1. Water in the Atmosphere

2. Water exists in the atmosphere as:
Gas  water vapor
Solid  ice crystals
Liquid  water droplets

3. Changing States Solid to liquid: Melting Liquid to solid: Freezing
Ice absorbs heat and turns
to liquid
Liquid to solid: Freezing
Water loses heat, and turns to ice

4. Liquid to Gas: Evaporation
Gas to liquid:
Condensation
Heat is released
into surroundings
Liquid to Gas: Evaporation
Heat is absorbed from surrounding

5. Gas to solid: Deposition
Solid to gas:
Sublimation
Heat absorbed
Gas to solid: Deposition
Heat released

6. Humidity
The amount of water vapor in the atmosphere is called humidity.
Air that has reached its water vapor capacity is said to be saturated
Humidity depends on temperature since different temperatures have different saturation points

7. Relative Humidity
Relative Humidity is the amount of water in the atmosphere compared to how much water the air can hold
Indicates how near the air is to saturation
Actual Moisture X 100 = Relative Humidity
Maximum Moisture

8. Hot Air vs. Cold Air
The warmer the air the more water vapor it can hold
By changing the temperature of the air you can increase or decrease the relative humidity
Constant water vapor and higher temp = lower RH
Constant water vapor and lower temp = higher RH

9. Warm, saturated air contains more water vapor than cold saturated air

10. Specific Humidity Number of grams of water vapor in 1 kg of air (g/kg)
Actual amount of water vapor in air
Hot, summer day in NC--> 20 g/kg
Cold, winter day in NC--> 5 g/kg

11. Measuring Humidity Measured with hygrometer
One type of hygrometer is called a psychrometer
Made of two thermometers- 1 dry, 1 wet
Dry thermometer = air temperature
Wet thermometer = as water evaporates it removes energy from thermometer, lowering the temperature
Compare both thermometers in table to find RH
Ex. In cloud no evaporation because air already saturated.

12. Sling Psychrometer
and RH Table
Smaller differences between wet and dry = higher RH
Larger differences between wet and dry = lower RH

13. Hair Hygrometer
Instrument that records the changing length of hairs when humidity changes
Human hair stretches when humidity increases

15. Heat Index Determines what the air temperature ‘feels’ like.
High air temp + low RH = air temp feels lower than it really is
High air temp + high RH = air temp feels higher than it really is

16. Dew Point
Dew point – temperature to which air must be cooled to reach saturation
If the temperature drops to the dew point then the moisture in the air will begin to condense and form dew (> 0 C) or frost (< 0 C)
If humidity is high, a small temperature drop will reach dew point.
If humidity is low, a large temperature drop will reach dew point.