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.