1. Water in the Atmosphere
Water is introduced into the atmosphere through evaporation
Humidity
The amount of water vapor in the air varies depending on air temperature and moisture
SPECIFIC HUMIDITY: The actual amount of water vapor in the air.
Depends on air temp.
Warm air holds more vapor than cool air
When the air has a maximum amount of water vapor it can hold, it is said to be saturated.
Saturation is when actual vapor density=saturation vapor density

2. Water in the Atmosphere
Air with higher temperatures can hold more water vapor than air at lower temperatures.
Relative Humidity: How near the air is to saturation.
Looks at actual vapor density in relation to saturation vapor density for air at a given temperature.
@ 10 C a cubic meter of air holds at most 8 grams of water vapor
If there were 8 grams in the air R.H. = 100%
If there were 4 grams in the air R.H. = 50%

3. Water in the Atmosphere
Measuring Humidity
Air temperature is measured with a dry-bulb thermometer
Wet bulb thermometer uses evaporation as a cooling process.
Drier air has higher rates of evaporation, which causes a lower wet-bulb temperature.
More moist air has lower rates of evaporation, which causes a higher wet-bulb temperature.
Difference between dry-bulb temperature and wet-bulb temperature can give relative humidity.

4. Water in the Atmosphere
Humidity and Condensation
Condensation occurs when air becomes cooler.
Temperature at which condensation occurs for a given humidity is known as dew point.
Ex.: Wet grass in the morning

5. Water in the Atmosphere
Measuring Relative Humidity
Psychrometer
Has a wet-bulb and dry-bulb thermometer
The bulb of the wet-bulb thermometer has a cloth covering moistened in water
When slung air blows over both thermometers
The wet-bulb thermometer is cooled by evaporation and the reading drops below the dry-bulb thermometer reading
The relative humidity can be found by comparing the temperatures of the wet-bulb and dry-bulb thermometers

6. Water in the Atmosphere