Weather Academics Flashcards
Natural Air Formula
Dry Air + Condensation Nuclei + Water Vapor
Where in the atmosphere does weather occur?
Troposphere
Between the 30° - 60° N latitude where the U.S. is located, what is the prevailing wind direction?
Westerly
Three Cell Theory of Circulation
- Uneven heating of sun
- Coriolis force
- Tilt of earth
What direction does low pressure on northern hemisphere rotate?
Counterclockwise
What direction does high pressure on northern hemisphere rotate?
Clockwise
Water Vapor Content -
c =
m =
c = Continental Air Mass (Dry)
m = Maritime Air Mass (Moist)
Temperature -
A =
P =
T =
E=
A = Arctic Air Mass (Freezing)
P = Polar Air Mass (Cold)
T = Tropical Air Mass (Warm)
E = Equatorial Air Mass (Hot)
Four Methods of Heat Transfer
- Radiation
- Conduction
- Convection
- Advection
How is heat transfered through radiation?
As Electromagnetic Waves
What is insolation?
Radiation from the Sun to the Earth
What is terrestrial radiation?
Radiation leaving Earth into space
Temperature Inversion
A layer of air characterized by an increase in temperature by altitude
Two Types of Temperature Inversion
Nocturnal and Frontal
Difference between Convection and Advection
Convection is the vertial transfer while Advection is horizontal
In the late evening, a thick layer of clouds have moved over your airfield. Will a nocturnal happen this evening?
No it will not because the clouds prevent inversion from happening by keeping the warmer air near the surface.
Standard Day Pressure
29.92” Hg
1013.2 hP/mb
How is change in pressure depicted on a weather chart?
Isobars which are generally drawn 4 mb apart
Pressure Gradient Force
Rate at which air will accelerate depends on rate at which pressure changes with distance
Strong Pressure Gradient Force is
Isobars are closely spaced together
Weak Pressure Gradient Force
Isobars are separated further apart
In theory, at what altitude does surface friction occur?
2,000ft AGL
When below 2,000ft AGL how are the winds changed when surface friction is applied?
High Pressure:
Low pressure:
- High pressure: The winds diverge away from the center
- Low pressure: The winds converge towards the center
What is High Pressure on the Northern Hemisphere called?
Anticyclone
What is Low Pressure on the Northern Hemisphere called?
Cyclone
What indication tells you what pressure you are flying into?
Low Pressure = Left Crosswinds
High Pressure = Right Crosswinds
Deposition
Gas goes to solid without being a liquid first
Sublimation
Solid goes to gas without being a liquid first
How is flight performance affected by moisture in the atmosphere?
Less air density = higher density altitude = reduction in lift
Three atmospheric conditions that provide best lift?
- High Pressure
- Low Temperature
- Low Humidity
Adiabatic Process
When the temperature of a gas is changed without the addition or deletion of heat energy
Dry Adiabatic Lapse Rate
3°C / 1,000ft
Moist Adiabatic Lapse Rate
1.5°C / 1,000ft
An example of Adiabatic Process
Air being lifted over a mountain range will cool climbing on the windward side and heat up as it moves downslope on the leeward side.
LCL
Lifted Condensation Level
Lifted Condensation Level
Rising air temperature is the same as the dew point temperature and clouds are formed
LFC
Level of Free Convection
Level of Free Convection
Where the rising air temperature is the same as the ambient air temperature
Clouds in low altitude in an unstable environment?
Cumuliform
Clouds in low altitude in a stable environment?
Stratiform
Low Clouds
(Within 6,500ft AGL)
Cumulus - CU
Stratus - ST
Stratocumulus - SC
Cumulonimbus - CB
Middle Clouds
(6,500ft - 20,000ft AGL)
Altostratus - AS
Altocumulus - AC
Nimbostratus - NS
High Clouds
(16,000ft to 45,000ft AGL)
Cirrus - CI
Cirrostratus - CS
Cirrocumulus - CC
What would you expect to happen to wind direction and speed during a frontal passage?
90° shift in wind and wind speed is based upon current pressure gradient force
What happens as warm air is lifted over a cold air mass?
It lifts, cools with altitude, condenses, creates clouds and “makes weather”.
What can you expect to see if a cold front is moving really fast?
A squall line
Which front has temperature inversion?
All of them
Cause of Frontal Weather
Lifting warm air over cold air
The entire local flying area is covered in ST, NS, and AS clouds. What type of front is occuring?
Stable warm front
You are approaching the clouds in the following order: CS, AS, and NS. What changes can you expect?
Ceiling and visibility decreasing, chance of precipitation increasing
Why is the occluded front considered more complex?
Combination of both cold and warm front weather
Flight Procedure
Cold Front / Squal Lines
Land and wait
Flight Procedure
Warm Front / Stationary Front
Prepare for alternate landing location
Flight Procedure
Frontal Wave
Handle each front individually
Flight Procedure
Occluded Fronts
Circumnavigate or land
Types of Fog
Radiation Fog
Advection Fog
Precipitation-Induced Fog
Upslope Fog
Freezing Fog
Ice Fog
What causes Radiation Fog?
Radiation cooling on clear, calm nights
What causes Advection Fog?
Warm, moist air moving over a cooler surface, deepens with wind between 3 - 9kts
What causes Precipitation-Induced Fog?
Precipitation falling through cool, unsaturated air
What causes Upslope Fog?
Moist, stable air being lifted by sloping terrain
What causes Freezing Fog?
When supercooled droplets contact a freezing surface
What causes Ice Fog?
Extremely cold temperatures and depositions <= -30°C
Types of Ice
Rime
Clear
Mixed
Frost
How is Frost formed?
Ice crystals formed by deposition of water vapor contacting a cold surface
How is Rime Ice formed?
Forms from small supercooled water droplets
How is Clear Ice formed?
Forms from large supercooled water droplets
How is Mixed Ice formed?
Formed as a combination of rime and clear ice
How is Freezing Rain formed?
Rain droplets fall through a frontal inversion into a layer of air which has sub-zero temperature
Categories of Ice Intensity
- Trace
- Light
- Moderate
- Severe (Immediate Diversion)
Severe Icing Altitudes
10,000ft MSL to 18,000ft MSL
Icing Hazards
- Loss of autorotative capability
- Reduces lift
- Increases drag and weight
- Reduces speed at which the rotor will stall
- Reduces visibility when ice forms on windshield
- Reduces air flow to engines when ice forms on screens
- Pitot and / or static source icing results in instrument error
Thunderstorm Development Factors
- Unstable or conditionally unstable air
- High moisture content
- Lifting action
Thunderstorm Types
- Air Mass
- Orographic
- Frontal
Air Mass Thunderstorm Cause
Caused by thermal convective activity; surface heating
Orographic Thunderstorm Cause
Terrain Effects
Frontal Thunderstorm Cause
- Cold Front; Squall Lines
- Warm Front
- Stationary Front
- Occluded Front
Thunderstorm Developmental Stages
- Towering Cumulus
- Mature
- Dissipating
What is a microburst?
Short-lived powerful downburst associated with convective activity
Define IFR conditions by ceiling and visibility
Ceiling 500ft AGL to less than 1,000ft AGL
AND / OR
Visibility 1SM to less than 3SM
Winds for Warm Front
Behind - Southwest
In Front - South East
Winds for Cold Front
Behind - Northwest
In Front - Southwest
What are the hazards associated with an outflow boundary?
- Gusting Wind
- Wind Shift
- Low-level Wind Shear
- Turbulence
- Possible Storm Development
