Global Energy Balance
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This document discusses energy pathways and balances at Earth's surface. It explains that 51% of incoming solar energy (insolation) is absorbed at the surface on average, while 29% is absorbed directly and 22% is absorbed after scattering. About 4% of insolation is reflected from the surface. The greenhouse effect occurs as the atmosphere absorbs and re-radiates heat, warming the planet. Urban areas experience higher temperatures than rural areas due to surfaces like asphalt and concrete that absorb and retain heat, creating urban heat islands.
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Global Energy Balance
- 1. Physical Geography GEOGRAPHY 1710 DAVID R. SALLEE
- 2. Chapter 4 Atmosphere & Surface Energy Balances
- 4. Energy Pathways Transmission – Passage of energy through atmosphere or water Scattering – Changing direction of light’s movement, without altering its wavelengths Refraction – Change in speed and direction of light
- 5. Refraction
- 6. Energy Principles Insolation input On a sunny day 75% of insolation may reach the earth’s surface; on an overcast day only 15%. On average 51% of insolation is absorbed by the surface as thermal energy – 29% as direct radiation and 22% as diffused radiation; i.e. scattered by atmospheric dust , water vapor and air molecules. Albedo About 4% of the radiation reaching the surface is directly reflected, at the same wavelength, from the surface back into space. Absorption Altogether some 70% of insolation is absorbed at the earth’s surface and in the upper atmosphere but eventually all this absorbed radiation is re-radiated back into space
- 8. Albedo Is the reflectivity of a surface.
- 10. Heat Transfer Conduction – Molecule to molecule transfer Convection – Energy transferred by movement Radiation – Energy traveling through air or space
- 11. Heat Transfer
- 12. The Greenhouse Effect and Atmospheric Warming Atmosphere absorbs heat energy A real greenhouse traps heat inside Atmosphere delays transfer of heat from Earth into space
- 15. Energy Balance at Earth’s Surface Daily Radiation Patterns Simplified Surface Energy Balance The Urban Environment
- 17. Urban Heat Islands -The consistently higher temperature found in cities as compared to rural areas • The air in an urban area can be as much as 20°F (11°C) higher than rural areas surrounding the city. • Urban surfaces of metal, glass, asphalt, concrete, and stone conduct up to three times more energy than wet sandy soil and are termed urban heat islands
- 19. URBAN HEAT ISLANDS Graphic courtesy of LLBL Heat Island Group
- 20. The image spans Salt Lake City on the western (l) edge of the image to the foothills of the Wasatch Mountains on the eastern (r) edge.
- 21. • The hard, dark surfaces like pavement store heat during the day, heat that is then released at night, keeping the city hotter for longer periods of time. • A growing percentage of Earth’s population live in urban areas. • Each person then experiences a unique set of altered microclimate effects: •*Increased conduction •*Lower albedos •*Higher NET R values •*Increased run-off *Complex radiation *Complex reflection *Anthropogenic heating *Pollution
- 22. GLOBAL URBANIZATION 80 70 World N. America Europe Russia M & S America Asia Africa Percentage 60 50 40 30 20 10 0 1950 1960 1970 1980 1990 2000 Urban Population as a Percentage of Total Population in Different Areas of the World, 1950-2000
- 23. Aerial thermal photograph of Sacramento showing cool areas and hot spots.
- 24. What is Albedo? • Reflectivity + Emissivity = Albedo • Reflectivity: the percentage of incident light or electromagnetic radiation that is reflected. • Emissivity: the rate at which absorbed energy is radiated from an object.
- 25. What can be done to reduce the Heat Island Effect? • Plant more canopy type trees • Use lighter colored materials for roads and parking lots • Use high Albedo materials