1. Atmospheric Moisture

2. How does the moisture get in the atmosphere?? EVAPORATION TRANSPIRATION – water evaporated from trees

3. Factors that affect evaporation rates (adding water vapor to the atmosphere) 1.Temperature – warmer the temperature, evaporation increases 2.Surface Area – As surface area increase, the rate of evaporation increases 3.Relative Humidity – as relative humidity increases, the rate of evaporation decreases

4. Which will evaporate faster? 4. Surface area – more surface area of water available, the more evaporation

5. ABSOLUTE HUMIDITY Amount of Water Vapor in the atmosphere Air that is full of water vapor is said to be saturated The higher the temperature, the greater the capacity of the air can “hold” water SO, As the air temperature increases, the air can hold (less or more) water

6. Relative Humidity (RH) Percentage of air that is saturated at a given temperature 50% RH = air has ½ the water vapor needed to saturate the air RH = 100% means Air is saturated, it cannot add any more water vapor or condensation will occur

7. Dew Point Temperature at which condensation occurs It’s a direct measure of the moisture content in the air. Therefore, as the dew point temp increases the amount of moisture in the air increases Air Temp = Dew Point, then RH= 100%, which equals and occurs

8. As air temperature and dew point get closer together, the probability of clouds and precipitation increases

9. Relationships A. If the moisture content remains the same: As temperature increases, RH As temperature decreases, RH decreases Indirect relationship increases Indirect relationship

10. Measuring Dew Point Instrument: Psychrometer has 2 thermometers, - dry bulb – - Wet Bulb – a piece of moist cloth wrapped around the bulb Sling Psychrometer Air temperature

11. Psychrometer The psychrometer is swung around, the wet bulb temperature drops because of the cooling effect when being Wet bulb depression - difference between the dry and wet bulbs evaporated ESRT Page 12

13. To Find Dew Point (see ESRT p. 12) Find the wet bulb depression along the top of the chart Find the air temperature along the left side of the chart Where the two meet is the dew point (You may have to estimate) Ex: Dry bulb = 20°C Wet bulb = 17°C Difference between Wet bulb and Dry Bulb = Dew point = 3°C

14. Dew Point = 15 o C

15. Dry Bulb = 11 o C Wet Bulb = 4 o C Difference between wet bulb and dry bulb = ______ Dew Point = __________ 7 o C -7 o C

16. To Find the Relative Humidity ESRT Page 12 Same procedure as finding the dew point

18. Dry Bulb = 20 o C Wet Bulb = 17 o C Difference between wet and dry bulbs = ________ oC 3

19. RH = 74%

20. Dry Bulb = 11 o C Wet Bulb = 4 o C Difference between wet and dry bulbs = ________ oC RH = _______ 7 26%