http://www.chm.davidson.edu/ronutt/che115/Phase/Phase.htm

http://ga.water.usgs.gov/edu/watercycle.html

Figure 2. The mean distribution of precipitable water, or total atmospheric water vapor above the Earth's surface, for 1992. This depiction includes data from both satellite and radiosondeobservations. (Image courtesy of Thomas Vonder Haar and David Randel, Colorado State University, Fort Collins.)

Humidity

Normal sea level pressure is around 1000 mb

Vapor Pressure in mb is the fraction of the total air pressure coming from the molecular movement of water vapor molecules.

So a vapor pressure of 10 mb means that 1% of all air is water vapor.

20 mb 2%

40 mb _______ %

An actual humidity of 10 mb means that 1 % of all air molecules are water vapor

A saturation humidity of 10 mb means that at most 1 % of all air molecules Can be water vapor

Humidity

Absolute humidity = Mass of water vapor volume of air

Specific humidity = Mass of water vapor total mass of air

Mixing ratio = Mass of water vapor mass of dry air

Other measures that are used.

g/m3

g/kg

g/kg

Saturation Vapor Pressure vs Temperature

500

600

700

800

900

1000

80 90 100 110

Temperature (°C)

Mt. Hood

Mt. Rainer

Relative Humidity

RH Actual _ Humidity

Saturation _Humidity

Saturation Vapor Pressure (mb) vs Temp. C

0

5

10

15

20

25

30

35

40

-10 0 10 20 30

Temperature (°C)

A

B

Dew point Temperature(directly linked to actual humidity)

Temperature that results in saturation or dew forming on surfaces.

High dew point high actual humidityLow dew point low actual humidity

Dew points in excess of 70 F will normally make one uncomfortable.

Outside

T = -15 CTd = -15 CRH =100%

Inside

T = 20 CTd = -15 CRH = 8%

Hygrometers measure humidity

A Sling Psychrometer is common