Turbulence Flashcards
Describe the four main formation mechanisms for turbulence - convection.
- Air heated by conduction will be less dense and will rise
- Produces up currents called thermals or convection currents
- Air cooled will also sink but this is not as strong as updraughts
Describe the four main formation mechanisms for turbulence - mechanical process.
- Caused by physical obstructions to the normal flow of air such as hills, mountains, coasts, trees and buildings
Describe the four main formation mechanisms for turbulence - clear air turbulence (CAT).
- Can be in cloud or in clear air
- CAT occurs around the boundaries of jet-streams because of the large horizontal and vertical wind-shears
- Feels like driving over cobblestones
Describe the four main formation mechanisms for turbulence - wake turbulence.
- Disturbance in the atmosphere behind an aircraft when it is in the air caused by creating lift.
- Spreads out like a boat wake behind the aircraft and sinks with gravity
- Strongest with heavy aircraft in clean configuration and low speed
Describe the effects of atmospheric stability on convective, mechanical and CAT.
- Convective turbulence is stronger when atmosphere is unstable as more air can rise
- Mechanical turbulence is stronger with an unstable atmosphere as larger vertical extent
- CAT is strongest when atmosphere is unstable as more small changes in wind-shear
Describe the effects on surface roughness on convective, mechanical and CAT.
- Convective turbulence is stronger when surface is rough as it heats unevenly creating sporadic thermals
- Mechanical turbulence is stronger with increased roughness
- CAT is strongest when mountains are rough due to mountain waves
Describe the facts of wind speed/direction on convective, mechanical and CAT.
- Convective turbulence is stronger when speed is high.
- Mechanical turbulence is stronger with high wind speed 90 degrees to mountain or object.
- CAT is strongest when wind speed is high as horizontal and vertical wind-shear is increased
Describe the effects of vertical wind-shear on convective, mechanical, and CAT.
- Convective turbulence is weaker with increased vertical wind-shear as it reduces currents and mixes cold air with warm air.
- Mechanical turbulence is stronger with vertical wind-shear as it encourages mountain waves
- CAT is stronger when any wind-shear is increased
Describe the causes and factors involved with the effects of low-level turbulence due to surface friction.
- The rougher the surfaces the greater the surface friction.
- Can reduce speed at surface to almost stationary creating vertical wind-shear with free-flowing air above
- Will cause wind to veer towards the low due to pressure gradient force being stronger than Coriolis
Describe the causes and factors involved with the effects of low-level wind-shear due to thunderstorms.
- Downdrafts during the mature stage create a gust front increasing both horizontal and vertical wind-shear
- Microbursts can create horizontal wind-shear
- Up and down drafts in the mature stage can create horizontal wind-shear
Describe the causes and factors involved with the effects of low-level wind-shear due to temperature inversions.
- Will separate the fast-moving air above from the cold slower moving air below
- At the boundary between these two, turbulence is generated
Describe the causes and factors involved with the effects of low-level wind-shear due to frontal activity.
- Wind direction and temperature change as front passes
- Creates large amounts of wind-shear and turbulence
Describe the causes and factors involved with the effects of low-level win-shear due to wake turbulence from fixed and rotary winged aircraft.
- Rotary wing aircraft create wake from blades spinning
- Large helicopters create similar wakes to commercial jets
- Fixed wing aircraft create a rotational wind-shear that can invert smaller aircraft caught in their wake.
Describe the techniques used to avoid or minimise the effect of low-level wind-shear.
- Use altitude/fly higher to reduce effects
- Fly above turbulent cloud
- Select route on the windward side of mountains or ridges, this increases updrafts increase in lift and less turbulence
- Slow down below VA
- Read the clouds.
Describe, in accordance with the ICAO definitions, the characteristics of light turbulence.
- Turbulence that momentarily causes slight, erratic changes in altitude and/or attitude (pitch, roll, yaw)
- IAS fluctuates 5-15kts
Describe, in accordance with the ICAO definitions, the characteristics of moderate turbulence.
- Changes in altitude and/or attitude occur but the aircraft remains in positive control at all times
- IAS fluctuates 15-25kts.
Describe, in accordance with the ICAO definitions, the characteristics of severe turbulence.
- Causes large, abrupt changes in altitude and/or attitude. Aircraft may be momentarily out of control.
- IAS fluctuates more that 25kts
State the difference between turbulence and up/down drafts.
- Turbulence has bumpy conditions due to unstable air
- Up/down drafts are uniform in directions and can be smooth, however they can make it almost impossible to control the altitude of the aircraft
- The area between up/down drafts like in a Cb will have turbulence due to horizontal wind-shear
