2. Weather Earth’s Changing Atmosphere

3. I. What is Weather? A. Atmosphere Weather = day to day changes in the atmosphere – layer of gases surrounding Earth - composed of 5 layers which are separated by differences in temperature

4. What is Weather? 1. Troposphere - where all weather occurs - where life is found - layer closest to Earth’s surface - as altitude increase in the troposphere, air temperature decreases

5. What is Weather? 2. Stratosphere - where jet airplanes fly – clear skies - where the ozone layer is found - ozone layer blocks harmful ultraviolet rays - ozone layer was depleted by the production and use of CFC’s (chlorofluorocarbons)

6. What is Weather? - CFC’s were used as propellants in hair spray, spray paint, etc. and as refrigerants - CFC’s in the atmosphere inhibited the formation of new ozone - holes in the ozone layer formed over the south and north poles

7. What is Weather? - since CFC’s were banned in the mid 1980s. new ozone formation has increased and the holes are beginning to close - as altitude in the stratosphere increases, temperature increases due to heating from the absorption of ultraviolet radiation by the ozone layer

8. What is Weather? 3. Mesosphere as altitude increases, temperature decreases - where the ionosphere is found – layer of charged particles (ions) that influence how radio waves travel above Earth’s surface

9. What is Weather? d. Thermosphere - as altitude increases, temperature increases - temperature increase is caused by the absorption of harmful gamma radiation - atmosphere is very thin in the thermosphere (few molecules are floating around) - those few molecules have a lot of energy, but they are few and far between

10. What is Weather? 5. Exosphere - boundary between Earth’s atmosphere and outer space 6. Composition of the Atmosphere - composed of a mixture of gases (air) - 78 % Nitrogen (N 2 ) - 21 % Oxygen (O 2 ) - 1 % Carbon dioxide (CO 2 ), Argon (Ar) and other gases

11. What is Weather? B. The Water Cycle - weather is most effected by the amount of water in the air - describes the movement of water from the hydrosphere (all the water on Earth) to the geosphere ( the solid part of Earth) and the atmosphere (all of the gases surrounding Earth)

12. What is Weather? - uses the processes of 1. precipitation - water falling out of the atmosphere 2. evaporation - change of liquid water to gaseous water vapor 3. transpiration - loss of water from the leaves of plants (evapotranspiration)

13. What is Weather? 4. runoff - liquid water flowing over the solid surface of Earth 5. infiltration - movement of water into the ground

14. What is Weather? C. Humidity, Relative Humidity, Holding Capacity, and Dewpoint 1. Humidity - how much water is in the air 2. Holding capacity - how much water air at a specific temperature can hold

15. What is Weather? - holding capacity increases as air temperature increases - holding capacity decreases as air temperature decreases

16. What is Weather? 3. Relative Humidity - value determined by comparing humidity to holding capacity - expressed as a percentage (%) - determined using a sling psychrometer

17. What is Weather? a. Calculating Relative Humidity 1. Take the difference between the wet and dry bulb temperatures 2. Find the dry bulb temperature on the left hand side of the chart. 3. Read across to the column with the same value as the difference between the wet and dry bulb temperatures 4. The value found in the corresponding box is the relative humidity

18. What is Weather? 4. Dewpoint - temperature at which water in air condenses into a liquid - varies depending upon air temperature - expressed as a temperature in °C or °F - when air temperature reaches the dewpoint, precipitation may occur if there is enough water in the air

19. What is Weather? - depends upon holding capacity - precipitation can occur when the air temperature is warmer than the dewpoint because there is so much water in the air

20. What is Weather? D. Clouds and Precipitation 1. Clouds - when water in the air begins to condense, it may form clouds - clouds are defined by their altitude (height), shape, and formation

21. What is Weather? a. Stratiform Clouds - formed by horizontally blowing winds - thick layers of clouds

22. What is Weather? b. Cumuliform Clouds - formed by vertically rising air - big and puffy clouds - cumulus clouds - big, puffy, fair weather clouds - usually formed under high pressure

23. What is Weather? - cumulonimbus – thunderheads- massive, anvil-shaped clouds - stratus clouds - close to ground, make thick layers - nimbostratus - thick, low- lying, precipitation causing clouds - cirrus - high, thin, wispy clouds - made of ice crystals

24. What is Weather? 2. Precipitation - water falling out of the atmosphere - may be either solid or liquid a. rain - liquid water b. snow - 6 sided ice crystal, no 2 are alike c. sleet - ice pellets

25. What is Weather? d. freezing rain - supercooled water - water cooled to lower than 0º C - water has no surface to freeze on - water comes out of the atmosphere - freezes to make a layer of ice upon contact with a surface with a temperature = or < 0  C

26. What is Weather? e. hail - similar to sleet in its structure - only occurs during summer months during thunderstorms and other severe weather - form by updrafts of air - can be as small as a grain of sand or as large as a grapefruit (and possibly larger) - water needs a condensation nucleus to form - substance for water to freeze on ex.: volcanic ash, salt crystals, dust