Cloud streets: Bering Sea formation from Aqua.

Cloud Streets: Beautiful, Long Cloud Fingers off the Alaska Coast

Cloud Streets: Beautiful, Long Cloud Fingers off the Alaska Coast

Bad Astronomy
The entire universe in blog form
Sept. 15 2015 9:45 AM

Cloud Streets Bering Down

bering_cloudstreets_promo

I love odd and unusual cloud structures, especially when they form interesting patterns. There are lots of different kinds, but when you’re looking down from orbit, I think cloud streets are the coolest.

“Cloud streets?” you ask. “What are those?”

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cloud streets
The sky is paved with cloud streets!

Photo by NASA/Jeff Schmaltz, MODIS Land Rapid Response Team, NASA GSFC

That is the view from NASA’s Aqua satellite, designed to watch our planet’s water. It’s part of the critical (and politically threatened) Earth Observing System, birds that keep track of the Earth’s water, air, land, and climate.

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Phil Plait writes Slate’s Bad Astronomy blog and is an astronomer, public speaker, science evangelizer, and author of Death From the Skies!  

That shot (go grab the much embiggened version, which is astonishing) was taken over the Bering Sea, and is centered about halfway between Russia on the left and Alaska on the right. The little squiggly island just above center is St. Matthew Island, and you can see part of the Aleutian Islands arc to the lower right.

The cloud streets are the long, linear fingers of clouds flowing down and to the left (roughly southwest). I’ve described them before; they form when cold air from over the land blows offshore over warmer water. The air over the water is rising, but the cold air acts like a lid. The warm air hits it, gets spread out to the sides, then starts rotating in long cylinders. Here’s a diagram:

cloud street diagram
Rising air slams into cooler air above it and starts to rotate in oppositely spinning cylinders.

Diagram by Daniel Tyndall, Departmant of Meteorology, University of Utah

Each “street” spins in an opposite direction, and the rotation can be stable for hundreds of kilometers. They occur anywhere cold land blows air onto warm waters, so they appear over Greenland’s coasts, the Great Lakes, and obviously Alaska. I don’t think I’ve ever seen this for myself; my maritime experience hasn’t included steaming off of a wintry location. Although the scale is pretty big, it must be neat to be under these. They probably look like mackerel clouds but on a much larger scale.

I didn’t know these existed until I became a satellite photo nerd just a few years ago. It’s amazing what nature can dream up, and what we can see when we make the effort to look.