Ocean and SunAP Env Sci 2011-2012
Global Winds and Ocean Currents
The source of this material is the Digital Library for Earth System Education website at http://www.dlese.org.
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Source: NOAA
The Gulf Stream
Source: NASA
The Gulf Stream
• East Coast United States, officially discovered by Benjamin Franklin, mapped and published in 1770
• Strengthened and directed by the Westerlies
• Moves North and East– North Atlantic Drift: Keeps Britain and NE
Europe warmer than predicted by latitude.
Thermohaline Circulation
• Thermo = temperature• Haline = salinity
• Colder, higher salinity water sinks (more dense)
Source: NOAA
Why are Ocean Currents Important?
• Navigation
• Moderating Climates (ie., Great Britain)
• Maintain Earth’s Heat Balance– Move heat from Tropics to Poles– About ¼ of Earth’s total heat movement
Upwelling and El Nino
• http://www.youtube.com/watch?v=uySu7Zv2cbU
• http://www.montereyinstitute.org/noaa/lesson08.html
Sun – The Source of Earth’s Energy
• What Happens to the Incoming Energy?
Source: www.noaa.gov
Fate of Incoming Solar Energy
Reflected: 31% of TotalScattered Into Space by Atmosphere: 8%Reflected by Clouds: 17%Reflected by Earth’s Surface: 6%
Absorbed: 69% of TotalAbsorbed by Gases (water vapor, dust, ozone) 19%Absorbed by Clouds 4%Absorbed by Earth’s Surface 46%
What Determines Whether Energy is Reflected or Absorbed?Wavelength!
• “Short” wavelength radiation (0.3 to 0.7 um wavelength) makes up a large fraction of Sun’s radiation.
• This energy passes readily through the Atmosphere.
• This is visible light
• Major absorber @ UV (short) wavelength:• Oxygen/Ozone 0.2-2 um • Not Nitrogen
Source: NOAA
Reflectivity of Earth’s Surfaces
• Albedo: Fraction of total radiation reflected by a surface.
• Average for Earth (solid, liquid, gas) is about 30%
Surface Percent Reflected
Fresh snow 80-85
Old snow 50-60
Sand 20-30
Grass 20-25
Dry earth 15-25
Wet earth 10
Forest 5-10
Water (Sun low) 50-80
Water (Sun high)
3-5
Thick cloud 70-80
Thin cloud 25-30
Fate of Radiation Absorbed by Surface
• About 50% of total energy from Sun is absorbed – this must be “lost” or Earth will HEAT UP!
• Where it goes:– About 7% heat transported from Earth’s
surface to atmosphere by conduction and convection
– About 23% heat transported upward by evaporation
– About 21% lost by long wavelength (IR) radiation from Earth’s surface
• All of this is eventually lost to space by long wavelength (IR) radiation from atmosphere
Greenhouse Gas Intro
• On previous slide, long wavelength energy (IR/heat) is transferred from Earth to atmosphere.
• We learned that UV/visible light is absorbed by O2/O3
• Greenhouse gases absorb long wavelength (IR) energy and re-radiate some back to Earth’s surface.
• Some heat is “trapped” in the troposphere and Earth’s surface.
• Aside: Interestingly, although this is called the “Greenhouse Effect” it is not actually how greenhouses work.
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