Cloud streets are long, parallel bands of cumulus clouds that form when cold air blows over warmer waters. On this day, an outbreak of cool air moved southward across Arctic sea ice toward northern Scandinavia. The difference in temperature between the sea surface and the air in this area can be well over 10 degrees Celsius (18 degrees Fahrenheit).
To transport the heat away from the sea surface, columns of heated air called thermals naturally rise through the atmosphere. The air masses rise until they hit a warmer air layer (temperature inversion), which acts like a lid. The rising thermals then roll over and loop back on themselves, creating parallel cylinders of rotating air. On the upper edge of these cylinders of rising air, clouds form. Along the downward side (descending air), skies are clear.
“The cloud streets are just the manifestation of nature trying to get rid of energy imbalances,” said Erik Kolstad, a weather and climate scientist at the University of Bergen in Norway. “This is also what happens in tropical cyclones, which suck up heat from the warm ocean surface and transport it far away.”