1. Essential Question: How does WATER in the atmosphere affect weather and climate? What is the most important gas in the atmosphere for weather? What is humidity? What does saturation mean? How do KE, temperature and evaporation relate? (Table 4.1) How do you determine the relative humidity? Problem #3 page 128 What are TWO ways to change humidity? How does Humidity change throughout the day?

2. Humidity The amount of water vapor in the air. There are several ways to express this: Absolute humidity Specific Humidity (Mixing Ratio) Vapor pressure Relative humidity Dew point

3. Mixing Ratio (specific humidity) The mass of water vapor in 1 kg of dry air 1 kg of dry air

4. Mixing Ratio varies with Temperature At 25° the air will hold _____g At -40° the air will hold ______g At 35 ° the air will hold ____g

5. Saturation When the air contains the MAXIMUM amount of water vapor that it can hold at that temperature. _______% humidity No more room between molecules, Not enough KE to keep water vapor molecules suspended in air

6. Summarize…. As the air temperature increase, the amount of water vapor in the air ________________

7. Humidity Is the RATIO of the actual amount of water vapor in air Compared to the amount of water vapor that the air can hold at that temperature and pressure. Relative humidity = mixing ratio (actual amount grams) max. capacity (saturation) Has / Hold

8. Humidity Is the measure of the Content of Water Vapor in the Air

9. Relationship between Vapor Pressure and Saturation

10. Relative Humidity At 25° C the air can hold _______g If there is 10g of actual water vapor in the air… Then the humidity is 10g = 20g % 50

11. Relative Humidity Practice At 5°C the air can hold _____g of water vapor If the air has 4 grams of water vapor in it, 4g = 5g The humidity is ________%

12. Hot desert air with low relative humidity will actually have a higher water vapor-content than frigid air with high relative humidity -10°C can ONLY hold 2g, so 1g would be 50% humidity 40°C can hold 47g, so 10% humidity = 4.7g of water vapor

13. Sling Psychrometer Compares the temperature of a dry thermometer bulb, to the temperature of a wet thermometer bulb

14. Evaporation is a cooling process Water absorbs heat energy as it evaporates. Water takes “steals” heat energy to escape from the surface. Lowering the temperature of the remaining water

16. Two ways to change humidity: 1.Add more water vapor to the air and humidity will increase Caused by Increased evaporation from the ocean 15°C 10 g/kg____% 2g 10g

17. Humidity Changes by Adding Moisture

18. Ways to add moisture transpiration

19. 2. Change the temperature. Decrease the temperature and the humidity _________. Increase the temperature and the humidity ________. 5g 20g 5g 10g 5g

20. Daily Changes in Relative Humidity with Temperature. Why is humidity the highest when the temperature is the lowest?

21. Relative Humidity: Changes with Temperature :

22. BELL WORK Table 4.1 (page 105) 1.If the air in the room currently contains 10 g of water vapor, is it SATURATED? 2.How many more grams of water would it need to be saturated? 3.What temperature would you need to cool the room to for it to be saturated?