NIFE Weather 6-1-2 Theory

Question 1

2.172

Describe the characteristics of the troposphere

Answer 1

• Ave 36000’ AGL (28k over poles-55k over equator)
• Nearly all weather occurs
• Temp decreases with altitude increase
• Wind increases with altitude
• Top is the tropopause

Question 2

2.173

Define atmospheric pressure

Answer 2

• Weight of a column of air over an area on Earth’s surface
• 29.92 inHg
• 1013 millibars
• always decrease with an increase in altitude

Question 3

2.174

State the standard units of pressure measurement

Answer 3

• 29.92 inHg

- 1013 millibars

Question 4

2.175

Explain the term pressure gradient

Answer 4

• Initiating force for all winds
• Air wants to flow from high to low pressure
• Force acts perpendicular to isobars
• Strength is represented by isobars: Tight= strong winds, Wide= weak winds

Question 5

2.176

Define a lapse rate

Answer 5

A standard decrease of temperature inversely related to an increase in altitude. Relatively constant (except for special circumstances) up to the isothermal layer.

Question 6

2.177

State the average temperature lapse rate in degrees Celsius. Pressure lapse rate?

Answer 6

• Temp 2 C/1000ft
• Pressure 1 inHg/1000ft
• Both decrease with altitude

Question 7

2.178

Define the standard atmosphere.

Answer 7

• 21% oxygen
• 78% nitrogen
• 1% other gases
• water vapor can be 0-5%
• constant lapse rate

Question 8

2.179

Differentiate between sea level pressure and station pressure.

Answer 8

-Pressure will always be less than sea level pressure if the station is higher in altitude.

Sea Level Pressure= Station Pressure + Field Elevation

Question 9

2.180

Define the types of altitudes

Answer 9

Indicated altitude: As read on altimeter

Absolute altitude: Above ground level (AGL)

True altitude: Above Mean Sea Level (MSL)

Pressure altitude: Above Standard Datum Plane

Density Altitude: Pressure altitude corrected for non-standard temperatures

• • Density decreases, DA increases
• • Indicator of aircraft performance, Not a height reference

Question 10

2.181

Define indicated altitude

Answer 10

-What is read on the altimeter

Question 11

2.182

Describe the effects of pressure changes on aircraft altimeters

Answer 11

-A change of pressure of 1 inHg will change the altimeter reading 1000ft

“High to low, look out below”

“Low to high, plenty of sky”

Question 12

2.183

Describe the effects of temperature deviations from the standard lapse rate on aircraft altimeters

Answer 12

-Density Altitude: Pressure altitude corrected for nonstandard temperature.

Question 13

2.184

Define the term air mass

Answer 13

• A large mass of air with the same characteristic in a horizontal plane (temperature and moisture)
• Stable-warm
• Unstable-cold

Question 14

2.197

Define saturation

Answer 14

-The amount of moisture that can be held in the air

Question 15

2.198

Define dew point temperature and depression

Answer 15

• Temperature where saturation occurs
• Dew point temperature is always lower than or equal to the current temperature.
• Depression is the difference between the air temperature and the dew point temperature

Question 16

2.293

Explain why atmospheric circulation occurs

Answer 16

• Constant heating and cooling of the Earth’s surface

- Coriolis Effect: Everything deflects to the right (West to East in the northern hemisphere)

Question 17

2.294

Define a temperature inversion

Answer 17

• Air temperature increases with increase in altitude

- Special occasion (Dangerous)

Question 18

2.295

Define relative humidity

Answer 18

• Not a direct measurement of the actual amount of water vapor/ moisture in the air, only the actual amount in the air compared to the total amount that could be present
• Warmer air holds more than cold air