Pressure And Density

Question 1

Explain what’s meant by partial pressure of gas

Answer 1

Air is made up of different gases
•Each has its own partial pressure
•When they are all added together that is the pressure we feel

Question 2

Explain significance of air pressure with reference to barometric tendency and altimetry

Answer 2

Barometric tendency - change in atmospheric pressure over a given time frame. Caused by atmopsheric/solar tide or pressure change from development/decay of weather

Altimetry - reads difference in pressure.

Question 3

Define pressure gradient

Answer 3

Change of horizontal pressure over a distance and acts at 90º to isobars.

Can tell wind speed by spacing.

Question 4

Describe the exceptions of transition layers

Answer 4

Transition level becomes FL16 if QNH is less than 980 or IMC within 20NM of mount cook.

Question 5

Exceptions of airspace.

Answer 5

Controlled airspace can fly at 14,000ft in emergency or due weather
•Designated NON STANDARD
•Uncontrolled IFR may use layer if unable to operate outside of range
•Still have to notify ATS unit and no traffic conflict

Question 6

Why are transition layers in other country’s found at lower or higher levels in the atmopshere

Answer 6

Based on minimum safe altitude (MSA) in country
•Takes into account the surface terrain for example large mountains
•In the USA and Canada, the transition altitude is 18,000ft
•Europe has transition altitudes of 3000-6000ft

Question 7

Describe how localised pressure changes occur in association with Lee troughs.

Answer 7

Low pressure created on lee of mountain
•Relatively high pressure built up on windward side of mountain
•Like the high pressure on front of aircraft and low pressure at back

Question 8

Describe how localised pressure changes in association with thermal/heat lows

Answer 8

A thermal low is a shallow pressure system caused by the sun’s heating of a land mass esp in summer.

• One surface heats up more than others in the area and causes the hotter surface to drop in pressure due to convection

•Ocean and land heat up at different speeds
•Large shadows cast over an area by cloud/land and direct sun in another

Question 9

Describe how pressure changes with thunderstorms

Answer 9

• Under the updrafts pressure decreases by 2-3hPa
  •Under precipitation/downdrafts pressure increases by 2-3hPa
  •Due to rain evaporating which cools air and makes it heavier

Question 10

Describe diurnal pressure variations

Answer 10

Measure of surface pressure level over 24 hours
•Max pressure 10am and 10pm
•Min pressure 4am and 4pm
•Lowest at 4pm, highest at 10am

Question 11

State latitudes where diurnal variation is most signficant

Answer 11

Larger changes at low latitudes due larger change in temperature
•Local pressure systems dominate in NZ, variation unnoticeable
•Most noticeable in tropical regions
•Between tropic of Cancer and Capricorn 23°26’N/S

Question 12

Explain the effects of changes in pressure on air density.

Answer 12

Air density is the mass per unit volume of air in terms of weight per unit of volume

Increase pressure = increase density

Decrease pressure = decrease density

Question 13

Explain the effect of changes in temperature on air density.

Answer 13

Increase temperature = decrease density

Decrease temperature = increase density.

Question 14

Explain the effects of altitude on density

Answer 14

Increase altitude = decrease density
Decrease altitude = increase density

Question 15

Explain the effects of moisture content in the air on air density

Answer 15

Increase moisture = decrease density

Decrease moisture = increase density.