Turbulence Flashcards
What are the causes of turbulence?
- Convective (or thermal currents)
- Mechanical turbulence
- Wind shear
- Wake turbulence
What is turbulence?
Irregular motion of air from eddies or vertical currents; associated with cumuliform clouds and unstable air
What is convective currents?
Disturbed airflow resulting from air moving vertically in convective currents
What is mechanical turbulence?
Disturbed airflow resulting from air moving past or over obstructions
What is wind shear?
Drastic change in wind speed or direction over relatively short distance
What is wake turbulence?
Turbulent air (lift) behind aircraft that occurs
What is stable air?
Smooth and stable flying conditions since air will resist displacemment
What is unstable air?
Lifted and continues to rise on its own since lifted air is buoyant
What are signs of stable air?
- Stratus-type cloud or fog
- Low visibility when dust, smoke, haze, or fog are present
- Steady precipitation
- Consistent, steady winds
- IFR conditions for ceiling and visibility
What are signs of unstable air?
- Cumuliform clouds
- Good visibility
- Gusty wind
- Showery precipitation
- Thunderstorms
What are the two categories of turbulence?
Friction and Thermal
What is friction turbulence?
Caused by restriction of the movement of the wind
What are the three types of friction turbulence?
- Mechanical turbulence
- Shear turbulence
- Frontal turbulence
What is mechanical tubulence?
Result of friction between air and ground, which causes eddies
What is shear turbulence?
Result of friction between opposing air currents
What is frontal turbulence?
Result of friction between two opposing air masses near frontal surface
What is thermal turbulence?
Caused by rapid change of temperature in atmosphere
What are the two types of turbulence initiated by heat?
- Daytime convection turbulence
- Cold air advection turbulence
What is daytime convection turbulence?
Result of vertical currents caused by unequal heating of Earth’s surface
What is cold air advection turbulence?
When cold air moves over warmer water or land, heating from below creates unstable conditions that favour convection currents and turbulence
What are the intensities of turbulence?
- Light
- Moderate
- Severe
What is macroburst?
Large downburst with horizontal diameter of 4 km or more
What is microburst?
A downburst of less than 4 km in diameter
What is wet microburst?
Occurs when dry air penetrates saturated air leading to rapid evaporation and cooling of the air
What is dry microburst?
Occurs when precipitation evaporates and the air cools and descends
What is virga?
Precipitation falling but not reaching the ground
How many types of wind shear are there and what are they?
- 2 types
- Directional shear
- Speed shear
What is directional shear?
When two winds blowing from different directions meet
What is speed shear?
When two winds are close together and blow from the same direction but at different speeds
What are the two classifications of wind shear?
- High-level wind shear (HLWS)
- Low-level wind shear (LLWS)
What is clear air turbulence (CAT)?
Occurs when fast moving jet stream passes along slow moving one, it disturbs the air and creates turbulence
