Weather 1: Weather Theory

Question 1

What is the troposphere?

Answer 1

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

Question 2

What is the make up of the Earth’s atmosphere?

Answer 2

• 78% Nitrogen
• 21% Oxygen
• 1% Other

Question 3

What is the average height of the troposphere over the US?

Answer 3

36,000’ MSL

Question 4

Where does nearly all weather on Earth occur?

Answer 4

In the troposphere

Question 5

What is the tropopause?

Answer 5

It’s the transition zone between troposphere and stratosphere

Question 6

What is the relationship between altitude and temperature in the troposphere?

Answer 6

Temperature normally decreases as altitude increases

Question 7

What is the relationship between altitude and temperature in the tropopause?

Answer 7

Temperature is constant as altitude increases

Question 8

Where does jet stream winds occur?

Answer 8

Just below the tropopause (in the troposphere)

Question 9

Atmospheric Pressure

Answer 9

The pressure exerted on a surface, by the atmosphere, due to the weight of the column of air directly above that surface

Question 10

What are the units of measurement for pressure?

Answer 10

1. Inches of mecury (in-Hg)
2. Milibars (mb)

Question 11

Station pressure

Answer 11

The atmospheric pressure measured directly at an airfield/weather station

Question 12

Sea level pressure

Answer 12

Pressure that would be measured from the existing weather if the station were at mean sea level

Question 13

Why do all stations report sea level pressure instead of station pressure?

Answer 13

If station pressure were used by everyone then maps would depict reverse topography

Meaning that stations at high altitudes would report lower pressure

Question 14

What is the primary reason that atmospheric circulation takes place?

Answer 14

Ascending and descending air currents due to heating and cooling of the earth’s surface

Question 15

Pressure gradient

Answer 15

The rate of pressure change in a perpendicular direction across the isobars

Question 16

Pressure gradient force

Answer 16

The initiating force for all winds

Strength of the PGF is depicted by space between isobars

Question 17

What does tight spacing between isobars mean?

Answer 17

1. Steep pressure gradient
2. Strong PGF
3. Faster winds

Question 18

What does wide spacing between isobars mean?

Answer 18

1. Shallow pressure gradient
2. Weak PGF
3. Slower winds

Question 19

What are the standard day pressure and temperature conditions?

Answer 19

• 29.92 in-Hg (pressure)
• 15° C (temperature)

Question 20

What are the standard day lapse rates?

Answer 20

• 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)

Question 21

Air Mass

Answer 21

A large body of air that has essentially uniform temperature and moisture conditions in a horizontal plane (same conditions for a given altitude)

Question 22

Saturation

Answer 22

The point in which the air contains the max amount of water vapor it can hold for that temperature

Question 23

Dew Point Temperature

Answer 23

The temperature at which saturation occurs

Question 24

Dew Point Depression (Dew Point Spread)

Answer 24

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

Question 25

Relative Humidity

Answer 25

The percent of saturation in the air

Question 26

What are the different types of altitude?

Answer 26

* Indicated altitude * True altitude (Mean Sea Level) * Absolute altitude (AGL) * Pressure altitude * Density altitude

Question 27

Indicated Altitude

Answer 27

Altitude read from the altimeter

Question 28

Calibrated Altitude

Answer 28

Indicated altitude corrected for instrument error

Question 29

True Altitude (Mean Sea Level)

Answer 29

The actual height above mean sea level

Question 30

Absolute Altitude (AGL)

Answer 30

The aircraft's height above the terrain directly beneath the aircraft

Question 31

Pressure Altitude

Answer 31

The height above the standard datum plane (where the pressure is 29.92 in-Hg above/below the Earth's surface) ## Footnote FAR requires that aircraft above 18,000' MSL use 29.92 in-Hg as their altemeter setting and are assigned "flight levels"

Question 32

Density Altitude

Answer 32

An index to aircraft performance (instead of a height reference) ## Footnote Pressure altitude corrected for non-standard temperature deviations

Question 33

What is the relationship between air density and density altitude?

Answer 33

Inverse relationship; if air density increases, then density altitude decreases

Question 34

How is aircraft performance affected by a **high density altitude**?

Answer 34

* Decreased thrust * Decreased lift * Longer takeoffs and landings

Question 35

How is aircraft performance affected by a **low density altitude**?

Answer 35

* Increased thrust * Increased lift * Shorter takeoffs and landings

Question 36

How does going from a **high pressure area to a low pressure area** affect your altimeter?

Answer 36

* 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 ## Footnote "High to low, look out below."

Question 37

How does going from a **low pressure area to a high pressure area** affect your altimeter?

Answer 37

* 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 ## Footnote "Low to high, plenty of sky."

Question 38

What happens to the altimeter is the air temperature is **colder** than standard?

Answer 38

* The indicated altitude on the altimeter is higher than the aircraft's actual position * The aircraft's altitude is actually lower than indicated altitude

Question 39

What happens to the altimeter is the air temperature is **warmer** than standard?

Answer 39

* 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