THE SUN AND THE SEASONS
1. Introduction
2. Solar energy
3. Variation and the solar constant
4. Seasons
LITHOSPHERE
BIOSPHERE
Source: After
Christopherson,
2012, p. 13
The Solar System. Source: Christopherson, 2012, p. 41.
Earth-Sun size comparison. Source: Christopherson, 2009, p. 44.
The Sun imaged by SOHO. Source: Christopherson, 2009, p. 44.
The Sun imaged by SOHO. Source: Christopherson, 2012, p. 42.
Energy production in the Sun: hydrogen fusion.
Hydrogen atoms
Helium atom
Energy
Squeezed together by
Sun’s immense gravity
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
Wavelength and frequency. Source: Christopherson, 2012, p. 44.
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
Solar output by
wavelength.
Source: Christopherson, 2012,
p. 45.
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)
Earth-Sun size comparison. Source: Christopherson, 2009, p. 44.
Changes in solar output: the effect of sunspots
Sunspots
Emitted solar radiation
Sunspot numbers and
solar irradiance. Source: Lean, 2010.
The 11-year
sunspot cycle
and the Maunder
Minimum.
Source: Barry and Chorley, 1992.
Maunder Minimum
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.
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:
Valley fog and inversion in Salt Lake Valley,
December 2004.
Valley fog and inversion in Salt Lake Valley,
December 2004.
Global dimming:
reduced surface
insolation due to
air pollution.
Source: Romanou et al., 2006.
Estimated global temperature change since 1860.
Source: The heat is on, The Economist, 2011.
Effects of Earth’s curvature. Source: Christopherson, 2012, p. 46.
Effects of Earth’s curvature. Source: Mann and Kump, 2009, p. 10.
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
Taking into account all of these
sources of variation, the solar
constant has been most accurately
measured as
1372 W/m2
What causes seasons?
Can your explanation account for the
temperature data in the handout?
Is there a better
explanation? How?
YES NO
Earth’s surface experiences variations in:
•DAY LENGTH
•HEIGHT OF THE SUN IN THE SKY
These variations result from
SEASONAL CHANGES
Earth’s revolution and rotation. Source: Christopherson, 2012, p. 49.
1 complete revolution
every 365 ¼ days.
1 complete rotation every 24 hours.
Axial tilt and the plane of the ecliptic.
Source: Christopherson, 2009, p. 53;
see Christopherson, 2012, p. 50.
Arctic circle
Sun’s rays
EQUINOX:
September 22
EQUINOX:
March 21
SOLSTICE:
June 21
SOLSTICE:
December 21
Solstices and equinoxes. Source: Christopherson, 2012, p. 51.
Antarctic circle
66.5° south
Arctic circle
66.5° north
Equator (0°)
Tropic of Cancer
23.5° north
Tropic of Capricorn
23.5° south
Sun angle changes with seasons. Source: Christopherson, 2012, p. 53.