The Verge: 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. by Andrew Liptak
'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. (This isn’t a gravitational wave, which is a ripple in space-time.) We have these waves in Earth’s atmosphere, too; they interfere with weather and cause turbulence. Scientists have observed atmospheric gravity waves on Venus before: the European Space Agency’s Venus Express spotted several before the end of its mission in 2014. Since its initial observations, Akatsuki has spotted several smaller structures with its infrared cameras in April and May 2016.
'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.'
"Large stationary gravity wave in the atmosphere of Venus" by Tetsuya Fukuhara, et al, here