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Questions and Answers
What causes visible moisture in the atmosphere?
What causes visible moisture in the atmosphere?
Which condition is most favorable for the formation of fog?
Which condition is most favorable for the formation of fog?
Which type of low cloud is known for producing widespread areas of rain?
Which type of low cloud is known for producing widespread areas of rain?
What type of fog forms when warm, moist air moves over a cooler surface?
What type of fog forms when warm, moist air moves over a cooler surface?
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Which type of middle cloud is characterized by a flat, dense, and uniform color?
Which type of middle cloud is characterized by a flat, dense, and uniform color?
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What is a characteristic appearance of altocumulus clouds?
What is a characteristic appearance of altocumulus clouds?
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Which type of cloud is typically associated with thunderstorms?
Which type of cloud is typically associated with thunderstorms?
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What condition must be met for precipitation to occur?
What condition must be met for precipitation to occur?
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Which type of precipitation is characterized by very light and fine drops?
Which type of precipitation is characterized by very light and fine drops?
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What impact does precipitation have on aviation?
What impact does precipitation have on aviation?
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What is meant by atmospheric stability?
What is meant by atmospheric stability?
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What occurs during adiabatic warming of air?
What occurs during adiabatic warming of air?
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What is the average lapse rate?
What is the average lapse rate?
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How does moisture affect air density?
How does moisture affect air density?
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What characterizes a temperature inversion?
What characterizes a temperature inversion?
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Which scenario likely leads to poor visibility?
Which scenario likely leads to poor visibility?
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Which lapse rate is associated with moist air?
Which lapse rate is associated with moist air?
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What happens to air at the dew point?
What happens to air at the dew point?
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What is the phenomenon where surface temperatures drop due to terrestrial radiation on a clear night?
What is the phenomenon where surface temperatures drop due to terrestrial radiation on a clear night?
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What effect does frost have on an airplane's wings?
What effect does frost have on an airplane's wings?
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What is the primary layer of the atmosphere where most weather occurs?
What is the primary layer of the atmosphere where most weather occurs?
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Which gas constitutes the largest percentage of the atmosphere?
Which gas constitutes the largest percentage of the atmosphere?
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What phenomenon causes air to flow towards areas of low pressure?
What phenomenon causes air to flow towards areas of low pressure?
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In which direction does air deflect in the northern hemisphere due to the Coriolis Force?
In which direction does air deflect in the northern hemisphere due to the Coriolis Force?
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Which type of breeze occurs during the day due to land heating?
Which type of breeze occurs during the day due to land heating?
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What is indicated by closely spaced isobars on a weather map?
What is indicated by closely spaced isobars on a weather map?
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What is the highest layer of the atmosphere mentioned?
What is the highest layer of the atmosphere mentioned?
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What causes the formation of local wind patterns?
What causes the formation of local wind patterns?
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What describes the movement of cold air through gaps in mountains due to pressure differences?
What describes the movement of cold air through gaps in mountains due to pressure differences?
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How does warm air behave in the context of convection?
How does warm air behave in the context of convection?
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What happens to the Coriolis force as air moves closer to the surface of the Earth?
What happens to the Coriolis force as air moves closer to the surface of the Earth?
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Which local wind is typically weaker at night due to reduced temperature contrasts?
Which local wind is typically weaker at night due to reduced temperature contrasts?
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What type of air mass is produced by the warming effect as air descends mountains?
What type of air mass is produced by the warming effect as air descends mountains?
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Study Notes
Aviation Weather Meteorology for Pilots
- This is a study guide for aviation weather meteorology, specifically for pilots.
- Chapter 6, Section A covers basic weather theory.
The Atmosphere
- A mixture of gases surrounds the Earth.
- The proportions of gases are fairly uniform up to approximately 260,000 feet.
- The atmosphere is divided into layers defined by various criteria.
Atmospheric Layers
- Troposphere
- Tropopause
- Stratosphere
- Mesosphere
- Thermosphere
Troposphere
- Extends from the surface to approximately 36,000 feet.
- Higher in summer than winter.
- Higher at the equator than the poles.
- Where most weather phenomena occur.
Tropopause
- The top of the troposphere.
- Contains the jet stream, turbulence, and the top of thunderstorms.
Stratosphere
- Extends to approximately 160,000 feet.
Mesosphere and Thermosphere
- Layers above the stratosphere.
Composition of the Atmosphere
- Gases
- Nitrogen (78%)
- Oxygen (21%)
- Other gases (1%)
- Water vapor (0% to 4%)
- Pollutants
Atmospheric Circulation
- Air movement is caused by Earth's gravity and rotation.
