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

Note: Gravity wave != Gravitational wave

[xyrw]

It's worth pointing out that the article talks about a gravity wave, which is a material wave that arises out of a disturbance due to gravity. This should not be confused with gravitational waves, which are ripples in spacetime due to the movement of masses. (The article and summary aren't wrong, but the terminology itself is confusing.)

The effect observed on Venus is in fact quite massive, while gravitational waves are tiny and difficult to observe.

Re: Note: Gravity wave != Gravitational wave

[Anonymous Coward]

I'm the same AC who tried to explain the concept of gravity waves. Parcel theory is a common assumption in meteorology (see http://www.srh.noaa.gov/jetstream/upperair/parcels.html as one of a huge number of examples), even though its conditions are usually violated to some degree in the real atmosphere. Sure, parcel theory isn't perfect, but it does a pretty good job of explaining a lot of things in the atmosphere. It's also extremely common to use it in meteorology to determine things like the amount of instability in the atmosphere or to estimate vertical motions resulting from isentropic upglide and downglide. Anyone who has ever looked at a skew-t diagram from computer model forecast (extremely common in thunderstorm and severe weather forecasting) is applying parcel theory. There area a lot of things we do in meteorology that simplify how the atmosphere works to make forecasting easier. Parcel theory is one of those things, and yet it does a pretty damn good job when we apply it to the real atmosphere.

Yes, the conditions of parcel theory are violated in the real atmosphere. Yes, mixing is one of the ways parcel theory is violated. However, it still works quite well and is extremely common in forecasting. So, although you're technically correct that parcel theory is violated in the real atmosphere, it's usually a close approximation. Entrainment usually isn't significant enough to make a big difference most of the time. That's because usually large volumes of air are displaced, and entrainment generally only occurs around the edges. For example, in a growing cloud, there's entrainment of dry air at the edges, but the interior of the cloud is unlikely to experience much impact from entrainment. The cloud is large enough that the entering is mostly insulated from the effects of entrainment.

As for your cows comment, fuck you.