Rainbow Bands of Airglow in Gravity Waves above Pico Island
April 14, 2016
During a climb to Pico Mountain, the highest mountain of Portugal (7,713 ft or 2351 m), on Pico Island of the Azores Islands, I stopped to take in the view and photograph a portion of the Milky Way. Note the strange rainbow bands of airglow above the low clouds. Though airglow can be observed telescopically on many nights it's usually hard to detect but on occasion, an approaching storm may initiate noticeable rippling or waves in the upper atmosphere that enhances the airglow. These wavy bands are actually huge parallel structures in the thermosphere, some 56 mi (90 km) overhead, known as gravity waves (not to be with confused with Einstein's gravitational waves). Perspective makes them appear to converge toward the horizon. Gravity waves are thought to propagate upwards from tropospheric disturbances (storms). The bright spot at top left is the Andromeda Galaxy; the glow at the bottom is city lights from the island of Faial.