Anyone who’s ever been on a plane has experienced that uneasy feeling when the plane begins shaking and the seatbelt sign lights up. For the most part, this experience known as turbulence lasts a few minutes. Then, the airplane stabilizes. There are different kinds of turbulence, such as turbulence caused by storms, winds or mountains. They are easily detected by airlines crossing certain regions. Clear air turbulence, though, are not as easy to find as the other forms. These come without warning and occur at any time during the flight. Although they are hard to detect, pilots and air traffic controllers use certain cues to determining when to expect clear air turbulence.
What is it?
Clear air turbulence usually occurs in boundaries between the jet stream, according to Popular Mechanics. The jet stream is the areal river that flows when arctic air masses meet warm air from the south. Jet streams appear between 6 to 9 miles above the earth’s surfaces, in the upper levels of the earth’s atmosphere. Strong jet streams occur in the winter because Arctic and tropical air masses create a strong surface temperature, producing more incidence of clear air turbulence. During summer months, jet streams are weaker because temperature variations are not as dramatic. Jet stream, though, is only one factor that contributes to clear air turbulence.
Factors
A temperature gradient occurs when temperatures change rapidly near a particular location, specifically the atmosphere from the equator to the poles. When sun rays hit the Earth near the equator, a net heat gain occurs. The temperatures of the air near the equator rises and flows in the upper atmosphere near the poles. Air temperatures then cool when they reach the poles and returns to the Earth’s surface and flows along the Earth’s surface. These rapid shifts create an atmosphere conducive to clear air turbulence.
Wind shear is the difference in relative speed between two air masses that are next to one another. Excessive wind shear produces vortexes, or whirling air masses, that move around and cause unorganized movements. Clear air turbulence occurs because it is hard to determine air density. Temperature and wind velocity decrease with height in the troposphere, the lower layer of atmosphere.
Detection Methods
Airline radars are unable to detect clear air turbulence because this form of turbulence is not associated with cloud movement with unpredictable air movement. Pilots, therefore, must rely on air pressure and the conditions mentioned above. To navigate clear air turbulence, pilots must maintain recommended velocity when experiencing turbulence. If possible, pilots should follow the jet stream. They must also watch their thermometers for sudden temperature changes and determine if those changes are below or above the jet stream.
Sources:
http://www.popularmechanics.com/technology/aviation/safety/4327148
http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/cyc/upa/jet.rxml
http://itg1.meteor.wisc.edu/wxwise/kinematics/jetcore2.html
