the sun and the seasons 1. introduction 2. solar energy 4
TRANSCRIPT
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THE SUN AND THE SEASONS
1. Introduction
2. Solar energy
3. Variation and the solar constant
4. Seasons
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LITHOSPHERE
BIOSPHERE
Source: After
Christopherson,
2012, p. 13
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The Solar System. Source: Christopherson, 2012, p. 41.
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Earth-Sun size comparison. Source: Christopherson, 2009, p. 44.
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The Sun imaged by SOHO. Source: Christopherson, 2009, p. 44.
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The Sun imaged by SOHO. Source: Christopherson, 2012, p. 42.
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Energy production in the Sun: hydrogen fusion.
Hydrogen atoms
Helium atom
Energy
Squeezed together by
Sun’s immense gravity
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PROCESSES OF ENERGY TRANSFER:
HOW DOES IT GET FROM (A) TO (B)?
1. Convection: vertical mixing currents
2. Conduction: two surfaces touching
3. Advection: warm or cold air moves
horizontally
4. Radiation: via electromagnetic waves,
making no use of intervening medium
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Wavelength and frequency. Source: Christopherson, 2012, p. 44.
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0.4 µm 0.5 µm 0.6 µm 0.7 µm
Visible light 0.4 to 0.7 µm
The electromagnetic spectrum
Wavelength (λ)
gamma
rays x-rays
ultraviolet
visible light
infrared
microwaves
radio waves
COLOURS OF THE
RAINBOW:
ROY G. BIV
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Solar output by
wavelength.
Source: Christopherson, 2012,
p. 45.
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CAUSES OF VARIABILITY IN SOLAR
ENERGY RECEIVED BY EARTH
1. Solar output
2. Distance from the Sun
3. Atmospheric absorption and reflection
4. Where on Earth? (Sun angle)
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Earth-Sun size comparison. Source: Christopherson, 2009, p. 44.
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Changes in solar output: the effect of sunspots
Sunspots
Emitted solar radiation
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Sunspot numbers and
solar irradiance. Source: Lean, 2010.
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The 11-year
sunspot cycle
and the Maunder
Minimum.
Source: Barry and Chorley, 1992.
Maunder Minimum
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The Little Ice Age, c. 1450-1850.
Caused by the Maunder Minimum??
Figures on a Frozen Canal, Gerrit van Battem, 1670-1680. Source: J. Paul Getty Museum.
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Perihelion
January 3rd Aphelion
July 4th
7% difference in insolation
Distance from the sun also influences solar radiation
received, because the Earth has an elliptical orbit:
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Valley fog and inversion in Salt Lake Valley,
December 2004.
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Valley fog and inversion in Salt Lake Valley,
December 2004.
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Global dimming:
reduced surface
insolation due to
air pollution.
Source: Romanou et al., 2006.
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Estimated global temperature change since 1860.
Source: The heat is on, The Economist, 2011.
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Effects of Earth’s curvature. Source: Christopherson, 2012, p. 46.
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Effects of Earth’s curvature. Source: Mann and Kump, 2009, p. 10.
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DEFINING THE SOLAR CONSTANT:
What variations need to be accounted for?
1. Average INSOLATION
2. Average DISTANCE FROM THE SUN
3. At the SUBSOLAR POINT
4. At the top of the atmosphere
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Taking into account all of these
sources of variation, the solar
constant has been most accurately
measured as
1372 W/m2
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What causes seasons?
Can your explanation account for the
temperature data in the handout?
Is there a better
explanation? How?
YES NO
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Earth’s surface experiences variations in:
•DAY LENGTH
•HEIGHT OF THE SUN IN THE SKY
These variations result from
SEASONAL CHANGES
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Earth’s revolution and rotation. Source: Christopherson, 2012, p. 49.
1 complete revolution
every 365 ¼ days.
1 complete rotation every 24 hours.
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Axial tilt and the plane of the ecliptic.
Source: Christopherson, 2009, p. 53;
see Christopherson, 2012, p. 50.
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Arctic circle
Sun’s rays
EQUINOX:
September 22
EQUINOX:
March 21
SOLSTICE:
June 21
SOLSTICE:
December 21
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Solstices and equinoxes. Source: Christopherson, 2012, p. 51.
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Antarctic circle
66.5° south
Arctic circle
66.5° north
Equator (0°)
Tropic of Cancer
23.5° north
Tropic of Capricorn
23.5° south
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Sun angle changes with seasons. Source: Christopherson, 2012, p. 53.