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ATPL Meteorology > Pressure > Flashcards

Pressure Flashcards

1
Q

The atmosphere is composed of a variety of gases these are….

A

Nitrogen (78%)
Oxygen (21%)
Carbon Dioxide (0.04%)
Other

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2
Q

What is atmospheric pressure defined as?

A

Combined weight of gases exerting force in all directions

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3
Q

What is used to measure atmospheric pressure?

A

A Barometer

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4
Q

What is pressure expressed as?

A

Inches or Millibars of Mercury
Millibar
Hectopascal

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5
Q

A hectopascal is equal to…

A

100 newtons per square metre

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6
Q

What is an isobar?

A

The line on the map to indicate locations of the same pressure

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7
Q

What happens to pressure as you increase altitude?

A

Reduces

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8
Q

What is the ISA pressure at sea level?

In HPA, Hg and lb/sq.in

A
  1. 25 HPA
  2. 92Hg
  3. 7lb/sq.in
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9
Q

What is QNE (Question Nil Elevation)?

A

Setting 1013 on aircraft subscale

QNE is a pressure setting of 29.92 inches or 1013 hPa that will produce a standard atmosphere altitude and provides the basis for flight levels.

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10
Q

With QNE set on the altimeter, the main scale will indicate?

A

Height above or below 1013 HPA Pressure level

Pressure height or Pressure Altitude

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11
Q

At low level, the pressure reduces at a rate of…

A

1 HPA / 30ft of altitude increase in the troposphere

=1 Hg / 1000ft

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12
Q

Air density refers to….

A

Mass of air occupying a given volume

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13
Q

What 3 factors does air density depend on?

A
  • Temperature
  • Humidity
  • Pressure
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14
Q

Decreased Pressure= …. Density

A

Decreased Density

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15
Q

Increased Temperature=

A

Decreased Density

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16
Q

Increased Humidity=

A

Decreased Density

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17
Q

Does high density give better or worse aircraft performance?

A

Better

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18
Q

Why do variations in pressure occur?

A
  • The movement of pressure systems
  • Changing the intensity of pressure systems
  • Semi diurnal Pressure variation
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19
Q

What is semi-diurnal variation?

A

Rhythmic variation in pressure over 12 hour period

20
Q

Where is semi-diurnal variation the greatest?

A

Tropics

Can change up to 5 HPA

21
Q

What is standard pressure?

A

1013.25 HPA

22
Q

What is the actual mean sea level pressure referred to as?

A

QNH

23
Q

When QNH is set on altimeter it will read…

A

Altitude (Height above mean sea level)

24
Q

What is local QNH?

A

Actual sea level pressure for a particular location

25
Q

Where is Local QNH available?

A

Control tower or ATIS

26
Q

If you set the airfield elevation on your altimeter what will it read?

A

Approx. Local QNH

27
Q

What is area QNH?

A

Predicted average sea level pressure

28
Q

Who forecasts area QNH?

A

Bureau of Meteorology

29
Q

How often is area QNH updated?

A

Every 3 hours

30
Q

Area and Local QNH can differ, but by how much?

A

5 HPA

31
Q

In Australia, pilots cruise on local QNH up to what distance?

A

100nm

When cruising at or below 10,000ft

32
Q

What is a transition layer?

A

Between A100 and FL110-FL125 depending on QNH; separates aircraft on QNH to aircraft on standard pressure
(Cruise not permitted in this layer)

33
Q

Heights are expressed as..

A

Hundreds of feet prefixed A for altitudes on QNH; FL for those on pressure altitudes referenced to standard pressure

34
Q

What is QFE?

A

Station level pressure

35
Q

With QFE on subscale the main scale will read…

A

Height above or below reference pressure point

36
Q

How to obtain QFE?

A

Set 0 on aircraft subscale

37
Q

What is QFF?

A

Meteorological mean sea level pressure. Takes into account temperature and water vapour content.

38
Q

What is the common isobar spacing?

A

2-4 HPA

39
Q

An altimeter in an aircraft flying towards LOW PRESSURE will….

A

Over read

The altimeter cannot distinguish between falling surface pressure and climbing

40
Q

What is a low?

A

A centre of low pressure surrounded by higher pressure

41
Q

What is a High?

A

A centre on high pressure surrounded by low pressure

42
Q

What is a col?

A

A neutral area between two highs and two lows

43
Q

What is a trough?

A

Any elongated area of low pressure

44
Q

What is a ridge?

A

Any elongated area of high pressure

45
Q

How are pressure gradients measured?

A

From high to low pressure at right angles to the isobars

46
Q

What does close isobar spacing indicate?

A

Strong gradient and strong winds

47
Q

What does wide isobar spacing indicate?

A

Weak or shallow gradient and light winds

ATPL Meteorology (12 decks)

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