22. Humidity

[MEASURES OF] HUMIDITY J.T. II Olivar, MAEd Faculty of Arts and Letters University of Santo Tomas

Outline of the Lecture  Absolute, Specific, and Relative Humidity  Dew Point Temperature

Absolute Humidity  A direct measure of water vapour content

of air.  Normally expressed in grams of vapour per cubic meter of air. 

g/m3

Specific Humidity  The mass of water vapour in a

given mass

of air.  Usually expressed in grams of vapour per kilogram of air. 

g/kg

Relative Humidity  The amount of water vapour in the air at a

given temperature compared with the amount that could be there. 

Actual/Capacity

 In essence, relative humidity is the

percentage of saturation.

Dew point  The temperature at which saturation is

reached.

Adiabatic Processes  Clouds form

when warm moist air rises. The process of adiabatic cooling accompanies this. As the air cools, it looses its capacity to hold moisture and condensation in the form of clouds appears.

Dry adiabatic process  As a parcel of unsaturated air rises, it

cools at the relatively steady state of 5.5 degrees Fahrenheit per 1000 feet (10 degrees Celsius per kilometre)  Lifting Condensation Level (LCL)

Wet adiabatic lapse rate  Averages about 3.3. degrees Fahrenheit

per 1000 feet (5 degrees Celsius per kilometre)

 Dry adiabatic lapse rate 

10°C per 1000 meters

 Wet adiabatic lapse rate 

5°C per 1000 meters

 Normal lapse rate 

6°C per 1000 meters