Met - Pressure, Density, Pr. Systems & Altimetry

Front 1

Definition of static pressure?

Back 1

The pressure caused solely by the effect of gravity on a mass of air

Front 2

Atmospheric Pressure definition?

Back 2

The name we give to the static pressure of the atmosphere during

Front 3

During clear weather pressure tends to be ________

Back 3

Higher

Front 4

During bad weather pressure generally tends to be ________

Back 4

Lower

Front 5

What are all forms of pressure defined as?

Back 5

A force per unit area

Front 6

What is the average atmospheric pressure on earth, or weight of air pressing down on us at sea level?

Back 6

1 bar or 14.7 lbs per in2

Front 7

Why is the highest pressure always felt at the surface?

Back 7

Because the entire atmosphere is above, and air is a fluid so has a mass. So within earths gravitational field the air exerts a weight force that bears down on the lower air and causes a higher static pressure

Front 8

How does an Anaroid barometer work?

Back 8

Uses a flexible, partially evacuated aneroid capsule. An increase in static pressure causes the capsule to contract. A decrease in static pressure causes it to expand due to air pressure inside it. The capsule is linked to a needle which indicates height or pressure

Front 9

How does a mercury barometer work?

Back 9

The earliest form of pressure measuring device, an evacuated tube filled with mercury. High atmospheric pressure exerts a force on the mercury and drives it up the tube. Low resource causes the mercury to overcome the force and drop.

Pressure is read as inches of mercury (inches hg)

Front 10

How does a solid state pressure sensor work?

Back 10

Uses a sealed, partially evacuated chamber. One end if the chamber has a diaphragm. Changes in ambient pressure cause the diaphragm to distort, and this is measured by piezoelectric strain gauges or by measuring the level of capacitance in the air gap

Front 11

What is piezo electricity?

Back 11

An electric charge that accumulated in certain solid materials in response to mechanical stress.

Electricity resulting from pressure and latent heat

Front 12

What is the SI unit measurement for pressure

Back 12

The Hectopascal hPa

Front 13

What is ISA MSL pressure?

Back 13

1013.25 mb or 29.92 inHg

Front 14

What is the formula for pressure?

Back 14

Pressure = force / Area

Front 15

What is atmospheric pressure change caused by?

Back 15

The mass of the overlying air

Front 16

The greater the mass of overlying air, the ________ the atmospheric pressure.

Back 16

Greater

Front 17

Does the temperature of the mass of air change the pressure that is exerted at the surface?

Back 17

No

Front 18

What are diagrams of variations in surface pressure called?

Back 18

Surface pressure charts or synoptic charts

Front 19

What is the common vertical datum used to measure surface pressure?

Back 19

Mean sea level

Front 20

What is QFF?

Back 20

Actual mean sea level pressure, corrected for actual temperature and pressure lapse rate.

Front 21

What is QNH?

Back 21

Observed barometric pressure at a station/Aerodrome reduced to MSL using ISA conditions

Front 22

What is QFE?

Back 22

Pressure at an Aerodrome/certain place (AGL)

Front 23

What are Isobars?

Back 23

Lines of equal pressure, on a synoptic chart.

Front 24

Which pressure datum is used to plot pressure on a synoptic chart?

Back 24

QFF

Front 25

What intervals are isobars drawn at?

Back 25

Usually 2-4 mb/hPa

Front 26

What is a low pressure area called?

Back 26

A depression or low

Front 27

What are areas of high pressure called?

Back 27

Anticyclones or highs

Front 28

How is an area of pressure defined as low or high?

Back 28

Relative to its surrounds, not on a set hPa reading

Front 29

In Europe, what does MSL pressure fluctuate between?

Back 29

950hPa to 1050hPa

Front 30

What is PGF?

Back 30

Pressure Gradient Force

Front 31

What is a pressure gradient force? (PGF)

Back 31

A force which drives air from an area of high pressure to and area of low pressure

Front 32

When does a PGF occur?

Back 32

Whenever there is a pressure variation.

Front 33

When is the pressure gradient force greatest?

Back 33

When there is a large difference in pressure between two places

Front 34

What causes wind?

