Ch 3 - Atmospheric Pressure Flashcards

1
Q

Pressure

A

Pressure = Force / Area

Force = mass x acceleration

(Mass of molecules / Surface)

More air molecules = higher mass = higher pressure

Less air molecules = less mass = lower pressure

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

High Pressure System (Anti - cyclones)

A

More air in than out

  • High pressure on surface (Increases mass = Increased Pressure)
  • Low pressure at tropopause

Better weather, poor visibility

Lots of air converging at the top to fill the space left by other molecules

Molecules getting trapped at the bottom due to friction creating the increased mass and the increased pressure

Converges at the top, diverges at the bottom

High pressure air moves in a clockwise direction (N. Hemisphere)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Low Pressure System (Cyclones and Depressions)

A

More air out than in

  • High pressure at the tropopause
  • Low pressure on the surface 2/3000ft (low mass)

Converges at the bottom
Diverges at the top

Poor weather

Anti-clockwise direction (N. Hemisphere)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Measuring Pressure

A
  • Mercury Barometer
  • Aneroid Barometer
    - Much more reliable - Used on aircraft in altimeter
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Horizontal Pressure Variation

A

Horizontal Pressure Chart

  • Lines and pressures are Isobars
  • Indicate pressure at roughly 2/3000ft
  • How close the lines are together representing the pressure gradient force (closer together = greater gradient = Increased Force)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Vertical Pressure Variation

A

Pressure decreases with altitude at a non-linear rate due to gravity.

Levels Pressure(hPa). Rate of change of P

MSL 1013.25. 27
10,000. Roughly 700. 37
18,000. Roughly 500. 47
30,000. Roughly 300. 71
40,000. Roughly 200. 111.

ISA

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Pressure and Temperature

A

Cold air= Rate of change of pressure much quicker

Warm air = rate of change of pressure much slower

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Constant Pressure Charts

A

Colours Represent High/Low Pressure
- Known as Isohypes

  • Jet Streams are parallel to the isohypes
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

QNH

A

Question Nautical Height (above sea level)

QFE adjusted to MSL in ISA conditions (altimeters work off this hence temp errors)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

QFE

A

Question Field Elevation

  • Pressure at the station so that altimeters read 0 on the ground.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Elevation

A

Height of ground above MSL

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

QNE

A

Question Nautical Elevation - Indicated height on landing at an airfield with 1013hPa set (high airfields)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

QFF

A

= QFE adjusted to MSL in actual conditions

  • Do not use in aircraft
  • Is used on surface weather charts as it takes into account temperature
  • Works off actual temperatures
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Pressure Altitude

A

Altitude indicated when standard pressure 1013hPa set.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Flight Level

A

Used when above the transition altitude (usually 3/6000ft in the UK)

FL200 = 20,000ft

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Flight Levels

A

More dangerous when flying from high to low

High to Low, watch about below - clearance issue

Use the lowest useable one and the highest negative temperature deviation from ISA
- ensure clearance from terrain

17
Q

Warmer Than Isa Conditions

QNH and QFF

A

AMSL. BMSL

QNH>QFF. QFF>QNH

18
Q

Colder than ISA Conditions

QNH and QFF

A

AMSL. BMSL

QFF>QNH. QFF

19
Q

Datum Conversions

A

Wind off pressure, wind off altitude

20
Q

Barometric Error

A

Pressure set on altimeter sub scale, flying into an area of different pressure will lead to an error in true and indicated Altitude

High P -> Low P (look out below) Hot to cold, don’t be bold
IA will over read
TA will be lower

Low P -> High P
IA will under read
TA will be higher

21
Q

Temperature Error Correction (TEC) Formula

A

TEC = ( (ISA Dev/10) x 0.04)) x Altitude
(ft)

*Barometric Error first -> ISA and ISA deviation -> Temp error

22
Q

Effect of Temperature of Flight Level Separation Distance

A

If conditions are colder than ISA, Flight Level separation distance reduced

If conditions are warmer than ISA, Flight Level Separation distance increased