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GEOG101 Chapter 4 Lecture
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GEOG101 Chapter 4 Lecture


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  • 1. Overview
    • Air Temperature
    • Air Pressure and Winds
    • Ocean Currents
    • Moisture in the Atmosphere
    • Climate Regions
    • Climatic Change
  • 2. Weather vs. Climate
    • Weather
      • State of the atmosphere at a given time and place
    • Climate
      • Long-term average weather conditions in a place
    • Troposphere is of particular concern
      • Atmospheric layer closest to the earth
      • Contains virtually all of the air, clouds, and precipitation of the earth
  • 3. Air Temperature
    • Insolation
      • Solar radiation received at the earth’s surface
        • Determined by angle of the sun’s rays and number of daylight hours
    • Modifying variables
      • Amount of water vapor in the air
      • Cloud cover
      • Nature of the surface of the earth
      • Elevation
      • Degree and direction of air movement
  • 4. Earth Inclination
    • Axis of the earth tilts at ≈ 23.5°
    • Summer Solstice (about June 21)
      • Northern hemisphere tilted toward the sun
      • Vertical rays of the sun at 23.5° N
    • Winter Solstice (about December 21)
      • Northern hemisphere tilted away from the sun
      • Vertical rays of the sun at 23.5° S
    • Spring and fall equinoxes (about March 21 and September 21)
      • Vertical rays of the sun at equator
  • 5. Earth Inclination
    • Variation in length of days and nights
      • At the equator
        • 12 hours of light each day of the year
      • Inside the Arctic Circle and Antarctic Circle
        • 24 hours of daylight/darkness on solstice
    • Angle of the sun’s rays
      • More direct angle = more energy available
  • 6. Reflection and Reradiation
    • Clouds and light colored surfaces reflect solar energy
    • Reradiation
      • Shortwave solar energy absorbed, returned into the atmosphere as longwave terrestrial radiation
    • Water heats and cools more slowly
      • Marine environment
        • Cooler summers, warmer winters
    • Land heats and cools more rapidly
      • Continental environment
        • Hotter summers, colder winters
  • 7. The Lapse Rate
    • Temperature generally decreases as altitude increases
      • Lapse rate
        • Average of 3.5° F per 1000 feet (6.4 ° C per 1000 m)
    • Temperature inversion
      • Cooler air trapped below warmer air
        • Contributes to smog problems
  • 8. Air Pressure and Winds
    • Weight of the atmosphere
    • Air pressure is higher closer to the earth’s surface
    • Temperature and air pressure
      • Cold air is denser: high pressure
      • Warm air is lighter: low pressure
    • Air pressure is measured by a barometer
  • 9. Air Pressure and Winds
    • Zones of high and low air pressure
    • Pressure gradient force
      • Causes air to flow from high to low pressure areas
      • Wind
        • Velocity is in direct proportion to pressure differences
    • Convection
      • Circulatory movement of rising warm air and descending cool air
  • 10. Air Pressure and Winds
    • Land and sea breezes
      • Day: from sea to land
      • Night: from land to sea
    • Mountain and valley breezes
      • Day: from valley to mountains
      • Night: from mountains to valley
  • 11. Air Pressure and Winds
    • Coriolis effect
      • Apparent deflection relative to the earth’s surface
        • Northern Hemisphere: wind veers toward the right Southern Hemisphere: wind veers toward the left
      • Spiral wind patterns
    • Frictional effect
      • Decreases wind speed
      • Changes wind direction
  • 12. Global Air-Circulation Pattern
    • Equatorial low pressure
    • Subtropical high pressure
      • About 30 ° N and 30° S of the equator
    • Trade winds
      • In the tropics
    • Westerlies
      • In the midlatitudes
    • Subpolar low
    • Polar easterlies
    • Polar high
  • 13. Global Air-Circulation Pattern
    • Jet streams
      • Belts of strong winds in the upper atmosphere
        • From west to east
      • Guide the movement of weather systems
    • Monsoon
      • Wind system that reverses direction seasonally
        • Produces wet and dry seasons
      • Significant effect on parts of southern and eastern Asia
        • Farm economy is dependent upon summer monsoon rains
        • Flooding
  • 14. Ocean Currents
    • Movement due to winds and differences in water density
      • Direction also influenced by landmasses and shape of ocean basins
    • North Atlantic drift
    • Ocean currents affect temperature and precipitation on adjacent land areas
      • Cold currents
        • Dry conditions
      • Warm currents
        • Moist conditions
  • 15. Moisture in the Atmosphere
    • Ascending air expands and cools
      • Less able to hold water vapor
    • Supersaturated air
      • Water vapor condenses around condensation nuclei
    • Clouds
      • Rain droplets or ice crystals supported by upward movements of air
        • Droplets may coalesce and fall as precipitation
      • Form and altitude depends on:
        • Water vapor content, temperature, wind movement
  • 16. Moisture in the Atmosphere
    • Relative humidity
      • Percentage measure of the moisture content of the air
        • Amount present relative to the maximum that can exist at the current temperature
    • Dew point
      • Temperature at which condensation forms
  • 17. Types of Precipitation
    • Convectional precipitation
      • Heated, moisture-laden air rises and then cools below the dew point
      • Summer in tropical and continental climates
    • Orographic precipitation
      • Warm, moisture-laden air is forced to rise over hills or mountains and is thereby cooled
        • Windward side
          • Receives a great deal of precipitation
        • Leeward side
          • Very often dry (rain shadow)
  • 18. Types of Precipitation
    • Cyclonic (frontal) precipitation
      • Cool and warm air masses meet
      • Common to the midlatitudes
      • In the tropics—originator of hurricanes and typhoons
      • Air mass
        • Body of air with similar temperature, pressure, and humidity characteristics throughout
        • Form over a source region
      • Front
        • Zone of separation between two air masses
  • 19. Storms
    • Cyclone
      • Masses of air circulate rapidly about a region of low atmospheric pressure
      • Can develop into a storm
    • Hurricane
      • Severe tropical cyclone with winds exceeding 75 mph
      • In the Atlantic, Caribbean, or Gulf of Mexico
    • Typhoon
      • Hurricane in the western Pacific
  • 20. Storms
    • Blizzard
      • Heavy snow and high winds
    • Tornado
      • Funnel-shaped cloud of whirling winds that can form beneath a cumulonimbus cloud and moves at speeds as high as 300 mph
      • Esp. Central U.S.
