Weather 1: Weather Theory Flashcards
What is the troposphere?
The layer adjacent to the Earth’s surface
Average height of 55,000 ft. over the equator and average height of 28,000 ft. over the poles
What is the make up of the Earth’s atmosphere?
- 78% Nitrogen
- 21% Oxygen
- 1% Other
What is the average height of the troposphere over the US?
36,000’ MSL
Where does nearly all weather on Earth occur?
In the troposphere
What is the tropopause?
It’s the transition zone between troposphere and stratosphere
What is the relationship between altitude and temperature in the troposphere?
Temperature normally decreases as altitude increases
What is the relationship between altitude and temperature in the tropopause?
Temperature is constant as altitude increases
Where does jet stream winds occur?
Just below the tropopause (in the troposphere)
Atmospheric Pressure
The pressure exerted on a surface, by the atmosphere, due to the weight of the column of air directly above that surface
What are the units of measurement for pressure?
- Inches of mecury (in-Hg)
- Milibars (mb)
Station pressure
The atmospheric pressure measured directly at an airfield/weather station
Sea level pressure
Pressure that would be measured from the existing weather if the station were at mean sea level
Why do all stations report sea level pressure instead of station pressure?
If station pressure were used by everyone then maps would depict reverse topography
Meaning that stations at high altitudes would report lower pressure
What is the primary reason that atmospheric circulation takes place?
Ascending and descending air currents due to heating and cooling of the earth’s surface
Pressure gradient
The rate of pressure change in a perpendicular direction across the isobars
Pressure gradient force
The initiating force for all winds
Strength of the PGF is depicted by space between isobars
What does tight spacing between isobars mean?
- Steep pressure gradient
- Strong PGF
- Faster winds
What does wide spacing between isobars mean?
- Shallow pressure gradient
- Weak PGF
- Slower winds
What are the standard day pressure and temperature conditions?
- 29.92 in-Hg (pressure)
- 15° C (temperature)
What are the standard day lapse rates?
- A decrease of 1 in-Hg per 1000 ft. increase in altitude (pressure lapse rate)
- A decrease of 2°C per 1000 ft. increase in altitude (temperature lapse rate)
Air Mass
A large body of air that has essentially uniform temperature and moisture conditions in a horizontal plane (same conditions for a given altitude)
Saturation
The point in which the air contains the max amount of water vapor it can hold for that temperature
Dew Point Temperature
The temperature at which saturation occurs
Dew Point Depression (Dew Point Spread)
The difference between the air temperature and the dew point temperature
(The smaller the spread/difference, the closer the atmosphere is to the point of saturation)
When you see a 2°C dew point spread, that is where you start to see visible moisture like fog
Relative Humidity
The percent of saturation in the air
What are the different types of altitude?
- Indicated altitude
- True altitude (Mean Sea Level)
- Absolute altitude (AGL)
- Pressure altitude
- Density altitude
Indicated Altitude
Altitude read from the altimeter
Calibrated Altitude
Indicated altitude corrected for instrument error
True Altitude (Mean Sea Level)
The actual height above mean sea level
Absolute Altitude (AGL)
The aircraft’s height above the terrain directly beneath the aircraft
Pressure Altitude
The height above the standard datum plane (where the pressure is 29.92 in-Hg above/below the Earth’s surface)
FAR requires that aircraft above 18,000’ MSL use 29.92 in-Hg as their altemeter setting and are assigned “flight levels”
Density Altitude
An index to aircraft performance (instead of a height reference)
Pressure altitude corrected for non-standard temperature deviations
What is the relationship between air density and density altitude?
Inverse relationship; if air density increases, then density altitude decreases
How is aircraft performance affected by a high density altitude?
- Decreased thrust
- Decreased lift
- Longer takeoffs and landings
How is aircraft performance affected by a low density altitude?
- Increased thrust
- Increased lift
- Shorter takeoffs and landings
How does going from a high pressure area to a low pressure area affect your altimeter?
- The indicated altitude on the altimeter is higher than the aircraft’s actual position
- The aircraft’s altitude is actually lower than the indicated altitude
“High to low, look out below.”
How does going from a low pressure area to a high pressure area affect your altimeter?
- The indicated altitude on the altimeter is lower than the aircraft’s actual position
- The aircraft’s actual altitude is actually higher than the indicated altitude on the altimeter
“Low to high, plenty of sky.”
What happens to the altimeter is the air temperature is colder than standard?
- The indicated altitude on the altimeter is higher than the aircraft’s actual position
- The aircraft’s altitude is actually lower than indicated altitude
What happens to the altimeter is the air temperature is warmer than standard?
- The indicated altitude on the altimeter is lower than the aircraft’s actual position
- The aircraft’s altitude is actually higher than the indicated altitude