Back 34

The horizontal differences in pressure, and the pressure gradient force driving the air from high to low areas. The great the difference in pressure, the greater the PGF and stronger the wind.

Front 35

What do isobars close together indicate?

Back 35

A strong PGF and strong winds

Front 36

What do widely spaced isobars indicate?

Back 36

A weak PGF and a resulting light wind

Front 37

In general what would isobars look like in an area of low pressure?

Back 37

Closely packed isobars

Front 38

In general what would isobars look like in an area of high pressure?

Back 38

Widely spaced isobars

Front 39

Why does pressure decrease with height?

Back 39

Because the higher we go, the less air there is bearing down on lower levels of atnosphere

Front 40

Why does pressure decrease with height?

Back 40

Because the higher we go, the less air there is bearing down on lower levels of atnosphere

Front 41

Why is most of the mass of air found in the lower levels of the atmosphere?

Back 41

Because air is compressible

Front 42

Pressure ________ with height at a __________ rate

Back 42

Decreases with height at a decreasing rate

Front 43

Why does pressure decrease with height at a slower rate at altitude

Back 43

Because there is less mass of air, and therefore less pressure variation in a given volume of

Air

Front 44

What is the formula to calculate change in height in ft, for every 1 hPa change of pressure? (Pressure Lapse Rate)

Back 44

(96 x temp in Kelvin) / Pressure in hPa

Front 45

What are altimeters calibrated to in order to display height?

Back 45

ISA conditions, altimeters change by 27ft (30ft) for every 1 hPA

Front 46

What is the effect of temperature on the pressure lapse rate?

Back 46

Cold air causes a faster pressure lapse rate, and warm air causes a slower pressure lapse rate.

Front 47

Why does cold air cause pressure to change more rapidly?

Back 47

Cold air is more dense, therefore there is more mass contained in the lower levels of atmosphere and more vertical pressure variation in the lower

Levels

Front 48

Above warm air the pressure is _______ than at the same level above cold air

Back 48

Higher

Front 49

If temperature is colder than ISA, the pressure lapse rate is ________ _______ than 27 ft per 1 hPa

Back 49

Less than....eg 25ft per 1hPa

Front 50

What is SPS?

Back 50

Standard Pressure Setting

1013.25 mb, MSL pressure in ISA conditions

Front 51

What is the ISA pressure lapse rate?

Back 51

27 ft per 1 hPa

Front 52

When is SPS used?

Back 52

Above the transition level, which varies according to location taking into account terrain etc

Front 53

What is QFF used for?

Back 53

Forecasting purposes and a more accurate indication of what actual MSL is

Front 54

Pressure lapse rate is ________ in colder temperatures and _________ in warmer temperatures.

Back 54

Higher in colder temperatures and lower in warmer temperatures

Front 55

Above sea level in warmer than ISA conditions would QFF value be lower or higher than QNH?

Back 55

Lower

Front 56

at an Aerodrome Above sea level in warmer than ISA conditions would QFF value be lower or higher than QNH?

Back 56

Lower

Front 57

At an aerodrome above sea level In air colder than ISA conditions, would QFF value be higher or lower than QNH?

Back 57

Higher

Front 58

For an airfield below sea level, in colder than ISA conditions, would QFF value be higher or lower than QNH?

Back 58

Lower

Front 59

What is air density?

Back 59

The measurement of the mass of air within a given volume of atmosphere

Front 60

The greater the mass of air within a given volume, the _______ the density.

Back 60

Greater

Front 61

Air density has a significant effect on aircraft _________

Back 61

Performance

Front 62

Air density is expressed as what?

Back 62

Kg/m3 or g/m3

Front 63

In ISA at MSL what is the air density?

Back 63

1.225 kg/m3 or 1225 g/m3

Front 64

As temperature increases the density of air ________.

Back 64

Increases the density of air decreases

Front 65

As temperature decreases, the density or air ________

Back 65

Increases

Front 66

Why does higher temperature cause air to become less dense?

Back 66

Heat gives air molecules greater energy and they move around more, and occupy a larger volume of space

Front 67

Why do cold temperatures cause air to become more dense?

Back 67

The air molecules lose their energy, move around less and therefore occupy less volume of space.