Shining electric-blue in the night sky, noctilucent clouds (NLCs) look alien. That's because they are. The clouds are seeded by meteor smoke from outer space. Wisps of summertime water vapor rise from the surface of our planet and wrap themselves around the debris of meteors disintegrating in Earth's upper atmosphere, in turn forming icy NLCs. On July 1st and 4th, photographer Adrien Mauduit in Alberta, Canada, captured a remarkable display:
"In this gorgeous 4K video, you can see the different fine structures that appear in NLCs: Waves, billows, knots, bands, and veritable storms revealed themselves in a manner I will never forget!" says Mauduit. "You might think they look like the waves of the ocean or the bottom of a pool; indeed that's exactly what this wondrous natural spectacle looks like."
In fact, they are gravity waves--that is, waves of pressure and temperature rippling away from powerful thunderstorms in Earth's lower atmosphere. Gravity does not vary inside the waves. They get their name from the fact that gravity acts as a restoring force that tries to restore equilibrium to up-and-down moving air. Gravity waves can propagate all the way from Earth's surface up to the mesosphere, where they imprint themselves on the the forms of noctilucent clouds. Mauduit's video of these waves is among the best we've ever seen. He is currently monitoring NLCs from the remote town of High Level, Canada, in support of Project PoSSUM--a NASA-funded citizen science project. Participants receive suborbital astronaut training while they study NLCs from the un-pressurized cabin of a high-flying research aircraft. Mauduit's cameras were on the ground supplementing the ones on the plane.