In the midst of a cold snap that sent temperatures 20–40°F (11–22°C) below normal across much of the United States, the Moderate Resolution Imaging Spectroradiometer (MODIS) on the Terra satellite captured this image of cloud streets over the Atlantic Ocean on January 7, 2014. Cloud streets—long parallel bands of cumulus clouds—form when cold air blows over warmer waters and a warmer air layer (or temperature inversion) rests over the top of both.
The comparatively warm water gives up heat and moisture to the cold air above, and columns of heated air called thermals naturally rise through the atmosphere. The temperature inversion acts like a lid, so when the rising thermals hit it, they roll over and loop back on themselves, creating parallel cylinders of rotating air. As this happens, the moisture cools and condenses into flat-bottomed, fluffy-topped cumulus clouds that line up parallel to the direction of the prevailing wind. On January 7, the winds were predominantly out of the northwest.
Cloud streets can stretch for hundreds of kilometers if the land or water surface underneath is uniform. Sea surface temperature need to be at least 40°F (22°C) warmer than the air for cloud streets to form.
NASA Earth Observatory image courtesy Jeff Schmaltz LANCE/EOSDIS MODIS Rapid Response Team, GSFC. Caption by Adam Voiland.
Terra - MODIS
Credit: NASA Earth Observatory
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