Where on Earth: Atmospheric Gravity Waves
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What causes these cloud patterns? This quiz-form segment challenges viewers to identify the cause of parallel bands of clouds visible in a satellite image of the southwestern coast of Africa. It goes on to explain what atmospheric gravity waves are and how they influence cloud formation.
Produced by the Space Telescope Science Institute’s Office of Public Outreach in collaboration with the NASA Earth Observatory (https://earthobservatory.nasa.gov/).
Story adapted from Image of the Day post by Pola Lem: https://earthobservatory.nasa.gov/images/88296/making-waves-in-the-sky-off-of-africa
- Image of Atmospheric Gravity Waves over the South Atlantic Ocean; Terra satellite
- Image of wind waves on ocean; NOAA
- Image of duck wake by Andy Beecroft
- Image of raindrop ripples by Arbyreed
- Movie showing wave propagation; STScI/NASA
- Written by Leah Ramsey
- Designed by Dani Player
- Music from Yesh Music (ASCAP)
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[GENTLE MUSIC]
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Various landscapes. Text, Where On Earth?
This satellite image shows arcs of clouds off the coast of Angola and Namibia.
What causes these cloud patterns? A. Jet trails, B. Brush fires, C. Dust storms, D. Gravity waves
Highlight on D, Gravity waves
Atmospheric Gravity Waves over the South Atlantic Ocean. Many of the waves we are familiar with on Earth are gravity waves. Gravity waves can form when water is pushed upward by a force - like wind, a swimming duck, or the impact of a raindrop – and then pulled back down by Earth's gravity.
Gravity waves also form when air is forced upward – for example by a storm system, a cold front, or a mountain – and then pull back down by gravity.
These clouds mark gravity waves that form when cool, dry air from the Namib Desert flows under warmer, wetter Atlantic Ocean Air, pushing it upward.
The humid ocean air cools as it rises, causing water vapor within it to condense and form clouds.
Gravity then pulls the air back downward, causing the clouds to warm up and evaporate.
The entire column of air oscillates up and down, and the wave propagates outward over the ocean.
The result is a ripple pattern with cloud-covered wave crests and clear wave troughs.
Although they are not always visible, gravity waves are ubiquitous throughout Earth's atmosphere.
From Africa to the Earth as a whole. Text, Music courtesy of Yesh Music (ASCAP)
Various landscapes. Where On Earth?