Chapter 24

1. Chapter 24 Weather and Climate

2. 24.1 The Atmosphere • It’s the protective layer that surrounds Earth • It protects Earth from UV rays • It moderates the temperature • It contains gases that are essential for life.

4. Composition of Atmosphere • 78% is nitrogen • 21% is oxygen • The remaining 1% is a mixture of water vapor and other gases

5. Air Pressure • The force of gravity pulling the atmosphere toward Earth causes air pressure. • It is equal to 101,325 Newton per square meter at sea level • Pressure decreases as altitude increases • Density decreases as altitude increases

6. Barometer • Air pressure is measured with a barometer • A mercury barometer measures pressure at sea level at 760 mm Hg • It uses a column of Hg to measure pressure

7. Aneroid Barometer • More portable than a mercury barometer • It uses a metal chamber to measure pressure

8. Atmospheric layers • Temperature drops as altitude increase • Changes in temperatures define the layers in the atmosphere

10. Troposphere • Lowest layer • Contains almost all of the water vapor and suspended particles • Weather happens here • 9 km at poles 12 km at the equator • Temperature decreases by 6.5° per km

11. Stratosphere • Next Layer • 12 km to 50 km above the earth • Temperature remains the same near the boundary of the troposphere then increase after about 20km • The ozone layer warms the upper stratosphere by absorbing UV radiation

12. Mesosphere • The layer above the stratosphere • 50km to 80km • Gets cooler the higher it gets • Most meteoroids burn up in this layer

13. Thermosphere • Outer most layer • Gets warmer as it gets further from earth • Starts at -90°C and goes to 1000°C • It has no upper boundary but instead gradually enters outer space

14. Ionosphere • Not a layer but instead a region of charged particles that covers the thermosphere • AM radio waves bounce back to earth from the ionosphere • Aurora is a colorful display at night occurs when charged particles from the sun are attracted to Earth’s Magnetic poles

16. 24.2 The Sun and the Season

17. Rotation • Spinning of Earth on its axis • Takes 24 hours

18. Revolution • The movement of one body in space around another • Earth’s movement around the sun • Takes 365 days

19. Latitude Zones

20. The Season • Earth is on a tilt of 23.5° N • It is the cause of the season • Seasons are NOT caused by the distance from the sun. In fact, the Earth is closest to the sun during winter in the Northern hemisphere

22. Solstices • Occurs when the Sun is directly overhead at 23.5 ° N and 23.5 ° S • Northern hemisphere it occurs on June 21st • Daylight hours are longest in the northern hemisphere and shortest in the southern hemisphere • December 21st is the winter solstice and the reverse occurs

23. Equinoxes • Days are about equal darkness and light • Occurs approximately half way between solstices • Neither hemisphere is tilted toward the sun • Vernal equinox occurs on March 21 • Autumnal equinox occurs September 22

24. 24.3 Solar Energy and Winds • Most of the energy that heats the troposphere is radiated from Earth • The greenhouse effect reflects that energy back toward the Earth

26. Wind • Caused by differences in air pressure • Differences in air pressure caused by unequal heating of Earth’s surface • Warm air expands and rises • Cooler air is denser and moves to take its place

27. Local Winds • Wind that occurs in a small area • Caused by unequal heating in a small area • Sea breezes are an example

28. Global Winds • Winds that blow in specific direction • Move in bands called convection bands • Examples are trade winds, westerlies and polar easterlies

29. The rotation of the Earth causes the winds to turn – Coriolis effect

30. Monsoons • Characterized by reversal in weather over a large region for a large amount of time.

31. Jet Stream • Fast moving stream of air that occur because of great differences in air pressure that develop at high altitudes

32. 24.4 Water in the Atmosphere • Humidity – amount of water vapor in the air • Relative humidity is the ratio of the amount of water vapor in the air • Expressed in percentage • Cooler air holds less water vapor than warm air • Dew point is the temperature at which water condenses

33. Cloud Formation • Form as warm, moist air rises and water vapor condenses in the atmosphere • Must have solid suspended particles to form • When water vapor is cooled below its dew point, water vapor condenses onto these particles

34. Precipitation • Rain, sleet, snow, hail, and freezing rain • Rain forms in nimbostratus clouds or cumulonimbus clouds • Hail is ice of more than 5 mm in diameter • Sleet is ice smaller than 5mm • Freezing rain is rain that freezes after it hits the surface

35. 24.5 Weather Patterns • Consists of • Warm Fronts • Stationary Fronts • Occluded Fronts • cold Fronts

36. Air Masses • Large body of air that covers a large area and has uniform properties • They are classified by how they are formed over land or water and the latitude where they form

37. Fronts • After air masses form, they move • When they move they meet other air masses and form a front • Cold front • Warm front • Stationary front • Occluded front

38. Cold Fronts • Fronts when a cold air mass overtakes a warm air mass • Produces cumulus and cumulonimbus clouds • Produces severe thunderstorms, precipitation, and strong winds

39. Warm Fronts • Occurs when a warm air mass overtakes a cold air mass • Stratus clouds forms • May have a steady rain, may have some thunderstorms • Temperature rises after the front passes

40. Stationary Fronts • Occur when two unlike fronts meet but do not overtake one or the other • May results in clouds and steady rain or snow for several days

41. Occluded Fronts • Forms when a warm air mass is caught between two cooler air masses. • The cooler masses cut the warm air mass off from the ground. The warm air rises and cools • Results in cloudy skies and precipitation

42. Cyclones • Low air pressure in the center • Rotates counterclockwise in the Northern Hemisphere • Doesn’t stay in one place • Associated with strong winds and precipitation

43. Anticyclones • Center is a high air pressure • Rotate clockwise in the Northern hemisphere • Has clear skies, very little precipitation, and generally calm conditions

44. Storms • Thunderstorms • Tornadoes • Tropical Storms and Hurricanes

45. Thunderstorms • Small weather system that includes thunder and lightning • Accompanied by strong winds and heavy rain or hail • Occur when columns of air rise within a cumulonimbus cloud

46. Lightning • Sudden electrical discharge in the atmosphere • Positive charges accumulate at the top of the cloud, negative charges at the bottom • When there is enough difference in charge, lightning flashes

47. Thunder • Occurs from the expansion of gases that results from the extreme heat the released when lightning discharges • You hear thunder after you see lightning because light travels faster than sound

48. Tornadoes • A small but intense windstorm that is a rotating column of air that touches the ground • Usually occur at the leading edge of an advancing cold front • Occurs in a thunderstorm • Wind can reach 500 km/hr usually 150km/hr

49. Hurricanes • Cyclone that develop in the tropics • Hurricane is a large tropical cyclone with winds of at least 110 km/hr

50. 24.6 Predicting the Weather • Meteorologists study Earth’s weather • They use: • Doppler radar • Automated weather stations • Weather satellites • High- speed computer