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

18. Humidity
Vapor Pressure in mb is the fraction of the total air pressure coming from the molecular movement of water vapor molecules.
Normal sea level pressure is around 1000 mb
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

19. Humidity Other measures that are used. Mass of water vapor
volume of air
Absolute humidity =
g/m3
Mass of water vapor
total mass of air
Specific humidity =
g/kg
Mass of water vapor
mass of dry air
Mixing ratio =
g/kg

21. Mt. Hood
Mt. Rainer

23. Relative Humidity

26. Dew point Temperature (directly linked to actual humidity)
Temperature that results in saturation or
dew forming on surfaces.
High dew point high actual humidity
Low dew point low actual humidity
Dew points in excess of 70 F will normally make one uncomfortable.

28. Outside
T = -15 C
Td = -15 C
RH =100%
Inside
T = 20 C
Td = -15 C
RH = 8%

32. Hygrometers measure humidity
A Sling Psychrometer is common