Climate Lecture 3- Water in the Atmosphere

Question 1

How much water is in the atmosphere?

Answer 1

12,900 km3
This is 0.001% of Earth’s total water volume

Question 2

If all the water in the atmosphere rained down at once how much depth would it cover the globe?

Answer 2

2.5 cm
This amount is referred to as precipitable water.

Question 3

When is latent heat absorbed?

Answer 3

Energy consuming processes (cooling) such as evaporation or melting or sublimation.

Question 4

When is latent heat released?

Answer 4

Freezing, condensation or deposition

Question 5

How many MJ in sublimation?

Answer 5

2.83 MJ/Kg

Question 6

How many MJ in latent heat of vaporisation or condensation?

Answer 6

2.5 MJ/Kg

Question 7

How many MJ in latent heat of fusion (melting)?

Answer 7

0.33 MJ/Kg

Question 8

What is mixing ratio?

Answer 8

G/Kg
Weight of water vapour per unit weight of dry air

Question 9

What is absolute humidity?

Answer 9

g/m3
The weight of water vapour per unit volume of air

Question 10

What is relative humidity measured as?

Answer 10

%

Question 11

What is vapour pressure measured as?

Answer 11

hPa

Question 12

What happens if evaporation = condensation?

Answer 12

A state of saturation is reached.

Question 13

What happens to saturation mixing ratio ad temperature increases?

Answer 13

Increases

Question 14

What happens to relative humidity as temperature increases?

Answer 14

Decreases
E.g. 10 degrees = 100%, 20 degrees = 52% and 30 degrees = 28%

Question 15

What is transpiration?

Answer 15

Process by which plants lose water through stomata

Question 16

What is AET?

Answer 16

Actual evapotranspiration
The amount actuallt evaporated

Question 17

What is PET?

Answer 17

Potential evapotranspiration
Amount that would be evaporated if there was no limit of water availability

Question 18

What is PET often referred to as?

Answer 18

Climatic demand

Question 19

Is radiation a determinant of atmospheric moisture levels?

Answer 19

Yes

Question 20

Discuss energy consumption in evaporation in January (latent heat).

Answer 20

High in areas with warm ocean currents, equatorial/tropical forests and areas of high pressure.

Question 21

Discuss energy consumption in evaporation in July (latent heat).

Answer 21

High in areas with summer vegetation growth.

Question 22

Discuss the role of humidity gradient.

Answer 22

If there is high evaporation - steep moisture gradient between saturated surface (high humidity) and dry atmosphere (low humidity)

If there is low/no evaporation- little or no moisture gradient between saturated surface (high humidity) and saturated atmosphere (high humdity)

Question 23

Discuss the role of wind (turbulence)

Answer 23

High evaporation- if there is a saturated surface (high humifity) and saturated atmosphere (high humidity) with strong wind/turbulence then moisture is carried away and so atmospheric humidity is lowered and humidity gradient is restored.

Low/no evaporation- if there is a saturated surface (high humifity) and saturated atmosphere (high humidity) with weak wind/turbulence then moisture is not carried away and so there is weak or no humidity gradient remaining.

Question 24

What are lapse rates?

Answer 24

Rate of change in temperature with height through the lower layers of the atmosphere

Question 25

What are the two broad types of lapse rate?

Answer 25

Environmental and Adiabatic

Question 26

What is environmental LR?

Answer 26

This is the expected decrease in temperature with height through the lower atmosphere, approximately 6.5oC/km.

Question 27

What is adiabatic LR?

Answer 27

Used to explain what occurs as a parcel of air rises, decreases in pressure and temperature, but increases in volume. The conditions are reversed if a parcel of air moves towards Earth. Can either be dry or saturated.

Question 28

Discuss dry adiabatic lapse rate (DALR).

Answer 28

Dry adiabatic lapse rate (DALR): This is the rate a parcel of air cools at as it rises (or warms if falling) if condensation does not occur. The rate is approximately 1 degree per 100m (10oC/km)

Question 29

Discuss saturated (moist) adiabatic lapse rate (SALR/MALR).

Answer 29

The rate at which air cools if condensation occurs. The rate of cooling is slower than the DALR because of the release of latent heat. The SALR/MALR varies from 4 – 9oC/km, but the global average is ~6.0oC/km

Question 30

What happens with dry adiabatic lapse rate?

Answer 30

High air pressure near surface and lower air pressure higher. Rising air expands and cools and so temp decreases. Sinking air parcel is compressed and warms so temp increases

Question 31

How can atmospheric stability be assessed?

Answer 31

Need to know relationship between the temperature of a parcel of air (Tp) and that of the surrounding air (the environment) (Te) at any given altitude

Question 32

Discuss atmospheric stability in terms of Tp and Te.

Answer 32

– if Tp > Te then parcel of air is lighter than its environment and it will rise – if Tp = Te then parcel of air remains stable (not rise or sink) – if Tp < Te then parcel of air is heavier (denser) than its surrounds and will sink

Question 33

Discuss environmental stability in terms of lapse rate.

Answer 33

Absolute stability occurs when... Γd > Γs > Γe Γd is the dry adiabatic lapse rate (10°C/km) Γs is the saturated adiabatic lapse rate (6°C/km) Γe is the environmental lapse rate (actual rate of T decrease)

Question 34

What is the condition for absolute atmospheric instability?

Answer 34

Γe> Γd> Γs Hence, an unsaturated or saturated parcel will always be warmer (Tp >Te) than the environment and will continue to ascend.

Question 35

What determined that stability for rising parcels of air?

Answer 35

Environmental temperatures

Question 36

When does condensation occur?

Answer 36

When the dew-point temperature is reached

Question 37

What is dewpoint?

Answer 37

Temperature at which saturatiom occurs

Question 38

What is condensation?

Answer 38

Direct cause of all precipitation

Question 39

What causes condensation?

Answer 39

1. Air mass mixing (eg warm/cool air mixing)  Vertical  Horizontal 2. Increased water content (eg evaporation) 3. Dynamic (adiabatic) Cooling  Cooling/warming due to expansion/compression  no heat added or subtracted

Question 40

What are four key uplift causes?

Answer 40

 Convective lifting (eg thunderstorms)  Orographic lifting (eg over mountains)  Frontal wedging (eg contrasting air masses meeting)  Convergence (eg bumping of two opposing streams of air)

Question 41

What is an occluded front?

Answer 41

An occlusion occurs when the cold front 'catches up' with the warm front.

Question 42

Where is strongest effective precipitation?

Answer 42

Equator This drops in the topical regions

Question 43

Where is soil moisture greatest?

Answer 43

Closer to the poles

Question 44

Where is runoff greatest?

Answer 44

Closer to the poles (Europe/Canada etc)

Question 45

Name 5 things which determine evaporation.

Answer 45

Temperature Radiation Vertical humidity Gradients Wind speed

Question 46

What do global patterns of moisture largely reflect?

Answer 46

Distribution of latent heat flux and atmospheric circulation pattern

Question 47

What are large seasonal variations in atmospheric moisture due to?

Answer 47

Changes in energy supply and the global atmospheric circulation