Last week, the Japanese meteorological satellite Himawari-8 snapped a pretty cool image of Australia from space. The image shows an enormous gravity wave sweeping through the atmosphere off the northern coast of Western Australia.
Gravity waves are not to be confused with gravitational waves. The latter are formed by the literal rattle of space-time and you need huge detectors to measure them. Gravity waves, on the other hand, can be seen very easily. The waves in the ocean are examples of gravity waves.
Gravity waves form at the interface between two fluids, for example, air and sea, but also between two regions of the atmosphere with different properties. In the case of these particular waves, a cold front likely from thunderstorms is to blame – as the air flowed out, it produced oscillations in the atmosphere. The storms moving inland produced waves that were directed back into the sea and with them, they even carried plumes of dust from coastal regions.
Gravity waves in the atmosphere are invisible to our eyes but we can see them with satellites using several approaches. The waves become pretty visible when we are tracking water vapor and in the case of these particular gravity waves, we can follow their progress thanks to thin clouds trapped within their peaks or valleys.
A longer animation produced by Andrew Miskelly from Weatherzone shows the gravity waves form, expand, and eventually disperse over the course of October 20-22. There were several releases of gravity waves during these two days and nights, taking different directions once they were above open water.
The Himawari-8 satellite is in geostationary orbit at a longitude of 140.7° and every 10 minutes it snaps a full-disk image of the Earth, capturing Hawaii all the way across to Yemen. It is designed to provide weather data to Japan, of course, but plenty of countries are visible when you’re looking at Earth from 36,000 kilometers (22,300 miles) away.
Gravity waves in the atmosphere are a common phenomenon. NASA released a beautiful image of waves forming around an island two years ago, for example. They are also not exclusively an Earthly phenomenon. They have been seen in the tenuous envelope of Pluto and the dense atmosphere of Venus.