- Unequal temperatures on Earth's surface disrupt the equilibrium.
Circulation - Theory
- Temperature varies with sun exposure, length of time, and angle.
- Air compensates for unequal heating through convection.
- Warmer air rises at the equator.
- Cooler air sinks at the poles.
Circulation - Reality
- Three-cell pattern:
- Hadley Cell
- Ferrell Cell
- Polar Cell
Atmospheric Pressure
- Unequal heating causes changes in air density and circulation.
- Altimeter settings vary based on location.
On the Weather Maps
- Isobars connect points of equal pressure.
- Pressure gradient represents the change in pressure over distance.
- Close isobars imply a strong gradient (strong winds)
- Wide isobars imply a weak gradient (lighter winds)
Isobars Identify Pressure Systems
- High-pressure systems
- Low-pressure systems
- Ridges
- Troughs
- Cols
Air Flow
- Air moves from high-pressure areas to low-pressure areas.
- Pressure gradient force determines wind strength (strong isobars = strong winds).
Coriolis Force
- Earth's rotation deflects the path of air.
- Rightward deflection in the northern hemisphere
- Leftward deflection in the southern hemisphere
- No deflection at the equator.
- Greater speed = greater deflection
- Air moves parallel to isobars as Coriolis and pressure gradient forces equal out.
Frictional Force
- Friction slows air near the Earth's surface
- Reduces Coriolis Effect
- Pressure gradient force is stronger, driving air towards low pressure
Global Wind Patterns
- Describes global wind patterns, including prevailing westerlies, trade winds, and polar easterlies
Local Wind Patterns
- Local terrain and water bodies influence wind patterns
- Warmer air rises and cooler air replaces it.
- Same basic principles apply as global circulation.
Sea Breeze
- Daytime heating of land.
- Causes air to rise, and cooler air flows in to take its place.
- Return flow above the sea breeze.
- Winds at 10 to 20 knots to a height of 1,500 to 3,000 feet AGL.
Land Breeze
- Land cools faster than water at night.
- Reverse of daytime sea breeze.
- Smaller temperature contrasts produce less intense winds compared to sea breezes.
- Winds at 1,000 to 2,000 feet AGL.
Valley Breeze
- Mountain slopes heat adjacent air.
- Warmed air flows up the valley.
- Winds at 5 to 20 knots.
- Greater winds several hundred feet above the surface
Mountain Breeze
- Terrain cools at night.
- Cooler air flows down the slopes and valley.
- Winds at 5 to 15 knots.
- Higher winds (up to 25 knots) are possible
Katabatic Wind
- Downslope winds.
- Stronger than mountain breezes.
- Potential for warm or cold winds.
Cold Downslope Winds
- Develop over icy or snowy terrains.
- Develop shallow high-pressure domes, pushing cold air through mountain passes
- High speeds are possible in narrow canyons and valleys
- Known by local names in various regions
Warm Downslope Winds
- Warm air masses move over mountains.
- Develop low-pressure troughs on the lee side of mountains.
- As the air descends, it compresses and warms.
- Rapid temperature increases are possible (up to 20° in an hour)
Atmospheric Stability
- Stability: resistance to vertical motion.
- Stable atmosphere = smooth air; unstable = turbulent, rising air, significant cloud development, and hazardous weather.
Adiabatic Heating/Cooling
- Air expands when rising, cooling adiabatically.
- Air compresses when sinking, heating adiabatically.
Lapse Rate
- The rate of temperature decrease with increasing altitude.
- Average is 2°C (3.5°F) per 1,000 feet.
Water Vapor and Lapse Rate
- Water vapor is lighter than dry air.
- Moist air cools at a slower rate than dry air.
- Dry adiabatic lapse rate is 3°C/1000 feet
Temperature and Moisture
- Combined factors determine atmospheric stability. -Warm moist air = highly unstable -Cold dry air = highly stable
Temperature Inversions
- Temperature usually decreases with altitude.
- Inversion occurs when temperature increases with altitude.
- Typically shallow layers near the surface or at higher altitudes
- Aids in trapping weather/pollutants
Frontal Inversions
- Cold fronts: cool air forced under warm air.
- Warm fronts: warm air rising over cold air
Moisture
- Significant impacts on flight hazards. -High moisture = greater weather problems. -Low moisture = good weather
State of Moisture
- Solid, Liquid, Gas
- Evaporation
- Condensation
- Sublimation
- Deposition
- Melting
- Freezing
Latent Heat
- Heat absorbed or released during phase changes.
- Example – 32°F water to 32° F ice
Humidity
- Moisture in the air.
- Relative humidity compared to total possible.
