1. Atmospheric Moisture: Humidity
Earth Science
Mr. Cloud

2. Absolute v. Relative Humidity
Absolute Humidity: the actual amount of water vapor in the air
i.e. 25 g/ml
**Relative Humidity: Is the ratio of the amount of water vapor in the air to the maximum amount it can hold.
Expressed as a percent

3. How do we measure Relative Humidity?
The ‘tool’ or ‘instrument’ that measures relative humidity is called a psychrometer
Sling Psychrometer

4. Anatomy of a Sling Psychrometer
Dry-bulb: the dry-bulb is an ordinary thermometer that reads the actual temperature of the air
Wet-bulb: the wet-bulb contains a wick around its bulb
Wet-Bulb Depression: the difference between the wet and dry bulb temperatures
Let’s figure out the relative humidity of the classroom!

5. Finding Relative Humidity
The wick is wet and the instrument is then whirled in the air
The temperature of the wet-bulb drops due to the cooling effect of evaporation
To find the relative humidity we must find the difference between the wet and dry-bulb temperatures, then go to the chart!!!

6. Dew Point The temperature at which the air is filled with water vapor
If the air temperature drops below the Dew Point, water vapor in the air will condense to liquid water or sublimate to a solid
The amount of water vapor in the air directly affects the dew point.

7. Cloud Formation In order for a cloud to form, air must rise.
As air rises, it cools.
When temperature decreases, the air’s capacity to hold water vapor decreases
The air reaches the dew point, causing water vapor to condense, forming a cloud.

8. Types of Clouds

9. Cumulus Clouds

10. Altocumulus Clouds

11. Cumulonimbus Clouds

12. Stratus Clouds

13. Cirrus Clouds

14. Determining Cloud Base Altitude
Goals:
1. Determine the dry bulb and wet bulb temperatures of the air outside.
2. As a group, determine dew point temperature and cloud base altitude.
3. Formulate the step-by-step process of determining cloud base altitude.