Chapter 2 Solar Energy to Earth and the Seasons

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Chapter 2Solar Energy to Earth and the Seasons

• Geosystems 6e
• An Introduction to Physical Geography

Robert W. Christopherson Charles E. Thomsen
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The Solar System, Sun, and Earth  

• Solar system formation and structure  
• Gravity
• Mutual attracting force exerted by the mass of an
  object on all other objects
• Planetesimal hypothesis
• Explains the formation of planets and other
  celestial bodies
• A nebular cloud of dust, gas, and icy comets
  condensed to form universe

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Dimensions and Distances

• Speed of light
• Light travels 6 trillion miles per year
• The distance light travels in a year is called a
  light year (ly)
• Milky Way Galaxy 100,000 ly across
• Our Solar System 11 light-hours across
• Moon is 1.28 light-seconds away

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Milky Way Galaxy
Figure 2.1
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Our New Solar System
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Solar Energy From Sun to Earth  

• The Sun
• Intercepted energy at the top of the atmosphere 
• The suns principle outputs
• Radiant energy and solar wind  

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Solar Activity and Solar Wind

• Solar wind clouds of electrically charged
  particles
• Sunspots are caused by magnetic storms. These
  cause changes in the solar output.
• Sunspots have activity cycle of 11 years

Figure 2.2
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Transmission of Energy

• Conduction molecule to molecule transfer of
  energy as it diffuses through a substance.
• Hot pan hand
• Convection transfer of energy by physical mixing
  involving strong vertical motion.
• Steam rising from boiling water

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Transmission of Energy

• Advection transfer of energy by physical mixing
  involving strong horizontal motion.
• Air rushing in through an opened door
• Radiation emission and propagation of energy in
  the form of EM waves
• sunlight

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The Electromagnetic Spectrum

• EM Spectrum all the radiant energy produced by
  the sun placed in an ordered range, divided by
  wavelength
• Weins Law hotter objects emit shorter
  wavelengths
• Shorter wavelengths have higher energy
• Sun radiates shortwave energy
• Earth radiates longwave energy

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Earths Energy Budget
Figure 2.8
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Distribution of Insolation

• Insolation Radiation arriving at the Earths
  atmosphere and surface
• Solar constant the amount of solar radiation
  received in the atmosphere
• Subsolar point the point on Earth where the
  suns rays are perpendicular to the surface
  maximum insolation received

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Distribution of Insolation

• Tropics receive more concentrated insolation due
  to the Earths curvature
• Tropics receive 2.5X more than poles
• Solar rays pass through more atmosphere before
  reaching the poles, so more energy is lost to
  scattering, absorption, and reflection

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Figure 2.9
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• Solar declination latitudinal change of
  subsolar points

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The Seasons  

• Seasonality the variation of the suns position
  over the horizon the changing daylength during
  the year  
• Seasons result from
• variations in the suns altitude angle between
  the horizon and the sun
• the sunss declination latitude of the subsolar
  point
• and daylength - duration of exposure to
  insolation 

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Reasons for Seasons 

• Variations in the suns altitude, declination,
  and daylength are caused by
• Revolution
• Rotation
• Tilt of Earths axis
• Axial parallelism
• Sphericity

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Reasons for Seasons 

• Revolution
• Earth revolves around the Sun
• One complete revolution is 365.25 days
• Orbit is elliptical, not circular
• Rotation
• Earth rotates on its axis once every 24 hours
• Earth rotates counter-clockwise

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Revolution and Rotation
Figure 2.13
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Reasons for Seasons 

• Tilt of Earths axis
• Axis is tilted 23.5 from plane of ecliptic
• Axial parallelism
• Axis maintains alignment during orbit around the
  Sun
• North pole points toward the North Star (Polaris)
• Sphericity

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Axial Tilt and Parallelism
Figure 2.14
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Annual March of the Seasons

• Winter solstice December 21 or 22
• Subsolar point Tropic of Capricorn
• Spring equinox March 20 or 21
• Subsolar point Equator
• Summer solstice June 20 or 21
• Subsolar point Tropic of Cancer
• Fall equinox September 22 or 23
• Subsolar point Equator

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Annual March of the Seasons
Figure 2.15
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End of Chapter 2

• Geosystems 6e
• An Introduction to Physical Geography

Robert W. Christopherson Charles E. Thomsen