Back on December 16th, residents of Birmingham, Alabama got a strange weather surprise. Now, the people of Birmingham are accustomed to all kinds of bad weather, but wave clouds are somewhat of a foreign thing there.
Wave clouds, or Kelvin-Helmholtz waves as they are scientifically called, are not a rare weather phenomenon in general, they just don't usually occur in Alabama too often. Generally these wave clouds occur in areas of the atmosphere (at cloud level) where winds can build up significant speed. This is the same concept that causes waves to form in the ocean, as thicker fluids are pulled by less-dense, fast-moving air. In Birmingham's case, Chis Walcek, a meteorologist at the Atmospheric Science Research Center at SUNY explained, "In the picture of the Birmingham sky, there is probably a cold layer of air near the ground where the wind speed is probably low. That is why there is a cloud or fog in that layer. Over this cloudy, cold, slow-moving layer is probably a warmer and faster-moving layer of air."
Not to be confused with gravity wave clouds. These are nothing more than waves moving through stable layers in the atmosphere. Typically, these are caused by thunderstorm updrafts as they are trying to punch through the tropopause (this is a very stable layer of air in the atmosphere). The stable air combined with the vertical movement of a thunderstorm updraft tends to generate gravity waves within the clouds that are trying to push into the tropopause. Click on the image below to watch a video of gravity waves.
Sources: NASA, Huffington Post, LiveScience, The Weather Prediction, ABC 33/40, SyFy Dvice
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