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Solar Radiation and the Seasons

A few considerations about the Sun. The Sun surface is extremely hot ~ 5800KThe electromagnetic energy is not depleted as it propagates towards the earthHowever as it moves away from the sun it is distributed over a greater area, which reduces its intensity (that is, the intensity of the solar r

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Solar Radiation and the Seasons

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    1. Solar Radiation and the Seasons 2) The causes of the Earth seasons

    2. A few considerations about the Sun The Sun surface is extremely hot ~ 5800K The electromagnetic energy is not depleted as it propagates towards the earth However as it moves away from the sun it is distributed over a greater area, which reduces its intensity (that is, the intensity of the solar radiation is less over Earth than it is over Mercury, for instance)

    4. Imagine a sphere completely surrounding the Sun whose radius is equal the mean distance Earth-Sun = 1.5x1011m

    5. FOR THE SAKE OF COMPARISON

    6. Causes of Earth’s Season interesting sites with movies: http://astro.unl.edu/naap/motion1/animations/seasons_ecliptic.swf http://www.youtube.com/watch?v=DuiQvPLWziQ

    7. So, what is the big deal about the solar constant? Well…solar variability has been considered, a priori, to be an external forcing factor for climate, although it remains a controversial mechanism of climate change, across all time scales. At times of high sunspot number, the value of the solar constant increases. Normally a change is less than 1% over the cycle. However, there have been periods in the past history of our planet when changes in the solar activity have been related to the decrease of temperature of our planet (such as the little ice age)

    8. So, what causes seasons!!!! Let’s think of an extreme example

    9. Imagine you living in Southern CA of this planet. ..

    12. And how would likely be the sunset in CA during summer…

    13. In summary The tilting of the axis of our planet is responsible for seasons Larger tilting – larger differences in seasons for higher latitudes

    14. Our actual planet – tilt of the axis : 23.5o

    15. Solar declination: the latitudinal position of the subsolar point: can be identified as the latitude at which the noontime Sun appears overhead

    16. Equinox

    17. NH summer solstice

    18. This is to have an idea how is the ‘sunset’ north of 66.5 during NH summer… (or south of -66.5 during SH summer)

    19. NH winter solstice

    20. In conclusion: The tilt of the Earth rotation axis influences the energy received on Earth by its effect on length of day and night So, in June all latitudes poleward of 66.5N (arctic circle) receives 24 hours of continuous daylight. Moving toward the equator the period of daylight decreases until reaching the equator where the daylight period is 12 hours. In December, poleward of 66.5N is 24 hours of continuous darkness

    22. Solar Elevation Angle

    23. This is because of the beam spreading

    26. Third way in which the tilt of the axis influences heating is in determining the amount of atmosphere that sunlight must penetrate before reaching surface

    27. Summary: What cause seasons?

    28. Quizzes for fun

    29. Quizzes for fun

    31. If you have curiosity to find more about astronomical theory for climate change you can check at (that are not in the text book) http://www.ncdc.noaa.gov/paleo/milankovitch.html

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