4.7 Solar Radiation and Earth's Seasons

Insolation

Incoming Solar Radiation

Insolation = Solar Radiation/Area

• Changes due to the shape of the earth

• The surface most perpendicular to the sun will have the highest concentration of solar radiation per unit area (highest insolation)

• The angle of incidence decreases moving towards the poles, increasing the area of incidence, which in turn lowers insolation

Earth’s tilted axis

• Insolation varies by latitude because the angle of incidence changes

• Amounts of radiation from the sun doesn’t change

  • North pole

  • Arctic Circle (60 degrees N)

  • Tropic of Cancer (30 degrees N)

  • Equator

  • Tropic of Capricorn (30 degrees S)

  • Antarctic Circle (60 degrees S)

  • South pole

Seasons in the Northern Hemisphere

• September 22-23: Autumnal Equinox (Day and night roughly equal in length)

• December 21-22: Winter solstice (shortest day of the year) (Polar night in Arctic: no sunlight 24-7)

• March 20-21: Vernal Equinox (Day and night roughly equal in length)

• June 20-22: Summer Solstice (Longest day of the year) (Midnight Sun in Arctic)

Seasons in the Southern Hemisphere

• Opposite of the Winter hemisphere

• However, Equinox days are the same