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WHAT CAUSES THE SEASONS AND ASSOCIATED CHANGES IN INSOLATION?

Seasons change due to the Earth's axial tilt and its orbit around the Sun, affecting insolation. Key dates, like March 21, June 21, September 21, and December 22, mark the solstices and equinoxes, leading to varying zenith angles. The sub-solar point is the latitude where the noon Sun is directly overhead, changing with the seasons. For instance, the zenith angle at noon is equal to a location's latitude minus the latitude of the sub-solar point. Understanding these patterns helps explain temperature variations and solar energy distribution worldwide.

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WHAT CAUSES THE SEASONS AND ASSOCIATED CHANGES IN INSOLATION?

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  1. WHAT CAUSES THE SEASONS AND ASSOCIATED CHANGES IN INSOLATION?

  2. September 21 December 22 June 21 SUN March 21

  3. WHAT DO WE KNOW SO FAR? March & September 21 Old School Geography N Sun on horizon z = 90° Noon z = Lat Arctic Circle 66.5°N S U N Tropic of Cancer 23.5°N Equator 0° Sun overhead z = 0° Tropic of Capricorn 23.5 °S Antarctic Circle 66.5°S Sun on horizon z = 90° S Gainesville, 29.5°N Southampton, 52°N Perth, W.A., 32°S Zenith Angle at noon on these two days is exactly equal to a location’s Latitude.

  4. WHAT IS THE SUB-SOLAR POINT? March & September 21 N Arctic C. S U N Cancer Equator Sun overhead z = 0° Capricorn Antarctic C. S Sub-solar point is the latitude at which the noon day Sun appears directly overhead (z=0) at noon.

  5. WHAT IS THE ZENITH ANGLE AT NOON ANYWHERE IN THE WORLD?

  6. WHAT IS THE ZENITH ANGLE AT NOON ANYWHERE IN THE WORLD? Z = LATITUDE OF LOCATION – LATITUDE OF SUB- SOLAR POINT Thus on March and September 21: Z at Noon = Latitude of location - 0

  7. WHAT IS THE SUB-SOLAR POINT FOR ANY DAY OF THE YEAR?

  8. WHAT THE *%$* ?

  9. WHAT THE *%$* ? ANALEMMA

  10. WHAT THE *%$* ? 23.5°N ANALEMMA Equator Latitude of Sub-solar point 23.5°S

  11. WHAT IS THE SUB-SOLAR POINT FOR ANY DAY OF THE YEAR?

  12. September 21 December 22 June 21 N SUN S March 21

  13. ANALEMMA 23.5°N June 21

  14. June 21 N Sun on horizon z = 90° S U N S Cancer Equator U Sun overhead z = 0° N Antarctic s Sun on horizon z = 90°

  15. June 21 N Sun on horizon z = 90° S U N S Cancer Equator U Sun overhead z = 0° N Equator: z = 23.5° Antarctic s Sun on horizon z = 90°

  16. WHERE IS THE SUN OVERHEAD (z=0) AT NOON? June 21 N Sun on horizon z = 90° S U N S Cancer Equator 23.5°N U Sun overhead z = 0° N Antarctic s Sun on horizon z = 90°

  17. WHAT IS NOONTIME Z IN GAINESVILLE? June 21 N Sun on horizon z = 90° S U N S Cancer Z = <29.5° = 29.5 – 23.5 = 6° Equator U Sun overhead z = 0° Lat = 29.5° N Antarctic s Sun on horizon z = 90° Small Zenith Angle: Sun CloseTo Overhead – Higher Proportion of Solar Constant – More Energy – HOT!

  18. WHAT IS NOONTIME Z IN SOUTHAMPTON? June 21 N Sun on horizon z = 90° S U N S Cancer Z = <52° = 52 – 23.5 = 28.5° Equator U Sun overhead z = 0° Lat = 52°N N Antarctic s Sun on horizon z = 90° Small Zenith Angle: Sun CloserTo Overhead – Higher Proportion of Solar Constant – More Energy – WARM!

  19. WHAT IS NOONTIME Z IN PERTH, W.A.? June 21 N Sun on horizon z = 90° S U N S Cancer Equator U Sun overhead z = 0° Lat = 32°S Z = >32° = 32 + 23.5 = 8.5° N Antarctic s Sun on horizon z = 90° Large Zenith Angle: Sun Further From Overhead – Lower Proportion of Solar Constant – Less Energy – COOLER!

  20. September 21 December 22 June 21 N SUN S March 21

  21. ANALEMMA 23.5°S December 22

  22. WHERE IS THE SUN OVERHEAD AT NOON? December 22 N Sun on horizon z = 90° S U N S Arctic Z = >0° = 0 + 23.5 = 23.5° U Sun overhead z = 0° Equator Capricorn N 23.5°S Sun on horizon z = 90° s

  23. WHAT IS ZENITH ANGLE AT GAINESVILLE? December 22 N Sun on horizon z = 90° Z = >29.5° = 29.5 + 23.5 = 53° S U N S Arctic U Sun overhead z = 0° Equator Capricorn N Sun on horizon z = 90° s

  24. WHAT IS ZENITH ANGLE AT SOUTHAMPTON? December 22 N Sun on horizon z = 90° S U N Z = >52° = 52 + 23.5 = 75.5° S Arctic U Sun overhead z = 0° Equator Capricorn N Sun on horizon z = 90° s

  25. WHAT IS ZENITH ANGLE AT PERTH, W.A.? December 22 N Sun on horizon z = 90° S U N S Arctic U Sun overhead z = 0° Equator Z = < 32° = 32 - 23.5 = 23.5° Capricorn N Sun on horizon z = 90° s

  26. BOTTOM LINE

  27. BOTTOM LINE March and September: Z at noon – Lat.

  28. BOTTOM LINE March and September: Z at noon = Lat. Summer (Jun. in N, Dec. in S): Z at noon = Lat -23.5°

  29. BOTTOM LINE March and September: Z at noon = Lat. Summer (Jun. in N, Dec. in S): Z at noon = Lat -23.5° Winter (Dec. in N, Jun. in S): Z at noon = Lat +23.5°

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