1. Chapter 9 Meteorology

2. Section A, Weather Factors §Atmosphere l Comprised of: Oxygen - 21% Nitrogen - 78% Other gases - 1% l 99.9% of Atmosphere is within 30 miles

3. Section A, Weather Factors §Atmosphere is classified by thermal characteristics l Troposphere Lowest level contains most weather varies in altitude from 24,000’ to 50,000’ with about 36,000’ to 37,000’ in mid-latitudes characterized by a decrease in temp with increase in altitude

4. Section A, Weather Factors l Tropopause above troposphere characterized by an abrupt change in temp lapse rate l Stratosphere Severe thunderstorms may extend Tops about 160,000’

5. Section A, Weather Factors §Atmospheric circulation l Weather changes are caused by uneven heating l Every process of weather is the result of or is accompanied by a heat exchange l The sun is directly over the Tropic of Cancer on June 21

6. Section A, Weather Factors §Pressure and wind patterns l Pressure Highs - Center of high pressure, peak of hill Lows - Center of low pressure, bowl Cols - area between 2 highs, or lows Ridges - elongated area of high pressure Troughs - elongated area of low pressure

7. Section A, Weather Factors §Highs are usually associated with l Good visibility l Light winds l Few clouds l Good weather l Characterized by descending air

8. Section A, Weather Factors l Lows are usually associated with precipitation cloudiness poor visibility bad weather turbulence Wind characterized by rising air Example of lows are hurricanes and tornadoes

9. Section A, Weather Factors §Air tries to flow from high to low l At higher altitudes, Coriolis force makes the wind flow parallel with isobars l At lower altitudes, surface friction weakens Coriolis force and flows across the isobars l This airflow is wind

10. Section A, Weather Factors §In the northern hemisphere l Air flows counterclockwise around a low (cyclonic) l Air flows clockwise around a high (anticyclonic) l If one were to fly directly to the center of a low, the winds would come from the left and get stronger as one got closer

11. Section A, Weather Factors §Local wind patterns l Unequal heating of land and water Land and sea breezes l Mountain and Valley breezes On a larger scale these are Katabatic winds.

12. Section A, Weather Factors §Water l Solid - ice l Liquid - water l Gas - water vapor Odorless Colorless l Changes states by: Evaporation, Sublimation, Condensation, Deposition, Freezing and Melting

13. Section A, Weather Factors §Relative Humidity l Measure of how much moisture is present for a a parcel of air at a temperature. l If a parcel of air has a RH of 100%, it is saturated. The temperature that it is at is called the dewpoint. If this parcel were cooled more, water vapor would clouds, fog, dew or frost

14. Section A, Weather Factors §Precipitation - condensation nuclei l Drizzle l Rain l Snow l Ice pellets l Hail l Ice crystals

15. Section A, Weather Factors §For a heavy rain to occur, clouds must be at least 4000’ thick. §Virga §Wet snow