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Space Earth Japan

Japanese Spacecraft Spots Massive Gravity Wave In Venus' Atmosphere (theverge.com) 84

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.
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Japanese Spacecraft Spots Massive Gravity Wave In Venus' Atmosphere

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  • by xyrw ( 609810 ) * on Tuesday January 17, 2017 @03:19AM (#53681267) Homepage

    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.

    • by Anonymous Coward

      Also, gravity wave != wind, it seems.
      But can someone explain the difference? Reading the wikipedia article on "gravity wave", it still sounds like a wind to me.

      • by ASDFnz ( 472824 ) on Tuesday January 17, 2017 @04:24AM (#53681409)

        It is a bit of a picky difference since a gravity wave can be caused by wind.

        It is essentially the same thing as a wave on the sea which is also caused by wind (primarily) but can be caused by other things, for example, an explosion could cause waves in the sea and it could also cause a wave like this in an atmosphere.

        It is the difference between cause and effect.

        The odd thing about these waves (they have been seen before) no wind process (or any other process) that we are familiar with can cause a wave of this magnitude yet here they are.

        • by nadaou ( 535365 ) on Tuesday January 17, 2017 @05:05AM (#53681487) Homepage

          The odd thing about these waves (they have been seen before) no wind process (or any other process) that we are familiar with can cause a wave of this magnitude yet here they are.

          The basic phenomena is equivalent to a hydraulic in a river downstream of a rock. Kayakers have lots of fun playing in them. If the vertical density gradient in the atmosphere is small enough the waves can grow quite large without too much trouble. With a softly defined upper Venetian atmosphere I'd view it more as an internal wave than a surface wave, then it isn't too surprising.

          I am surprised at the apparent lack of Coriolis and no sign of something similar to Hadley cells at latitudes less than 60 degrees, but then again IANAPAP.

      • Also, gravity wave != wind, it seems.
        But can someone explain the difference? Reading the wikipedia article on "gravity wave", it still sounds like a wind to me.

        Wind is driven by pressure delta. I have no idea why they focus on gravity wave unless it involves a massive amount of material in the atmosphere of the mentioned medium area, that gravity has such a powerful visible effect on due to its density, that we have to play with words because the density is so high we have to give it a new term to paint a picture in someone's head of the magnitude of the effect. Sort of like "fucking awesome" -vs- "pretty cool"....? *shrug*

    • It's misleading to say that gravity waves are caused by gravity. Yes, gravity is required for gravity waves, but it's more complex. Gravity waves are named as such because gravity is the force that restores a vertically displaced parcel of air in a statically stable atmosphere to its original position. In reality, the parcel will overshoot its original location and will oscillate, creating a wave.

      If I force a parcel of air upwards, it will expand and cool, though the total energy of the parcel is conserved.

  • by Rei ( 128717 ) on Tuesday January 17, 2017 @04:01AM (#53681345) Homepage

    .... is the size, not the intensity. The air moves only slightly faster or slower than the surrounding atmosphere as one passes through the wave.

    They weren't expected on Venus, though. Venus's surface is dozens of kilometers down, thick and "soupy" there, transitioning to thinner layers above. It was surprising to see that surface features that far away, in a fluid that can compress, would still make clear phenomena like gravity waves in the high atmosphere.

    • by Anonymous Coward

      I'm not very familiar with the structure of the Venusian atmosphere, so maybe there's something I don't understand here. In the Earth's atmosphere, the tropopause acts a bit like a flexible lid. For example, if you have a thunderstorm that ascends to the tropopause, you will get an overshooting top as the updraft parcels are carried past their equilibrium level by the momentum they andcquired in the updraft. They will then oscillate as gravity waves along the thunderstorm anvil, which has been observed in s

      • by Rei ( 128717 ) on Tuesday January 17, 2017 @08:34AM (#53682033) Homepage

        Venus has multiple "tropopauses" and "stratospheres", depending on how you define them. The atmosphere is like a layer cake with multiple convection zones (like Earth's troposphere) separated by areas of dynamic stability (like Earth's stratosphere). And again, ~50-70km is an awfullly long way from the surface, and surface winds are weak. But, there's a lot about Venus that we don't understand.

    • It sounds like a "standing wave" in the winds over the mountains. Which could maintain pressure differences that extend much higher and remain for a time.

      Such waves can even have their own internal circulation, such as a horizontal rolling wind that is like a "tube" downwind from the mountains. I have seen such things near where I live, and I have seen videos available online.

      But when the wind at lower levels changes, the standing wave could dissipate quite quickly.

      Have such waves been seen in earth's upper

  • by r1348 ( 2567295 ) on Tuesday January 17, 2017 @04:57AM (#53681471)

    Just the protomolecule building the Ring...

  • Just watching another news program and sort of disappointed it didn't get any coverage. The last few days had quite a bit of coverage about a new and quite small orbit-capable rocket, though the payload is quite small, on the order of 3 kg. There were several stories before the launch, and then some reports of the failure. (The early reports suggest a telemetry failure?)

  • "Here we report the detection of an interhemispheric bow-shaped structure stretching 10,000km across at the cloud-top level of Venus..."

    from the original article, for those of us that don't know archaic measurements.

  • Next it passes to Earth... then Mars... until it goes all around the solar system and returns back to Mercury.

Were there fewer fools, knaves would starve. - Anonymous

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