MH

In-Depth Notes on Turbulence, Weather Patterns, and Icing

Turbulence in Flight

  • Definition: Irregular motion of an aircraft caused by various factors.

  • Causes:

    • Convective currents (Convective Turbulence)

    • Obstructions in wind flow (Mechanical Turbulence)

    • Wind shear

  • Categories of Turbulence:

    • Light to extreme variations based on intensity.

Types of Turbulence

  1. Convective Turbulence

    • Description: Caused by turbulent vertical motions from convection currents.

    • Explanation:

      • Due to uneven heating of the Earth's surface, causing warm air near the ground to rise and cooler air to descend.

      • Most active on warm afternoons with light winds.

      • Best avoided by flying above clouds.

  2. Mechanical Turbulence

    • Definition: Results from obstructions such as trees, buildings, and mountains disrupting smooth wind flow.

    • Effects: Can create vortices and deviations in airflow, experienced more at lower altitudes.

    • Intensity Factors:

      • Higher wind speeds and rougher surfaces cause greater turbulence.

  3. Wind Shear Turbulence

    • Description: Refers to sudden changes in wind speed/direction over a small area.

    • Relation to Other Factors:

      • Occurs where different wind currents meet.

      • Temperature Inversion: Strong wind shears often occur across inversion layers.

Mountain Weather

  • Mountain Waves:

    • Generated when wind is forced to rise over a mountain, creating oscillations on the downwind side.

  • Conditions:

    • Weak winds or dense air can prevent air movement over peaks.

    • Unstable atmosphere can lead to thunderstorms.

    • Strong, stable winds can generate waves.

  • Ingredients for Mountain Waves to Form:

    1. Strong winds that can get over mountain peaks.

    2. Stable air that resists rising (unlike unstable, convection conditions).

    3. Wind direction must be perpendicular to the mountain range.

Kelvin-Helmholtz Waves

  • Definition: Vertical waves generated by wind shear, producing wave-like clouds under certain moisture conditions.

  • Occurrence: When upper air moves faster than lower air, it results in “rolling” cloud formations, indicating wind shear.

Persistent Horizontal Roll Vortices (Rotors)

  • Trapped Lee Waves:

    • Form when stable air flows over mountains; traps waves close to the surface.

    • Can cause turbulence and cloud formations like lenticular clouds on the mountains' lee side.

    • Rotors: Horizontal vortices beneath mountain wave patterns; indicate extreme turbulence.

Types of Mountain Clouds

  • Cap Clouds: Occur at mountain tops due to orographic lift.

  • Lenticular Clouds: Lens-shaped clouds found in wave crests.

  • Kelvin-Helmholtz Clouds: Indicate wind shear, not necessarily linked to mountains.

  • Rotor Clouds: Chaotic clouds indicating strong turbulence.

Tropical Weather Systems

  • Subtropical High-Pressure Belts:

    • Located around 30° latitude; influences weather patterns.

    • Varies between summer (lows over land) and winter (lows over water).

  • Impacts:

    • Bermuda High affects tropical cyclones and weather in North America.

  • Monsoons: Seasonal wind patterns causing dramatic weather shifts, especially in tropical regions.

Icing in Aviation

  • Types of Icing:

    1. Rime Icing: Rough, opaque ice from supercooled droplets; occurs at colder temperatures.

      • rime icing formation favors colder temperatures, lower liquid content, and smaller droplets.

      • occurs at temperatures colder than -15c

    2. Clear Icing: Glossy ice formed by the slow freezing of large droplets; supercooled water droplets.

      • is more often in an enviornment with warmer temperatures, higher liquid water contents, and larger droplets

      • less than -10c

    3. Mixed Icing: Combination of rime and clear ice due to variations in droplet size and temperature

  • Locations of Icing:

    • Stratiform Clouds: Typically light to moderate icing.

    • Cumuliform Clouds: Severe icing due to updrafts, more likely between 0°C and -20°C.

Icing factorsI

Icing potential is heavily temperature dependent

  1. supercooled liquid water content important in determining how much water is available for icing, highest quantities are found in commuliform clouds and lowest in stratiform clouds.

  2. the outiside air temperature

  3. must be 0C almost all icing tends to occur between 0c and -20c. In altitude terms, the peak of occurence is neat 10,000ft with approximately half of incidents occurring between 5,000 and 13,000ft