  • 21. Climate Regions
    • Generalizations based on daily and seasonal weather conditions
    • K öppen system
      • Based on temperature, precipitation, and natural vegetation criteria
      • A: tropical
      • B: dry
      • C: mild midlatitude
      • D: midlatitude with cold winters
      • E: polar
      • H: highland
  • 22. Tropical Climates
    • Tropical rainforest
      • Equatorial low pressure
      • High temperatures and heavy convectional rainfall all year
      • Dense forests
      • Lack of soil nutrients
  • 23. Tropical Climates
    • Tropical savanna
      • To the north and south of rain forests
      • High temperatures
      • Heavy convectional rainfall in summer, dry winters
      • Forests to grasslands
    • Tropical monsoon
      • Significant increase in rainfall when summer monsoon winds bring water-laden air
      • Dense forests
  • 24. Dryland Climates
    • Hot deserts
      • Subtropical high pressure
      • Considerable sunshine, high temperatures
      • Very little precipitation
      • Shrubs in gravelly or sandy environments
    • Midlatitude deserts and semideserts
      • Warm/hot summers and cold winters
      • Some convectional or frontal rainfall in summer, some snowfall in winter
      • Grasslands, desert shrubs
      • Steppes have fertile soils
  • 25. Humid Midlatitude Climates
    • Mediterranean
      • Transition zone between subtropical high and westerlies
      • Warm/hot summers and mild/cool winters
      • Dry summer, frontal precipitation in winter
      • Shrubs and small deciduous trees
    • Humid subtropical
      • Hot, moist summers and moderate, moist winters
      • Convectional rainfall in summer, frontal precipitation in winter
      • Deciduous and coniferous forests
  • 26. Humid Midlatitude Climates
    • Marine west coast
      • Prevailing winds from the sea
      • Moderate temperatures in both summer and winter
      • Frontal and orographic precipitation
      • Deciduous and coniferous forests
    • Humid continental
      • Prevailing winds from the land
      • Hot/mild summers and cool/cold winters
      • Frontal and occasionally convectional rainfall in summer, snow in winter
      • Deciduous and coniferous forests
  • 27. Arctic and Subarctic Climates
    • Subarctic
      • Cool/cold, short summers and very cold winters
      • Coniferous forest to mosses and lichens
      • Tundra
        • Treeless area between the Arctic tree line and the permanently ice-covered zone
    • Arctic
      • Ice cap near the poles
      • Extremely cold with light precipitation
  • 28. Highland Climates
    • Lower temperatures than lowlands at the same latitude
    • Variety of conditions based on:
      • Elevation
      • Prevailing winds
      • Orientation of slope relative to the sun
      • Valley, slope, or peak
      • Ruggedness
  • 29. Climatic Change
    • Long-term climatic change
      • Significant variations over geologic time
        • Ice ages
        • Medieval warm period and “little ice age”
      • May be due to variations in: shape of Earth’s orbit, tilt of the axis, gyration of the rotation axis
    • Short-term climatic change
      • Natural processes
        • Volcanic eruptions, oceanic circulation, sunspot activity
      • Human processes
        • Enhanced greenhouse effect
  • 30. Climatic Change
    • Greenhouse effect
      • Certain gases in the atmosphere function as an insulating barrier, trapping infrared radiation
    • Global warming
      • Caused by human activities that have increased the amount of greenhouse gases in the atmosphere
        • Carbon dioxide: burning fossil fuels, deforestation
        • Methane: natural gas and coal mining, agriculture and livestock, swamps, landfills
        • Nitrous oxides: motor vehicles, industry, fertilizers
        • Chlorofluorocarbons: industrial chemicals
  • 31. Climatic Change
    • Evidence of global warming
      • 20 th century was the warmest in 600 years
        • Average surface temp rose over 1 ° F during the century
      • Winter temps in the Arctic have risen about 7° F since the 1950s
        • Loss of Arctic ice cap
      • Glaciers are thinning and retreating
    • Consequences of global warming include:
      • Rising sea levels
      • Changes in temperature and precipitation patterns
        • Impact on soils, vegetation, agriculture