What is Clear Air Turbulence?
Kelvin-Helmholtz waves
"Clear Air Turbulence (CAT) is the bumpiness experienced by aircraft at high altitudes
(above 18,000 feet) in either cloud-free conditions or in stratiform clouds."
"NOUN : Abbr. CAT Atmospheric turbulence that occurs under tranquil and
cloudless conditions and subjects aircraft to strong updrafts and downdrafts."
What causes Clear Air Turbulence?
CAT is caused by air in the upper atmosphere that becomes unstable and breaks down like waves in the ocean.
These waves are caused by vertical wind shear that causes the air to overcome the stability.
Kelvin-Helmholtz instability.
Where does CAT occur?
Why is CAT a problem?
"In December of 1992, a DC-8 cargo plane westbound out of Denver encountered
severe clear air turbulence. Despite losing an engine (far righthand side) and
6 meters of wing the crew managed to land the plane safely."
CAT is invisible.
Can be hazardous to airplanes.
Turbulence is the leading cause of injuries for airplane pilots and flight attendents.
Each year in the U.S. about 58 passengers are injured by turbulence.
Most of the injured are not wearing seat belts.
How are CAT disasters being avoided?
Deformation-Vertical Shear Index (DVSI) forecasts.
Richardson's Number can predict likelihood mathematically.
LIDAR-Light Detection and Ranging. Detects small particles as the swirl in the air.
Numerous other companies independantly developing detection devices.
In 1995, the FAA announced that seat belts should always be worn to prevent injuries in the case of turbulence.
References
http://orbit-net.nesdis.noaa.gov/arad/fpdt/tifcsts.html
http://www.bartleby.com/61/71/C0397100.html. American Heritage Dictionary of the English Language: Fourth Edition. 2000.
http://www-das.uwyo.edu/~geerts/cwx/notes/chap14/cat.html
http://www.michiganaero.com/lidar.shtml
http://www.scd.ucar.edu/vg/CAT/
http://www.im.aa.com/American?BV_Operation=Dyn_AAPage&referer=index.html&form%25referrer_site=None