1. Wicked Weather WHAT YOU LEARN How we measure humidity. How fog, frost, and dew form. Why and how clouds form. Adiabatic Cooling and Warming. How clouds are classified. How orographic, convectional, and cyclonic precipitation occur

2. WATER VAPOR IS THE MOST IMPORTANT ATMOSPHERIC GAS. WHY? Water vapor is the source of moisture for clouds, rain, frost, etc. Water vapor releases latent heat when it condenses. Water vapor is a heat-absorbing gas. Water vapor influences our sense of temperature.

3. WHAT IS HUMIDITY? Humidity is the amount of water vapor in the air. Specific humidity is the weight of water vapor in grams contained in a kilogram of air. Relative humidity is the ratio of the water vapor present to its potential water vapor capacity.

5. WHAT IS SATURATION? Some water molecules leave (evaporate), others return to the water. Evaporation increases Vapor Pressure of air. Eventually water molecules leaving equals the amount returning. This is saturation (filled to capacity).

6. http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/atmospheric_moisture/concept_of_saturation.htm

7. WATER VAPOR CAPACITY The air’s capacity to hold water vapor varies with temperature. Warm air can hold more water vapor than cold air. Air with a specific humidity of 7 grams/kg at 10 °C is saturated (100% RH). The same air with 7 grams/kg at 20 °C has a relative humidity of ________

8. SATURATION If air can no longer hold water vapor without condensing, it: –Is saturated. –Has a relative humidity of 100%. –Has reached its dew point temperature.

9. CONDENSATION Dew point temperature and relative humidity tell how close an air mass is to saturation. Air is saturated when the dew point temperature and the air temperature are the same.

10. MEASURING HUMIDITY Relative humidity and dew point temperatures can be determined using a sling psychrometer. The difference between the wet and dry bulb temperatures is applied to a sliding scale or published tables. http://images.usatoday.com/weather/photos/sling2.gif

11. HOW DOES DEW AND FROST FORM? Moist air in contact with a cold surface condenses into liquid water droplets. This is dew. Moist air in contact with a cold surface

12. Moist air condenses on a surface below freezing, ice crystals form. This is frost. Dew and frost occur on cool, calm, clear nights Why? Radiation cooling http://www.malawicichlidhomepage.com/macro_nature/frost01.jpg

13. WHAT IS FOG? A cloud on the ground Fog in California forms in two major ways: –Radiation cooling –Advection cooling http://www.photohome.com/pictures/sunrise-sunset-pictures/pier-trail-path-fog-1a.jpg

14. RADIATION FOG Radiation to space on cold, calm, clear nights chills a deep layer of air below dew point. Water vapor condenses onto condensation nuclei. Tiny water droplets form radiation fog. http://www.rjma.com/flight/airwaves/PH02068J.jpg

15. WHY AND HOW CLOUDS FORM? Three things are required for clouds to form: –Water vapor in the air. –Condensation nuclei. –A cooling process. Adiabatic cooling forms clouds

16. THE ADIABATIC PROCESS Adiabatic temperature change is cooling or warming caused by expansion or compression of a gas. No heat is added or subtracted. http://www.kidsgeo.com/images/adiabatic.jpg

17. HOW ARE CLOUDS CLASSIFIED? Clouds are classified by height and shape http://www.enchantedlearning.com/cgifs/clouds.GIF

18. PRECIPITATION Not all clouds produce precipitation. For precipitation large masses of air must be forced upward and cooled adiabatically. http://imagecache2.allposters.com/images/pic/IMCcard/KD6061~Raining-Cats-Dogs-Posters.jpg

19. LIFTING MECHANISMS Orographic lifting - Moist air is lifted over mountain barriers http://upload.wikimedia.org/wikipedia/commons/thumb/b/b2/Orographic_lifting_of_the_air_-_NOAA.jpg/800px-Orographic_lifting_of_the_air_-_NOAA.jpg

20. Convectional lifting - Unequal heating produces a rising current of air. http://geography-info.com/physical/images/6/convectional.gif

21. Cyclonic or Frontal lifting - Warm air rises in contact with a cold air mass. http://upload.wikimedia.org/wikipedia/commons/thumb/0/03/Cyclone_Larry_2006.jpg/600px-Cyclone_Larry_2006.jpg

22. Convergence - Air flows together http://bimedia.ftp.clickability.com/wshmwebftp/WebStuff/Convergence_Divergence.jpg

23. CONVERGENCE LIFTING Air masses converge. Air forced upwards. Common near Equator at Intertropical Convergence Zone (ITCZ). : http://ww2010.atmos.uiuc.edu/guides/mtr/cld/dvlp/gifs/cnvrg1.gif

24. LIGHTNING Lightning is associated with convectional lifting and cumulonimbus clouds. Rapid updrafts and downdrafts generate electricity which is discharged as thunder and lightning. http://www.starstore.com/acatalog/lightning-bolt-poster.jpg

25. cited College of Alameda Physical Geography,2004, Moisture in the Atmosphere Learning Module (internet).Moisture in the Atmosphere Learning Module All photos cited on powerpoint.