Dewpoint
- Temperature air must cool to become saturated.
- Used to estimate cloud base levels.
Dew and Frost
- Surface cools below surrounding air dewpoint. -Dew: above freezing, water vapor condenses -Frost: below freezing, water vapor sublimates to ice
Frost and Airplanes
- Frost spoils airfoil surface, reducing lift and increasing drag.
Clouds
- Air cools to the saturation point
- Condensation and sublimation form visible moisture
- Clouds and fog (clouds near the surface)
Cooling of Air
- Lifting
- Moving over a cooler surface
- radiation cooling
Clouds and Fog
- Spread conditions determined by temperature and dewpoint. -Less than 4 degrees F = favorable fog/cloud conditions
Types of Clouds
- Grouped by altitude. - Low, middle, high
- Clouds with vertical development
Low Clouds
- Surface to about 6,500 feet.
- Stratus: layered, stable, uniform
- Nimbostratus: rain-producing, widespread
- Stratocumulus: white, puffy
Fog
- Low cloud with base close to the ground.
- Radiation fog: clear, calm, humid nights
- Advection fog: warm, moist air moves over a cool surface
- Upslope fog: moist, stable air forced up sloping terrain
- Steam fog: cold, dry air moves over warmer water
Middle Clouds
- 6,500 to 20,000 feet AGL. - Altostratus: flat, dense, uniform color, moderate icing possible - Altocumulus: patchy, uniform appearance, frequent from altostratus breaking up, mild turbulence.
High Clouds
- Above 20,000 feet AGL.
- Cirrus: wispy, stable air
- Cirrostratus: thin, white, long bands or sheets
- Cirrocumulus: white, patchy, like cotton, mild turbulence
Clouds with Vertical Development
- Cumulus: fair weather, little icing, mild turbulence.
- Towering cumulus: unstable air, heavy turbulence, icing, pre-thunderstorms.
- Cumulonimbus: thunderstorms, heavy turbulence, icing, hail
Precipitation
- Water in liquid or solid form from the atmosphere to the ground.
- Aviation problems: impacts on visibility, engine performance, braking, and wind
- Precipitation causes: saturation, condensation and freezing
Precipitation Causes
- Condensation/deposition
- Coalescence
- Slow and inefficient
Precipitation Causes continued
- Super-cooled water droplets and water vapor lead to rapid ice crystal growth
Types of Precipitation
- Drizzle
- Rain
- Virga
- Freezing drizzle
- Freezing rain
- Ice pellets
- Hail
- Snow
- Snow grains
- Fallstreaks (mare's tails)
Airmasses
- Large bodies of air
- Uniform temperature and moisture
- Covers hundreds of miles
Source Regions
- Polar
- Tropical
- Continental
- Maritime
Stable Air Characteristics
- Smooth
- Layered clouds
- Restricted visibility
Unstable Air Characteristics
- Cumuliform clouds
- Showers
- Turbulence
Modification of Air Masses
- Airmasses adopt characteristics of the region they move over.
- The degree of change depends on speed, nature of the region, temperature differences, and depth of the airmass.
Warming from Below
- Causes vertical air movement.
- Causes instability.
- Lake effect.
Cooling from Below
- Vertical movement inhibited.
- Increased air stability.
- Fog can develop.
- Temperature inversions are possible.
Fronts
- Boundaries between air masses
- Cold front
- Warm front
- Stationary front
- Occluded front
Discontinuities
- Identifying frontal passage: temperature/pressure/wind changes
Cold Front
- Characteristics, including cloud formations, typical weather conditions.
Cold Front Weather
- Prior, during, and after cold-front passage conditions for clouds, precip, winds, visibility, temperature, and dewpoint.
Warm Front
- Characteristics, including cloud formations, typical weather conditions
- Weather changes: prior to, during, and after warm-front passage
Stationary Front
- Relative balance of opposing air masses, extended duration.
- Mix of cold and warm front characteristics.
Occluded Front
- Fast-moving cold front catches up to slower-moving warm front.
- Two types of occlusions
- Cold front occlusions
- Warm front occlusions
Occluded Fronts continued
- Characteristics, typical weather conditions.
Occluded Front Weather
- Prior, during and after passage conditions for clouds, precipitation, visibility, winds, temperatures, and dewpoint
Thunderstorms
- Needed for development: unstable conditions, lifting force, high moisture levels
- Two types: airmass and severe
- T-storm types: single-cell, super-cell, multi-cell, squall line, frontal
- Life cycle: cumulus, mature, dissipating.
T-storm Hazards - Turbulence
- Cumulonimbus clouds are highly turbulent.
