Ch. 6 Weather and Climate

1. Ch. 6Weather and Climate Mrs. Sealy APES

2. Weather • The short-term day-to-day changes in temperature, air pressure, humidity, precipitation, sunshine, cloud cover and wind direction and speed. • Most weather is predicted using: weather balloons, aircraft, radar, and satellites

3. Weather Changes • Air Masses: large lump of air that similar temperature and moisture level throughout. • Air Masses that effect the US are

4. When air masses meet it causes changes in weather • Cold front: when a cold air mass collides with a stationary warm air mass. The result is: thunderstorms, short bursts of heavy rain

5. Warm Front: • when a warm air mass collides with a stationary cold air mass. The result is: warm steady rain

6. Weather is also affected by changes in atmospheric pressure • High pressure has descending air that moves outward from the center of the high-pressure system. Descending air is warm and dry. The result is: nice dry weather

7. Low pressure • has ascending air that flows towards the center of the low-pressure area. Ascending air-cools and condenses as it rises. The result is: clouds, rain

8. Weather Extremes • Hurricanes: • What is it? Tropical storm with winds greater than 75 mph • The bad: loss of life and property • The good: flushes out coastline

9. Tornadoes: • Form when cold dry air collides with warm moist air, which causes the warm air to rise quickly making a funnel cloud

10. Prince Williams Sound Gulf of Alaska Risk of Tornadoes CANADA Highest High Medium UNITED STATES Low Grand Banks Hurricane Frequency High Moderately high Atlantic Ocean MEXICO Fig. 6.2, p. 122

11. Climate • Climate is the long term average precipitation and temperature of an area • Climate is determined by global wind patterns, latitude, altitude and ocean currents

12. Climate is the average weather patterns for an area over a long period of time (30 - 1,000,000 years). It is determined by and Average Temperature Average Precipitation which are influenced by latitude altitude ocean currents and affects Fig. 6.3, p. 123 what they grow and eat where people live how people live

13. Warm ocean current Warm temperate Highland Polar (ice) Cold ocean current Dry Major upwelling zones Subarctic (snow) Fig. 6.4, p. 124 River Tropical Cool temperate

14. Global Air currents affect regional climates • Uneven heating of the Earth’s surface causes the equator to receive more sunlight making it hotter; the poles receive less light making them cooler. This causes: global circulation

15. Easterlies (from the east) Westerlies (from the west) 60°N Northeast tradewinds 30°N (Doldrums) equator Southeast tradewinds 30°S Westerlies Easterlies 60°S Deflections in the paths of air flow near the earth’s surface  Initial pattern of air circulation Fig. 6.6b, p. 125

16. Cold Cool Temperate Warm Temperate Tropical (equator) Tropical Warm Temperate Cool Temperate Cold Fig. 6.6a, p. 125 Climate type

17. Seasons • Seasonal changes in temp and precipitation affect climate because the earth is tilted on its axis. It is colder in the winter and warmer in the summer because:

18. ° 23.5 Spring (sun aims directly at equator) Winter (northern hemisphere tilts away from sun) Solar radiation Summer (northern hemisphere tilts toward sun) Fig. 6.5, p. 124 Fall (sun aims directly at equator)

19. Coriolis Effect • Rotation of the Earth on its axis prevents air currents from moving directly north or south causing the winds to curve in what is called:

20. Ocean Currents • Long term variations in the amount of incoming solar radiation • Heat from the sun evaporates water and transfers energy from the ocean to the atmosphere. This creates convection cells that transport heat to different latitudes. This leads to: ocean currents and weather

21. Warm ocean current Warm temperate Highland Polar (ice) Cold ocean current Dry Major upwelling zones Subarctic (snow) Fig. 6.4, p. 124 River Tropical Cool temperate

22. Ocean Currents Affect climate • Differences in water temp, winds and the rotation of the earth create currents. • Currents redistribute heat. For example the gulf stream brings heat to Europe

23. Upwelling is created when the trade winds blow offshore pushing surface water away from land. The outgoing surface water is replaced by nutrient bottom water. Upwelling support:

24. Wind Movement of surface water Diving birds Fish Upwelling Zooplankton Phytoplankton Nutrients Fig. 6.9, p. 126

25. The El Nino Southern Oscillation occurs every few years in the Pacific Ocean • In an ENSO, prevailing westerly winds weaken or stop • Surface waters along the coast of North America and South America (west) become warmer • Normal upwelling stops • This reduces the population of some fish species • Also causes severe weather, storms in the US especially CA, and drought in southeast Asia

26. Surface winds blow westward EQUATOR SOUTH AMERICA Warm waters pushed westward AUSTRALIA Warm water Thermocline Cold water Normal Conditions Fig. 6.10a, p. 127

27. +3 1982–83 1997–98 El Nino conditions La Nina conditions +2 +1 Temperature/Change (°F) 0 -1 -2 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 Year Fig. 6.12, p. 128

28. Winds weaken, causing updrafts and storms Drought in Australia and Southeast Asia EQUATOR Warm water flow stopped or reversed SOUTH AMERICA AUSTRALIA Warm water deepens off South America Warm water Thermocline Cold water El Niño Conditions Fig. 6.10b, p. 127

29. El Niño Drought Unusually high rainfall Unusually warm periods Fig. 6.11, p. 127

30. La Nina • La Ninas follow an El Nino and are characterized by cooling trends. La Nina brings more Atlantic hurricanes, colder winters in the north and warmer winters in the south, and an increase in tornadoes.

31. The chemical makeup of the atmosphere affects the weather. Small amounts of water vapor, carbon dioxide, ozone, methane, nitrous oxide and chlorofluorocarbons trap heat in the atmosphere warming the planet. These gases are called: greenhouse gases • The greenhouse effect is when greenhouse gases allow light, infrared radiation and UV radiation through to the surface of the earth where it is reflected back into space. The greenhouse gases trap some reflected infrared radiation

32. (a) (b) (c) Rays of sunlight penetrate the lower atmosphere and warm the earth's surface. The earth's surface absorbs much of the incoming solar radiation and degrades it to longer-wavelength infrared radiation (heat), which rises into the lower atmosphere. Some of this heat escapes into space and some is absorbed by molecules of greenhouse gases and emitted as infrared radiation, which warms the lower atmosphere. As concentrations of greenhouse gases rise, their molecules absorb and emit more infrared radiation, which adds more heat to the lower atmosphere. Fig. 6.13, p. 128

33. Ozone Layer • The ozone layer is located in the stratosphere. It is created when ultraviolet light turns oxygen into ozone. The chemical reactions is: • Ozone blocks all short wavelength UV-C radiation, 50% of the UV-B radiation and almost no long wavelength UV-A radiation. • Ozone also forms a thermal cap which: traps heat

34. Topography of the earth also creates microclimates A microclimate is small area that has a different climate than the general climate of an area. • Vegetation in an area influences climate: forests stay warmer in the winter and cooler in the summer because of the trees • Cities create heat islands that trap heat and decrease wind speeds

35. Water also changes climate by causing land breezes and sea breezes Cool air descends Warm air ascends Land warmer than sea; breeze flows onshore Fig. 6.15a, p. 130

36. Cool air descends Warm air ascends Land cooler than sea; breeze flows offshore Fig. 6.15b, p. 130

37. a Winds carry moisture inland from Pacific Ocean b Clouds, rain on windward side of mountain range c Rain shadow on leeward side of mountain range 4,000/75 3,000/85 2,000/25 1,800/125 1,000/25 Moist habitats 1,000/85 15/25 The rain shadow effect changes climate Fig. 6.14, p. 129