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Chapter 24

Chapter 24. Weather and Climate. 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. Composition of Atmosphere. 78 % is nitrogen 21% is oxygen

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Chapter 24

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  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.

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

  4. 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

  5. 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

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

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

  8. 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

  9. 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

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

  11. 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

  12. 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

  13. 24.2 The Sun and the Season

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

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

  16. Latitude Zones

  17. 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

  18. 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

  19. 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

  20. 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

  21. 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

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

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

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

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

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

  27. 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

  28. 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

  29. 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

  30. 24.5 Weather Patterns • Consists of • Warm Fronts • Stationary Fronts • Occluded Fronts • cold Fronts

  31. 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

  32. 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

  33. 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

  34. 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

  35. 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

  36. 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

  37. 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

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

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

  40. 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

  41. 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

  42. 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

  43. 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

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

  45. 24.6 Predicting the Weather • Meteorologists study Earth’s weather • They use: • Doppler radar • Automated weather stations • Weather satellites • High- speed computer

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