Physical GeographyClass 21: Humidity

A measure of how much water vapor is in the air

What is humidity?

What is the source(s) of water vapor?

20%

60%

0%

0%

0%

0%

20%

0% 1. Transpiration2. Evaporation3. Deposition4. Sublimation5. Condensation6. 1, 2 and 37. 2, 3 and 58. 1, 2 and 4

What happens if wind increases?

0%

20%

20%

40%

20% 1. Condensation increases2. Evaporation increases3. Condensation + evaporation

increase4. Evaporation decreases5. Both condensation and evaporation

decrease

Air with high levels of water vapor:

60%

0%

20%

20%

0% 1. Will lead to high rates of evaporation

2. Will lead to low rates of evaporation3. May lead to condensation4. 1 and 25. 2 and 3

Actual amount of water vapor◦ Absolute Humidity◦ Specific Humidity◦ Vapor Pressure◦ Dew Point

Different ways to express humidity

Mass of water vapor/volume of air

Units: grams/cubic meter

Maximum potential absolute humidity related to temperature

Temperature increase = increase in potential maximum

Absolute Humidity

Mass of water vapor per mass of air

Grams of water vapor/kilograms of air

Specific Humidity

The portion of air pressure that comes from water vapor

Units: same as air pressure (millibars)

Saturation vapor pressure = maximum possible

Above saturation condensation

Vapor Pressure

Sat. V.P increases with temp.

Temperature and Relative Humidity

As water vapor in air cools, what phase change is likely to occur?

1. Evaporation2. Transpiration3. Condensation

What are two ways that maximum water vapor can be reached?

1. Add more moisture and lower temperature

2. Remove water vapor and lower temperature

3. Add more moisture and raise temp4. Remove water vapor and raise

temp

If the absolute humidity stays same, what will happen as temp increases?

1. Relative humidity will increase2. Relative humidity will stay same3. Relative humidity will decrease

Which has the potential to contain more water vapor?

1. Warm air2. Cold air

As air cools, maximum water vapor can be reached.

Dew Pt temperature = temp. at which this occurs

100% Relative Humidity or Saturation

Dew Point/CondensationTemperature

Dew point is a way of measuring:

1. The actual amount of water vapor in the air

2. The relative humidity

A high dew point means

1. A high amount of water vapor2. A low amount of water vapor3. A high relative humidity4. A low relative humidity

How can saturation be reached?

0%

0%

0%

0%

0%

0%

0%

0% 1. By evaporation of more water2. By condensation of more water3. By lowering temperature4. By raising temperature5. 1 and 36. 2 and 47. 1 and 48. 2 and 3

Hot and dry vs. hot and humid (heat index)

Cold and humid vs. cold and dry

Wind chill

Human Comfort and Humidity