File:Cloud Streets over Foxe Basin (MODIS 2021-11-04).jpg

English: Frigid air and strong wind over Nunavut, Canada drew stunning patterns in the clouds over Foxe Basin in early November 2021. The Moderate Resolution Imaging Spectroradiometer (MODIS) on board NASA’s Aqua satellite acquired this true-color image on November 2.

Foxe Basin sits north of Hudson Bay along the Northwest Passages. Approximately 310 mi (500 km) across at its maximum width, the shallow Foxe Basin is one of the richest and most biologically diverse areas of the Canadian Arctic, supporting such species as Sabine’s Gull, bearded seal, walrus, and a summering area for a variety of whales, despite being covered with snow and ice most of the year.

In early November, warm summer temperatures had emptied the waters of Foxe Basin of most of their ice cover, but autumn set the stage for falling temperatures. By November 3, temperatures hovered around -9˚C (15.8˚F) during the daytime as light snow fell over most of the region. Air temperatures over the waters of the Northwest Passages remained relatively warm and moist compared to land. As a steady wind pushed frigid, dryer air from above the land across the water, the stage was set for a spectacular show in the clouds.

As the cold air mass moved over the relatively warm water, it quickly gained warmth and moisture necessary to form clouds. But these are not your typical cumulus clouds. Notice how they line up in organized rows parallel to the direction of the wind. These “cloud streets” are the result of nature trying to balance differences in energy.

Cloud streets occur when columns of heated air—thermals—rise through the atmosphere and carry heat away from the sea surface. The moist air rises until it hits a warmer air layer (a temperature inversion) that acts like a lid. The inversion causes the rising thermals to roll over on themselves, forming parallel cylinders of rotating air. On the upward side of the cylinders (rising air), water vapor condenses and forms clouds. Along the downward side (descending air), skies remain clear.

Cloud streets align along the path of the prevailing wind and usually start slightly offshore. This is because the cold air mass needs some time and distance moving over the water to pick up enough moisture for cloud formation. As the air moves over islands, turbulence occurs, and clouds take on a more rippled appearance. Where there is little wind, the clouds take the form typical of a layer of marine stratocumulus clouds.