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Cloud streets: What are they? How do they form?

Orbital view of Great Lakes with clouds in thin parallel lines; entire region snow-covered.
Here, these cloud streets appeared over the Great Lakes on January 20, 2022. Image via MODIS Land Rapid Response Team/ NASA/ GSFC.

What are cloud streets?

Cloud streets are long rows of cumulus clouds that are oriented parallel to the direction of the wind. Their technical name, more specifically, is horizontal convective rolls. As a matter of fact, you’ve probably seen them in satellite photos. Typically, they most often form straight rows, but when the wind driving the clouds hits an obstacle, the clouds might curl into patterns and become von Kármán vortex streets.

How do cloud streets form?

Convection rolls of rising warm air and sinking cool air form cloud streets. First, rising warm air cools gradually as it ascends into the atmosphere. Then, when moisture in the warm air mass cools and condenses, it forms clouds. Meanwhile, sinking cool air on either side of the cloud formation zone creates a cloud-free area. Later, when several of these alternating rising and sinking air masses align with the wind, cloud streets develop.

Diagram of counter-rotating winds indicated by circular arrows.
This diagram depicts convection rolls and the formation of cloud streets. Image via NOAA.

Generally, cloud streets typically form fairly straight lines over large, flat areas such as the ocean. However, when geological features like islands disrupt the flow of the wind, this disruption can create spiral patterns in the cloud streets. This is similar to the way in which large boulders create downstream eddies in rivers. Notably, the spiral patterns in clouds, called von Kármán vortex streets, were named after Theodore von Kármán, a co-founder of NASA’s Jet Propulsion Laboratory. He was one of the first scientists to describe this type of atmospheric phenomenon.

Meteorological phenomena such as cloud streets and von Kármán vortices are a manifestation of Earth’s atmosphere in motion.

The view from above

NASA has taken some amazing photographs of cloud streets over the past few years with the MODIS (Moderate Resolution Imaging Spectroradiometer) instruments on board the Terra and Aqua satellites. As an illustration, the satellite images on this page are from these instruments.

Parallel lines of clouds with a small circular formation and chain of vortices extending from it.
The MODIS instrument on NASA’s Aqua satellite acquired this image of a von Kármán vortex street that formed off the coast of Greenland on February 24, 2009. Image via NASA/ Jeff Schmaltz/ MODIS Rapid Response Team. Read more about this image.
Many curved parallel lines of clouds seen from orbit in black and white.
The MODIS instrument on NASA’s Aqua satellite captured this image of cloud streets over the Black Sea on January 8, 2015. Image via NASA Earth Observatory/ Jeff Schmaltz. Read more about this image.
Cloud streets: Thin parallel lines of clouds extending from ice shelf in black-and-white orbital photo.
The MODIS instrument on NASA’s Terra satellite captured these cloud streets over the Bering Sea on January 20, 2006. Image via Jesse Allen/ NASA. Read more about this image.
Rows of puffy cumulus clouds seen from above with part of airplane wing visible.
View larger. | Typically, cloud streets are most readily seen in satellite photography, but this aerial image comes from Rosimar Rios Berrios, via NOAA/ Hurricane Research Division.

Bottom line: Cloud streets are an atmospheric phenomenon consisting of long rows of cumulus clouds oriented parallel to the direction of the wind.

April 7, 2022

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