Ch 3 - Atmospheric Pressure Flashcards Preview

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Flashcards in Ch 3 - Atmospheric Pressure Deck (39):
1

What causes pressure?

Force exerted on a unit of surface area (i.e. 1 hPa = 100 newtons per square meter)

2

What causes atmospheric pressure?

Weight of air acting in all directions

3

What causes pressure in the atmosphere?

The sun

4

What is the standard unit of pressure?

Pascal (Pa)

Hectopascal (hPa) = 100 Pa

5

What happens to pressure with altitude?

Decreases

(due to a lower mass of air above)

6

What deviced measure pressure?

- Mercury barometer
- Aneroid barometer
- Aneroid barograph
- Solid-state pressure sensors

7

What causes changes in pressure?

Changes in mass of the air above (i.e. as it moves around)

8

What is QFE?

Pressure at the airfield/fixed datum point

Altimeter will read 0 on the ground

9

What is QNH?

QFE adjusted to MSL

Altimeter will read airfield elevation on the ground

10

What is QFF?

QFE adjusted to MSL, taking temperature into account

11

What is SPS/QNE?

Standard pressure setting 1,013.25

What the altimeter will read when set to 1,013.25

12

What are pressure levels?

Horizontal expanses of equal pressure. Pressure levels change vertically.

(imagine a blanket which drapes around the planet at a particular pressure; it will be contoured as that same pressure differs in altitude across the planet)

13

What happens to pressure levels in warmer air?

Vertical gaps between them expand

14

What happens to pressure levels in colder air?

Vertical gaps between them contract

15

At the same level, will pressure in a column of warm air be higher or lower than pressure in a column of cold air?

Higher

(cold air is denser and more of it falls, so pressure is lower because there is not as much air above the level)

16

Pressure lapse rate at MSL?

27ft / hPa

17

Pressure lapse rate at 500 hPa?

50ft / hPa

18

How do you calculate the pressure lapse rate?

96 x Temp (k)
___________
Pressure (hPa)

19

Are pressure and density at MSL high or low?

High

20

Are pressure and density at high altitude high or low?

Low

21

What happens to true altitude when going from high pressure to low pressure?

Decreases

FROM HIGH TO LOW, LOOK OUT BELOW!

22

What are isobars and what pressure reading do they connect?

Lines joining areas of equal pressure (QFF)

23

What to isobars enclose?

Areas of low or high pressure

24

In the northern hemisphere, which way does wind flow around isobars which enclose high pressure areas?

Clockwise

25

In the northern hemisphere, which way does wind flow around isobars which enclose low pressure areas?

Counter-clockwise

26

How much of the atmosphere's mass lies in the first 11 km / 36,000 ft?

75%

27

What is a Pressure Gradient Force (PGF)

A force driving air from an area of high pressure to an area of low pressure

28

What is wind caused by?

Horizontal differences in pressure

29

What can you predict from isobars close together?

High winds

30

What can you predict from isobars far apart?

Low winds

31

What are troughs?

Channels of low pressure between isobars

32

What are ridges?

Channels of high pressure between isobars

33

What are isohypses?

Lines joining the same true altitude of equal pressure

34

What are isohypses usually labelled in?

Decameters

35

What do lower isohypses usually indicate?

Colder air

36

What do higher isohypses usually indicate?

Warmer air

37

When will QFF be higher than QNH?

When the outside air temperature is not hotter than ISA

38

What weather can be expected from a low-pressure system?

- Good visibility
- Significant cloud
- Significant rain / precipitation
- Small diurnal changein temperature

39

What weather can be expected from a high-pressure system?

- Light winds
- Fog / mist / haze
- No rain / precipitation
- Large diurnal change in temperature