useful in meteorology.

Would you like to contribute to the discussion, or are you just here to troll me, as your most recent post implies?