For pilots it is important to have a good understanding of turbulence and its causes as it will help him or her to make accurate and timely estimates of possible turbulent conditions. It also helps to have information about the type and favored location of turbulence around your airport and routes you may often fly.
Having a solid background of turbulence types combined with knowledge of local terrain and current weather data will permit the pilot to evaluate possible turbulence on the flight and its effect on the passengers.
To create awareness among pilots and help interpreting observations and forecasts on turbulence phenomena models are used. They act to visualize the characteristics and weather information on turbulence causes. Focusing on critical parameters as tropopause temperatures, windshear (vertical and horizontal), mountain top wind speed and atmospheric stability.
Below a table of the more common types of turbulence we, homebuilt aircraft pilots, normally (except CAT) encounter:
|Low Level (LLT)||Stable or Convective boundary layer||Gust, eddy, thermal, mechanical, dust devil, wake, frontal zone, sheared stable layer, low level jet, shearing gravity waves, land/sea breeze, front, mountain valley breeze, cloud streets|
|Thunderstorm (TNT)||Thunderstorms||Single cell, up & downdraft, multi-cell, super-cell, down/microburst, gust front, tornado, wakes, squall line, mesoscale convective complex|
|Mountain Wave (MWT)||Lee Wave System||Mountain lee waves, rotor, shearing gravity waves, downslope windstorms|
|Clear Air (CAT)||Jet stream cross section||Tropopause and break, jet stream front, sheared stable layers, shearing gravity waves|
To evaluate the turbulence threat we also need some quantitative indicators to diagnose and predict any turbulence intensity. Below a summary:
|Turbulence Type||Intensity Indicator|
|LLT||Surface wind speeds & gusts, low level wind shear, airspeed fluctuations, frontal speed and strength|
|TNT||VIP level, heights of thunderstorms tops, wind shear, tropopause winds, stability index|
|MWT||Mountain top wind speed, tropopause temperature|
|CAT||Maximum wind speed at jet axis, vertical & horizontal wind shear|
Not all of these secondary models are of our of your interest, it just depends on the location where you fly.
When evaluating the terrain you will fly over look for turbulence producing features. Be familiar with general roughness of the area, evaluating the location and absolute and relative heights of terrain features or obstacles that can produce lee waves or eddies. Surface cover as snow, forest, bare soil or water and the orientation of coastlines and hills compared to the general wind flow can help to determine possible sources of thermals and or local disturbances as upslope flows and sea breezes.
The slope and orientation of valleys is very important to identify significant mountain & valley breezes possible interfering with the approach to an airport or runway.
The aviation community has divided turbulence into different categories, although they sometimes overlap:
Occurs within a few thousand feet of the ground where surface features (man made or not) are present. Dry convection, mechanical turbulence caused by buildings, wind shear and turbulence in the vicinity of frontal zones.
Present within and in the vicinity of thunderstorms. Phenomena as wind shear occur near the top and in the wake of a storm, gust front and down burst are usually found at lower levels.
Generated by relatively high terrain featured with lee waves, high and low altitude, sheared layers and rotors.
Free atmospheric turbulence without visible convective activity in the vicinity. Associated with high level frontal zones and Jet stream activity.
Clear air turbulence will not be that common to most low level pilots, unless they fly with airlines a lot.Written by EAI.