NASA Rocket Trails Trace Twisting Waves at the Border of Space

Trimethyl-aluminum gas clouds released by the first of three rockets launched as part of NASA’s “Super Soaker” campaign. The curling waves of the Kelvin-Helmholtz instability – appearing briefly in the center of the image before dissipating – may explain how gases mix in what were previously considered stable layers of the atmosphere. Credit: NASA/Super Soaker/Rafael Mesquita

Glowing vapor clouds released from NASA research rockets launched in Alaska in January 2018 trace curling waves high in Earth’s atmosphere, at the very boundary of space, revealing fluid flow structures known as Kelvin-Helmholtz instability.

From a NASA news release on August 4, 2020:

The “surfer waves” in this image, forming high above the Alaskan sky, illuminate the invisible currents in the upper atmosphere. They were measured by trimethyl-aluminum gas released during a sounding rocket launch from Poker Flat, Alaska, on Jan. 26, 2018. Scientists photograph the gas, which is not harmful to humans [Editor’s note: not harmful at those altitudes and in that application] after it instantaneously ignites when exposed to oxygen. The findings were published in JGR: Space Physics.

Such curling waves are a product of the Kelvin-Helmholtz instability, which occurs when streams of gas or liquid pass by each other at different speeds. As the streams grate against one another, they produce characteristic curls that appear all over in nature, from the ocean’s surface to the swirling dust along Jupiter’s belt.

Kelvin-Helmholtz instability in clouds passing low over the Providence River on May 27, 2020. Credit: Jason Major

Researchers from Clemson University in South Carolina observed the Kelvin-Helmholtz instability shown above some 65 miles above Earth. As the waves dissipated, they created turbulence, mixing the gases above and below them. This turbulent sloshing within an otherwise stable layer of the atmosphere shows one way gases move up and down in our atmosphere. It could explain why molecular nitrogen, which is heavy, is sometimes observed much higher than it should be, while lighter atomic oxygen somehow sinks below.

Understanding how winds move through the atmosphere contributes an extra puzzle piece to the entire atmospheric system – where a slight temperature imbalance at the equator can ultimately lead to huge gusts of wind high above the arctic.

Source: NASA