Humidity, Saturation, and Stability: Part 1

Question 1

What does the saturation vapor mixing ratio of air depend on?

Answer 1

Pressure and temperature

Question 2

What happens to the humidity and vapor mixing ratio of a saturated air parcel as its temperature falls?

Answer 2

Humidity does not change and the vapor mixing ratio decreases

Question 3

What happens to the density and relative humidity of an unsaturated air parcel as its temperature and pressure do not change and its vapor mixing ratio increases?

Answer 3

Density decreases and relative humidity increases

Question 4

If the vapor mixing ratio of a parcel of air is 2g/kg and its saturation mixing ratio is 6g/kg. What is its relative humidity?

Answer 4

33.3%

Question 5

If the mixing ratio of a parcel of air is 6g/kg and the relative humidity is 25%. What is the saturation mixing ratio?

Answer 5

24g/kg

Question 6

If the air is 12°C and the vapor mixing ratio is the same as the saturation vapor mixing ratio. Is the dewpoint temperature less than, equal to, or more than the temperature?

Answer 6

It is equal to the temperature

Question 7

On a clear and calm day, what usually happens to the relative humidity between sunrise and early afternoon?

Answer 7

It falls

Question 8

What soundings always indicate stable atmosphere conditions?

Answer 8

Temperature inversion, isothermal conditions, and either no change or an increase in temperature with altitude

Question 9

What does conditional instability indicate in an air layer?

Answer 9

That it is unstable for saturated and stable for unsaturated air parcels

Question 10

How does unstable air affect the vertical motion of air parcels?

Answer 10

It enhances it.

Question 11

Why don’t rising parcels of saturated air not cool as rapidly as rising parcels of unsaturated air?

Answer 11

Because expansion cooling of saturated air is partially compensated for by the release of latent heat

Question 12

What happens to the saturation mixing ratio as saturated air flows up the windward slopes of a mountain range?

Answer 12

It decreases

Question 13

What happens when unsaturated air flows down the leeward slopes of a mountain range?

Answer 13

• Air temperature rises
• Relative humidity decreases
• Saturation vapor pressure increase

Question 14

What happens when a clear parcel of air ascends dry adiabatically?

Answer 14

• Its relative humidity increases
• Its saturation vapor mixing ratio decreases
• Its temperature drops

Question 15

Suppose the vapor mixing ratio of the cold outside air is the same as the vapor mixing ratio of the warm air indoors. What happens to the relative humidity indoors if the door was opened and the cold air replaces some of the warm air.

Answer 15

It becomes higher than before

Question 16

Which pair of processes, working together, will make the atmosphere more unstable?

Answer 16

Warm the surface and cool the air aloft

Question 17

A parcel of unsaturated air descends adiabatically without mixing. What happens to the temperature when it descends 800m?

Answer 17

It warms 8°C

Question 18

What does 10% relative humidity mean?

Answer 18

10% of the mass of air consists of water vapor

Question 19

Consider the case of very calm wind conditions near the ground. What happens to the relative humidity when the air temperature increases?

Answer 19

It decreases

Question 20

What happens to the temperature of an air parcel when it rises without mixing with ambient air?

Answer 20

It decreases

Question 21

What is vapor pressure?

Answer 21

The partial pressure exerted by water vapor alone

Question 22

What is the mixing ratio?

Answer 22

The mass of vapor divided by the mass of dry air

Question 23

What is humidity?

Answer 23

The amount of water vapor

Question 24

What does saturation vapor pressure depend on?

Answer 24

Temperature

Question 25

What is isobaric cooling?

Answer 25

When a system cools while the pressure remains constant

Question 26

What is isothermal compression?

Answer 26

When pressure increases while the temperature remains constant

Question 27

What is relative humidity?

Answer 27

The vapor pressure divided by saturation vapor pressure

-i.e. the amount of water vapor in the air vs the amount the air can hold

Question 28

What happens when unsaturated air cools?

Answer 28

• Vapor pressure does not change
• Temperature decreases
• Saturation vapor pressure decreases
• Relative humidity increases

Question 29

What happens when unsaturated air warms?

Answer 29

• Vapor pressure does not change
• Temperature increases
• Saturation vapor pressure increases
• Relative humidity decreases

Question 30

What is a dewpoint?

Answer 30

The temperature at which air must be cooled at a constant pressure to reach saturation.

Question 31

How can dewpoint be used?

Answer 31

Relative humidity = saturated vapor pressure at dewpoint / saturated vapor pressure at a temperature

Question 32

What is the mixing ratio?

Answer 32

The mass of water vapor contained in 1kg of dry air

Question 33

What is the saturated mixing ratio?

Answer 33

The max amount of water vapor 1kg of dry air can contain

Question 34

What does saturated mixing ratio depend on?

Answer 34

Temperature and pressure

Question 35

How can you calculate relative humidity with the mixing ratio and saturated mixing ratio?

Answer 35

Relative humidity = mixing ratio / saturated mixing ratio

Question 36

What is precipitable water?

Answer 36

The amount of water content of a vertical column of air from the surface to the top of the atmosphere

Question 37

How much water would be produced if you condensed all water vapor in the atmosphere?

Answer 37

2.5cm deep pool of water globally