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Chapter 3

Chapter 3 . Earth’s Seasons. Seasonal & Temperature Variations. Assignment. Read p. 56 – 61 and 71-75 Define terms: Summer solstice Autumnal equinox Winter solstice Vernal equinox Isotherms Mean daily temperatures Annual range of temperature Heating degree day Cooling degree day.

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Chapter 3

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  1. Chapter 3 Earth’s Seasons Seasonal &TemperatureVariations

  2. Assignment • Read p. 56 – 61 and 71-75 • Define terms: • Summer solstice • Autumnal equinox • Winter solstice • Vernal equinox • Isotherms • Mean daily temperatures • Annual range of temperature • Heating degree day • Cooling degree day

  3. Earth’s Orbit and Seasons • Earth orbits the sun once every 365.25 days. • Elliptical Orbit – Earth is closest to sun in northern hemisphere winter, farthest in summer.

  4. Earth’s Seasonal Variations • Our seasons are regulated by the amount of incoming solar radiation (insolation) received at the surface. • That amount is determined by 2 things: • Angle of the sun • Length of daylight How Close The Earth Is To The Sun Matters Far Less!

  5. Earth’s Seasonal Variations • Angle of the Sun • Higher sun angle: • More direct radiation over a smaller area. • Less atmosphere to pass through means less scattering and absorption by air molecules.

  6. Earth’s Seasonal Variations • Length of Day • Longer Daylight Hours: • More energy is available from the sun. • Provides more opportunity for warmth (~ 14 hours). • Shorter Daylight Hours: • Less energy is available from the sun. • Provides less opportunity for warmth (≤ 8 hours).

  7. Earth’s Orbit & Seasons • Northern Hemisphere: • Astronomical Summer begins June 21 • Summer Solstice • The sun’s rays are most direct in the northern hemisphere. • Days are very short (≤8 hours of sunlight) • Sun is higher in the sky. • Astronomical Fall begins September 20 • Vernal Equinox • The sun gets lower in the sky. • Days get longer and direct rays cross the equator.

  8. Daily Temperature Variations • Daytimewarming • Insolation strikes the ground and heats the surface. • in the lowest layers heats air molecules in contact with the ground. • Conduction in the lowest layers heats air molecules in contact with the ground • Air is a poor conductor, so conduction can’t transfer all the heat upward. • Through convection, thermals transport energy up and away from the surface.

  9. Daily Temperature Variations • DaytimeHeating • Sun is highest at noon, but maximum temp isn’t reached until afternoon. • Lag between maximum insolation and outgoing radiation. MorningLows DaytimeHighs Around Sunrise Late Afternoon/Evening

  10. Daily Temperature Variations • Daytime Heating • On a calm, sunny day, the air near the surface can be much warmer than the air a few meters above it. • Big temp diff. between our feet and head. • On a windy day, mechanical mixing stirs up the lowest few inches and distributes heat upward. • Temp diff. is minimal in the lowest few feet.

  11. Daily Temperature Variations • NighttimeCooling • Sun goes down. • Ground radiates energy out to space. • (radiational cooling) • Conduction of heat from lowest few inches of air into ground (molecule to molecule), then out to space. • Air closest to ground loses heat rapidly, forming a nocturnal radiation inversion.

  12. Daily Temperature Variations • Nocturnal Radiation Inversion • To get a strong inversion: • Calm Winds • No Clouds • Low Moisture Content • Long Night

  13. Daily Temperature Variations • Calm NightBetter Temp. InversionC O L D E R • Windy NightPoor Temp. InversionW A R M E R

  14. Daily Temperature Variations • Low Temperatures • Around Sunrise • Outgoing energy exceeds incoming energy. • High Temperatures • Late Afternoon and Early Evening • Incoming energy exceeds outgoing energy. • The Effects of Clouds & Heating • Cloudy Skies (at night) Act As A Blanket • Keeps the outgoing radiation at the surface. – Warm. • Clear Skies (at night) Allows For Heat Release • Allows the outgoing radiation to escape. – Cool.

  15. Daily Temperature Variations

  16. Daily Temperature Variations

  17. The Controls of Temperature • Four Controls of Temperature: • Latitude • Land and Water Distribution • Ocean Currents • Elevation

  18. The Controls of Temperature • Latitude: • On average, temperatures decrease over land masses as we move from the equator to the poles. • Lower sun angle and shorter days over the poles.

  19. The Controls of Temperature • Land/Water Distribution: • Water has a high heat capacity(slow to heat and cool). • Water distributes heat through it’s depth. • Areas near coastlines benefit from warm water in winter and cool water in summer. • Water moderates local climate. • Sea/Lake Breezes • Lake Effect Snow Oceans act as huge heat reservoirs!

  20. The Controls of Temperature • Ocean Currents: • Transport warmer water near equator toward the poles. • Example: Gulf Stream moves warm water near the Caribbean toward Northern Europe. • Elevation: • Air density decreases with elevation. • Fewer air molecules to warm by conduction.

  21. Air Temperature Data • Diurnal Temperature Range: The difference between the maximum and minimum temperatures in one day. • Larger on a sunny day than a cloudy one. • Larger on a dry day than humid one. • Larger over man-made surfaces (like pavement). • Mean Daily Temperature: Average of highest and lowest day’s temperatures.

  22. Air Temperature Data • Annual Range of Temperature: • Difference between the average temperature of the warmest and coldest month in one location. • Average Annual Temperature: • Average of 12 monthly temperatures. Columbia Average Monthly Temperatures Columbia Average Annual Temp: 55°F

  23. Using Temperature Data = 54° 11 HDD • Heating Degree Day (HDD) • Assumes people use their heater when the average daily temperature drops below 65°F. • Used by electric companies estimate usage. • Subtract the mean daily temperature from 65°F. Example: Max: 62°F Min: 46°F Daily Average Temp: (62+46) 2 Heating Degree Days: 65°F – 54°F =

  24. Using Temperature Data = 77° 12 CDD • Cooling Degree Day (CDD) • Assumes people use their AC when the average daily temperature is higher than 65°F. • Used by electric companies to estimate usage. • Subtract 65°F from the average daily temperature . Example: Max: 84°FMin: 70°F Daily Average Temp: (84+70) 2 Cooling Degree Days: 77– 65=

  25. Using Temperature Data = 77° 27 GDD Corn is typically harvested after 2200 GDD • Growing Degree Day (GDD) • Farmers use it for planting and harvesting dates. • Subtract the plant’s base temperature from the average daily temperature. • Corn Temperature: 50°F • Soybean Temperature: 40°F Example: Max: 84°F Min: 70°F Daily Average Temp: (84+70) 2 Growing Degree Days Corn: 77°F – 50°F =

  26. Air Temperature & Humans • Exchange of heat between the body and the environment determines how comfortable we really are. • Wind Chill Index (WCI): Based on temperature and wind speed 5 feet off of the ground. • Higher wind speed accelerates heat loss from skin. • Heat Index (HI): Based on temperature and humidity. • High humidity prevents perspiration from evaporating and cooling the body.

  27. Assignment Questions for review- p.82 (1-6, 17-21) Activity: Angle of Sunlight Worksheets: calculating HDD/CDD, Heating the Atmosphere

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