For anyone who has traveled commercially, turbulence is a word that describes the “feeling” of being tossed or shaken around while on an airplane. Many different aspects in the weather world can influence turbulence outside of the obvious thunderstorm type impacts. The two most important terms in the turbulence equation for the generation of turbulence are wind shear and buoyancy (a broad example of buoyancy impacts is above), which are in some way related to all the processes/features that will be discussed below.
This article will focus primarily on low level or boundary layer turbulence. Any sort of frontal feature, whether a cold front, warm front, dry line, etc, tends to generate turbulence via the wind shear present across these boundaries. In addition to the wind shear, buoyancy creating thermals within the boundary layer may be rather robust, depending on which side of the front the aircraft is situated. Across these fronts turbulence may be rather robust and a danger for any aircraft flying, ascending, or descending within the boundary layer.
Sea breezes and land breezes are another boundary similar to an outflow boundary, and to a lesser extent a cold front, that can cause turbulence. The change in wind generates horizontal wind shear and depending on the thermodynamics present during this situation, buoyancy becomes important producing rising thermals and hence, turbulent conditions. Above is an example of a sea breeze on radar in Maryland taken during the evening of May 24th (credit to radarscope).
Mountain waves are another source of turbulence. In the lee of a mountain, with the right conditions such as winds perpendicular to the mountain with air rising over the mountain encountering an inversion will create these oscillatory waves with embedded turbulent circulations known as rotor clouds. These mountain waves are often very turbulent and a hazard for aircraft. Similarly, down sloping wind storms originating from this air rising over the mountain can be very dangerous to aircraft. These conditions can produce winds upwards of 50+ knots in the lee of the mountain (Boulder, CO is famous for their down sloping wind storms). This can create some of the worst turbulence for aircraft. Above is a diagram of mountain waves. *
Being that turbulence is a wind phenomenon, most of the time it is not visible. However, turbulence can physically be represented if there is enough moisture present. The turbulence manifests itself as beautiful wave breaking Kelvin-Helmholtz clouds. An example of such is shown above, credit to Brooks Martner, (the physical manifestation of the wind shear is quite evident as the upper levels of the cloud are moving faster than the lower levels, hence causing “breaking waves”).
Next time you look up in the sky and see resemblances of breaking wave type structures, not only will you have a visually pleasing sight, you will know the environment is becoming increasingly turbulent!
*There is a lot more that goes into mountain waves and down sloping windstorms. Be on the lookout and stay tuned to GWCC for Part 2 and one of my next pieces for an in depth look at down sloping wind storms.
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©2018 Meteorologist Joe DeLizio