Pressure System

Question 1

What causes atmospheric pressure at any point?

Answer 1

The weight of the overlying air.

Question 2

What unit is commonly used in aviation to measure atmospheric pressure?

Answer 2

Hectopascal (hPa).

Question 3

What older unit is equivalent to 1 hPa?

Answer 3

1 millibar (mb).

Question 4

How much pressure is 29.92 inHg equivalent to in hPa?

Answer 4

1013.2 hPa.

Question 5

What is the SI metric equivalent of 1 kilopascal (kPa)?

Answer 5

10 hectopascals (hPa).

Question 6

How does a mercury barometer work?

Answer 6

Atmospheric pressure pushes mercury up a tube; the height reflects the pressure.

Question 7

What is station pressure?

Answer 7

The atmospheric pressure at the elevation of the observing station.

Question 8

What is mean sea level pressure (MSL)?

Answer 8

Station pressure adjusted to sea level using temperature and standard lapse rate.

Question 9

Why is MSL pressure important?

Answer 9

It provides a consistent reference for comparing pressure across different elevations.

Question 10

What is the altimeter setting?

Answer 10

The MSL pressure adjusted using standard conditions to make the altimeter read the true airport elevation.

Question 11

What are isobars?

Answer 11

Lines on a map connecting points of equal pressure.

Question 12

At what interval are isobars typically drawn?

Answer 12

Every 4 hPa.

Question 13

What do concentric isobars around a low indicate?

Answer 13

A depression or low-pressure system.

Question 14

What does a high-pressure area look like on a weather map?

Answer 14

Concentric isobars with the highest pressure at the center.

Question 15

What are the main types of pressure systems?

Answer 15

Lows, secondary lows, troughs, highs, ridges, and cols.

Question 16

What is a low-pressure area also called?

Answer 16

Cyclone or depression.

Question 17

What weather is associated with a low?

Answer 17

Rainy, cloudy, and unsettled weather.

Question 18

How fast do lows typically move in winter?

Answer 18

About 700 miles (1,100 km) per day.

Question 19

What is a secondary low?

Answer 19

A smaller low-pressure system rotating around a main depression.

Question 20

What is a trough of low pressure?

Answer 20

An elongated area of low pressure with higher pressure on both sides.

Question 21

What is another name for a high-pressure system?

Answer 21

Anticyclone.

Question 22

What weather is typical in a high?

Answer 22

Fair, clear, and calm weather.

Question 23

What direction do winds circulate around a high in the Northern Hemisphere?

Answer 23

Clockwise and outward.

Question 24

What is a ridge?

Answer 24

A narrow area of high pressure extending from a high.

Question 25

What is a col?

Answer 25

A neutral area between two highs and two lows; typically unstable.

Question 26

What is the pressure gradient?

Answer 26

The rate of change in pressure over a given distance.

Question 27

What indicates a steep pressure gradient on a weather map?

Answer 27

Closely spaced isobars.

Question 28

What does a steep pressure gradient mean for wind speed?

Answer 28

Stronger winds.

Question 29

What does a shallow pressure gradient mean?

Answer 29

Light winds.

Question 30

What direction is the pressure gradient measured?

Answer 30

At right angles to isobars.

Question 31

What is the Coriolis force?

Answer 31

A deflecting force due to Earth’s rotation.

Question 32

Which direction does the Coriolis force deflect wind in the Northern Hemisphere?

Answer 32

To the right.

Question 33

What is Ferrel’s Law?

Answer 33

Moving air appears deflected right in the Northern Hemisphere and left in the Southern Hemisphere.

Question 34

What direction do winds blow around a low in the Northern Hemisphere?

Answer 34

Counterclockwise and inward.

Question 35

What direction do winds blow around a high in the Northern Hemisphere?

Answer 35

Clockwise and outward.

Question 36

What effect does surface friction have on wind?

Answer 36

Slows it down and reduces Coriolis deflection.

Question 37

How much can surface friction deflect wind over land?

Answer 37

Up to 40° inward toward a low.

Question 38

How much is the typical wind deflection over water?

Answer 38

Less than 10°.

Question 39

Up to what altitude can surface friction affect wind?

Answer 39

About 2,000 feet.

Question 40

What happens to wind direction above the friction layer?

Answer 40

Winds flow parallel to isobars.

Question 41

What is centrifugal force in meteorology?

Answer 41

The outward force acting on rotating air masses.

Question 42

What does centrifugal force do to wind speed in highs?

Answer 42

Increases it.

Question 43

What does centrifugal force do to wind speed in lows?

Answer 43

Decreases it.

Question 44

How often are pressure readings taken at weather stations?

Answer 44

Hourly.

Question 45

How often are weather maps prepared?

Answer 45

Every 6 hours (4 times per day).

Question 46

What is pressure tendency?

Answer 46

The pattern of pressure change over time.

Question 47

What does falling pressure usually indicate?

Answer 47

An approaching low-pressure system.

Question 48

What does rising pressure indicate after a low passes?

Answer 48

Improving weather.

Question 49

What is convergence?

Answer 49

Air flowing into a region, often causing rising motion and precipitation.

Question 50

What is divergence?

Answer 50

Air flowing out of a region, often causing sinking motion and clear weather.