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

The Whole Picture

Source: www.noaa.gov

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.