Weather Theory Flashcards
Atmospheric Composition
78% Nitrogen
21% Oxygen
1% Other
Troposphere
Lowest level of atmosphere.
Nearly all weather occurs here.
As altitude goes up temperature goes down.
Tropopause
Boundary between Troposphere and Stratosphere.
Stratosphere
Temp gradually increases as altitude goes up.
Standard Atmosphere
Datum for temperature and pressure at specific altitudes.
At sea level standard is:
15 Degrees C
29.92 hg
Lapse rate is every 1000ft up you drop 2 degrees C.
Indicators of Stable Atmosphere
Poor visibility
Stratiform Clouds
Continuous Precipitation
Absence of Turbulence
Indicators of UNstable Atmosphere
Good visibility
Cumuliform Clouds
Scattered Precipitation
Turbulent Air
Thunderstorms
What is convection?
Upward and downward movement of air.
Three forces affecting wind heading and speed?
Pressure Gradient Force
Coriolis Force
Friction
How does pressure travel?
High to Low
Carries winds
What is Wind Shear?
Air Currents of differing velocities create friction or Shear between them. Inside the shear zone is a nasty mix of eddies and whirls.
Temperature Inversion
May exist anywhere
Most commonly found on clear, calm, cool nights.
The land cools more rapidly than the air, cooling the air directly above it faster than the air aloft.
May cause poor visibility.
May cause structural Icing.
What does evaporate mean?
Turn to vapor
What is humidity?
Moisture in the air
What is relative humidity?
Saturation level of the air, expressed as a %
What is Dew Point?
The Temperature at which the are would become 100% saturated by the moisture already present.
What is Temperature-Dew Point Spread?
Current Temperature - Current Dew Point
If spread is = 0 degrees, the relative humidity is 100%
Typically a Surface Spread Less than or equal to 5 degrees C will result in fog.
What is condensation?
Vapor to liquid
What is Sublimation?
Vapor straight to Ice
What is Super-Cooled Water?
Unfrozen water at a temperature below 0 degrees C
May freeze upon impact, causing structural icing.
If dew point is less than 0 deg C, water vapor tends to skip the liquid stage.
What is an Air Mass?
Large body of air having fairly uniform properties of temperature and moisture.
Types of Air Masses by Temperature?
Arctic - cold air formed over large bodies of ice or snow, typically at the poles.
Polar - cool air from the upper latitudes
Tropical - Warm air from the lower latitudes and equatorial areas.
Types of Air Masses by Moisture Content?
Continental - Formed over land,
Maritime - Formed over water.
5 Possible Classifications of Air Masses?
Continental Arctic - Cold, Dry
Continental Polar - Cold, Dry
Continental Tropical - Hot, Dry
Maritime Polar - Cool, Moist
Maritime Tropical - Warm, Moist
What is a Front?
Zone in between two Air Masses.
What might you experience at a Front?
Wind direction, speed or both may change rapidly.
Possible wind shear
Temperature changes rapidly
Pressure changes rapidly
Altimeter settings change rapidly
What is a Cold Front?
Leading edge of advancing cold air mass.
What happens when a cold air mass encounters a warm air mass at the surface?
A cold front will replace the less dense warm air mass.
What is a Warm Front?
Leading edge of advancing Warm air mass.
Typically move half as fast as a Cold Front.
What is an Occluded Front?
Faster Cold Front overtakes slower Warm Front.
What is a Squall Line?
Narrow band of fully developed Thunder Storms
What is a Dry Line?
Low Level Boundary separating moist air from dry air.
Height for low clouds?
Surface - 6500ft
Height for middle clouds?
6,500 - 23,000ft
Height for High clouds?
16,500 - 40,000ft
Cumulus clouds
Big, lumpy, billowy clouds
cumulus = accumulation
Result of convection
Typically indicate unstable atmosphere
Stratus clouds
Uniform, sheet like clouds
Result of stable air cooling
Nimbus clouds
Clouds from which rain is falling
Fractus clouds
clouds broken into fragments
High altitude clouds
Cirrus
Cirrocumulus
Cirrostratus
All typically thin and white in appearance
Mid Altitude Clouds
Altocumulus - wave pattern
Altostratus - Cover the sky allowing very little light.
Low altitude clouds
Stratus
Stratocumulus
Nimbostratus
Cumulus
Clouds with extensive vertical development
Towering Cumulus
Cumulonimbus
Convective Turbulence
Result of uneven heating of Earth’s surface
Mechanical Turbulence
Obstructions to wind flow causes turbulence
Mountain Wave turb
Wind forms a wave pattern after passing over mountain
Wake turbulence
Fall downward and outward
Carried by wind if any
What needs to be there for a Thunder storm to form?
Sufficient moisture
Unstable atmosphere
Updrafts
How do updrafts occur?
Surface heating
Winds pushed up sloping terrain
Converging winds
All of the above
Three stages of Thunder Storm
Cumulus
Mature
Dissipating
Cumulus Stage
Characterized by updrafts
Growth rate up to 3000 FPM
The cloud and rain drops grow in size
Mature Stage
Characterized by Precipitation, Updrafts, and Downdrafts.
Extremely powerful downdrafts = Microburst
Thunderstorm hazards reach greatest effect.
Dissipating Stage
Characterized by Downdrafts
Storm dies rapidly
No rain/downdrafts = no more thunderstorm
Microbursts
An extremely powerful downdraft
May occur anywhere thunderstorms, precipitation, or virga occurs.
Typically lasts 10 - 20 min
Most dangerous when landing
No known techniques can get you out of one.
Three types of icing?
Induction Icing
Instrument Icing
Structural Icing
Induction Icing
Ice accumulation blocking air from reaching the engine.
Instrument Icing
Icing of the pitot tube and or static source
Causes erroneous reading of:
- Airspeed Indicator (ASI)
- Altimeter
- Vertical Speed Indicator (VSI)
Structural Icing
Visible Moisture
Super-cooled water droplets may increase rate of structural icing.
Three Types:
- Clear - Forms when water droplet continues to spread, freezing slowly. Smooth sheet of heavy, and hard ice. Most dangerous.
- Rime - Formed by smaller droplets freezing rapidly. White, opaque appearance. Rough surface.
- Mixed - Combination of clear and rime ice. Heavy and rough.
PAIRUS Acronym for Fog
Precipitation
Advection
Ice
Radiation
Upslope
Steam
Precipitation fog
Forms as warmer precipitation falls through colder air, saturating the air as it evaporates.
Advection fog
Forms as moist air moves over colder ground or water.
Ice fog
fog composed of Ice cyrstals
Radiation fog
Terrestrial radiation from the cooling ground cools the air above it.
Upslope fog
Forms as moist stable air is pushed up sloping terrain.
Steam fog
Forms when cold air moves over warm water.