- Turbulence between updrafts and downdrafts, and low-level turbulence from downdrafts spreading.
T-storm Hazards - Lightning
- Lightning always associated with thunderstorms.
- In-cloud
- Cloud-to-cloud
- Cloud-to-ground
- Cloud-to-clear air
- Risks of damage to aircraft or personnel
T-storm Hazards - Hail
- Can happen at all altitudes, either inside or outside of clouds.
- Potential for damage to aircraft
T-storm Hazards - Tornadoes
- Funnel cloud descending from cloud base, impacting land or water.
- Strong winds possible
Turbulence
- Turbulence in and near thunderstorms, low-level, clear air, mountain wave.
- Pilot actions during turbulent conditions.
Low-level Turbulence
- Below 15,000 ft.
- Associated with surface heating or friction
- Four types: mechanical, convective, frontal, wake.
Mechanical Turbulence
- Obstacles interfering with wind flow
- Edities around obstacles (trees, buildings).
- Downwind of obstructions
Convective Turbulence
- Thermal turbulence during daytime
- Warmer surface heats air
- 200 to 2000 FPM updrafts.
- Towering cumulus clouds signify convective activity.
- Stable layer above can produce haze/dust
- Potential for turbulence.
Frontal Turbulence
- Ahead of cold fronts, moderate to severe.
- Up to 1000 feet per minute vertical.
Wake Turbulence
- Wingtip vortices generated during lift.
- Intensity depends on aircraft weight, speed, and configuration
- Large planes at low speeds generate significant wake turbulence.
Wake Turbulence continued
- Vortices sink below the flight path.
- Most dangerous just after/below the aircraft.
- ATC separation procedures for avoiding wake turbulence.
Avoiding Wake Turbulence
- Recommended procedures: following distances behind aircraft, considerations for direction/speed differences, recommended flight paths based on wind conditions
Jet Engine Blast
- Hazard for small planes behind jet aircraft
- Stay several hundred feet away.
Clear Air Turbulence (CAT)
- Above 15,000 feet.
- Often occurs around jet streams or high-wind areas near the tropopause
- No immediate visual warnings.
Mountain Wave Turbulence
- Stable air over mountains
- Smooth over the windward side
- High winds perpendicular to ridgelines create disturbance.
- Significant wave extension downwind.
- Upper air turbulence as air flows around high peaks
Mountain Wave Turbulence continued
- Signature clouds form as evidence.
-Rotor clouds
- Lenticular clouds
- Avoiding mountain wave turbulence
- Approach at angles (45 degrees)
- Consider prevailing wind conditions.
Wind Shear
- Sudden shift in speed or direction.
- Frontal systems, thunderstorms, temperature inversions, clear air turbulence, jet streams are associated.
- Potential dangers are loss of control/altitude and increased difficulty for aircraft.
Microburst
- Strong downdraft.
- Horizontal spread is less than a nautical mile often.
- Significant vertical spread
Low-Level Wind Shear Alert Systems (LLWSAS)
- Wind sensors at airports detect wind differences.
- Computer analysis detects wind shear.
- ATC gives alerts and information.
Terminal Doppler Weather Radar (TDWR)
- Radar for higher resolution of thunderstorms.
Visual Indications of Wind Shear
- Rain shaft
- Virga
- Dust ring on ground
Icing
- Visible moisture necessary for structural icing.
- Freezing rain generates accumulation quickly.
- Aircraft surface at 0° Celsius or below increases icing risk.
- Effects in terms of lift and drag
- Icing on aircraft can drastically reduce performance and cause risk of control issues/damage
Types of Ice
- Rime ice – typically white
- Forms in stratus clouds
- Supercooled water droplets
- Clear ice – typically clear
- Freezing rain under a warm front inversion.
Types of Icing continued
- Mixed ice -Combo of rime and clear ice
- Important to consider for pilots in icy weather to prevent damage/loss of control in flight.
Restrictions to Visibility
- Haze: fine particles, stable atmosphere, decreased visibility compared to stable conditions above
- Smoke: airborne combustion particles, orange/reddish colors
- Smog: combo of fog and smoke, trapped in valleys or regions of stable air, reduced visibility
- Dust: fine soil particles, strong winds, unstable atmosphere, poor visibility
Volcanic Ash
- Highly abrasive.
- Impacts windscreens and landing lights.
- Clogs pitot/vent systems, potentially damaging control surfaces
- Engines are at greater risk of damage.
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Test your knowledge on clouds and precipitation with this engaging quiz. Discover the various types of clouds, their characteristics, and the conditions favorable for their formation. Perfect for students and enthusiasts of meteorology!
