Tag Archives: Phenomena

What is clear air turbulence?

Clear-air turbulence, abbreviated “CAT,” occurs high in the atmosphere at the cruising altitude of passenger jets. CAT happens in clear sky conditions and where the wind direction and speed changes quickly with height. If you flew on a plane that experiences a jarring bumpiness and yet there are blue skies out the window, then you’ve experienced CAT. It is most common over mountains, near fronts and around the jet stream. It is also more common in winter than summer. Continue reading

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Does sound travel better in fog?

No. Sound is a sequence of pressure waves that propagate through a compressible medium, such as air or water. Sound has to move molecules in order to travel. Sound is transmitted from a source to the surrounding molecules, which vibrate or collide and pass the sound energy along until it eventually reaches our ears. The closer the molecules are to each other, the farther the sound can travel. This is why sound travels farther through water than it does through air and why it is impossible for sound to move through space. Continue reading

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What are those rolls of snow in a farm field?

Those cylinder-shaped masses of rolled-up snow are called “snow rollers.” Some appeared after the pre-Christmas storm, but they are uncommon in the Midwest. (The last time someone told us they saw snow rollers was in February 2003.) While they may look like someone was rolling snow to make a snowman, you won’t see any footprints in the snow as these rolls form naturally. Continue reading

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What was the ring around the moon last month?

As the remnants of Superstorm Sandy approached us on Oct. 29, people in Wisconsin observed a halo on two consecutive nights. These halos resulted from the ice clouds generated from the storm.

A halo is a whitish ring that encircles but does not touch the sun or moon. It is an optical phenomenon that owes its existence to the bending of light by ice crystals, much like the “rainbow crystals” you may hang in your windows. Continue reading

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What are sundogs?

On a day with high ice clouds, you are likely to see shiny, colored regions at either side of the sun. These are sundogs, an optical effect caused by refraction and dispersion of the Sun’s light through ice crystals. When the light rays strike the boundary between the air and water, like an ice crystal, several things can happen. Some rays are turned back in the direction from which they came, the familiar process of reflection. Other rays are transmitted into the crystal. Some of the transmitted rays change direction, a process known as refraction. Continue reading

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