{"id":127,"date":"2020-02-20T16:18:01","date_gmt":"2020-02-20T21:18:01","guid":{"rendered":"https:\/\/pressbooks.bccampus.ca\/earthsystems\/?post_type=chapter&p=127"},"modified":"2020-05-07T15:33:13","modified_gmt":"2020-05-07T19:33:13","slug":"chapter-4-2","status":"publish","type":"chapter","link":"https:\/\/pressbooks.bccampus.ca\/earthsystems\/chapter\/chapter-4-2\/","title":{"raw":"Chapter 3","rendered":"Chapter 3"},"content":{"raw":"

Topic 3 \u2013 Our Private Universe<\/span><\/strong><\/p>\r\nAveraged across the Earth, throughout the 24 hour day, the Sun delivers 340 watts\/m2 of radiation to the top of Earth\u2019s atmosphere. This constant supply of ready energy powers the critical zone of our planet in significant ways, including driving global circulation patterns in our atmosphere and oceans and providing the basis for photosynthesis and the production of biomass.\r\n\r\nWith respect to energy, the Earth is an open system. We receive energy from the Sun and we re-emit energy back to space. Energy contributed to the system by heat from the Earth\u2019s core represents a fairly small portion of this exchange, about 0.03%.\r\n\r\n[caption id=\"attachment_71\" align=\"aligncenter\" width=\"1024\"]\"Solar Incoming solar radiation is spread across the curved surface of the Earth, leading to differences in surface area for the same amount of radiation (the poles receive less intense radiation than the equator). The tilt of the Earth\u2019s axis, combined with its orbit around the sun lead to seasonal changes in the focus of the Sun\u2019s energy. Solstice points represent the longest and shortest daylight hours, whereas equinoxes represent equal daylight and night hours.[\/caption]\r\n\r\nThere are three basic controls on the delivery of this energy to the surface of the Earth:\r\n

    \r\n \t
  1. The spherical surface of the Earth results in different surface area exposed to the same incoming radiation.<\/li>\r\n \t
  2. The axial tilt of the Earth results in the same parts of the Earth alternatively pointing towards or away from the Sun during different parts of Earth\u2019s orbit around the Sun, and changes in the length of day throughout the year.<\/li>\r\n \t
  3. The rotation of the Earth on its axis results in daily changes in incoming solar radiation for a single location on the Earth\u2019s surface.<\/li>\r\n<\/ol>\r\n[caption id=\"attachment_133\" align=\"aligncenter\" width=\"300\"]\"A Earth's axial tilt[\/caption]\r\n\r\nTo look at how the orbital patterns and tilt change the Sun exposure for several locations on the Earth\u2019s surface throughout the year, check out the simulation here: https:\/\/sepuplhs.org\/middle\/iaes\/students\/simulations\/sepup_seasons5.html<\/a>\r\n\r\nThe angle at which the Sun\u2019s radiation encounters the top of the atmosphere and the Earth\u2019s surface is known as the [pb_glossary id=\"231\"]angle of incidence[\/pb_glossary]<\/strong> and is significant for two reasons:\r\n
      \r\n \t
    1. A steeper angle of incidence focuses solar radiation over a smaller surface area<\/li>\r\n \t
    2. A steeper angle of incidence reduces the amount of atmosphere through which the radiation has to travel before encountering the Earth\u2019s surfaceFor every latitude, the angle of incidence changes throughout the year with the seasons.<\/li>\r\n<\/ol>\r\nFor any given day of the year, the [pb_glossary id=\"232\"]latitude of the subsolar point[\/pb_glossary]<\/strong> is the latitude where the Sun is directly overhead (angle of incidence = 90\u00b0). At the equator at midday (noon), the Sun is directly overhead (angle of incidence of 90\u00b0) twice a year, during the equinoxes. On the June solstice, the Sun is directly overhead at the Tropic of Cancer (latitude 23.5\u00b0 N). On the December solstice, the Sun is directly overhead the Tropic of Capricorn (latitude 23.5\u00b0 S). On these days, at any other location on the Earth\u2019s surface, the angle of incidence will be <90\u00b0. You can calculate the local angle of the noon Sun<\/strong> (ANS), for any latitude on the Earth\u2019s surface on any day of the year using the Analemma and the following equation:\r\n

      ANS=90\u00b0-(Latitude \u00b1Latitude of the Subsolar Point)<\/em><\/p>\r\n\r\n