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Visible radiation violet 360 nm red 750 nm

Visible radiation violet 360 nm red 750 nm We ’ re most interested in the (visible) photosynthetically active radiation (PAR) Shortwave radiation is absorbed by water intensity decreases exponentially with depth. Spectra of downward radiation at different water depths

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Visible radiation violet 360 nm red 750 nm

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  1. Visible radiation • violet 360 nm • red 750 nm • We’re most interested in the (visible) photosynthetically active radiation (PAR) • Shortwave radiation is absorbed by water • intensity decreases exponentially with depth

  2. Spectra of downward radiation at different water depths Sea surface, 1 cm, and 1, 10, and 100 meters depth violet red

  3. Vertical profiles of radiation for selected wavelengths of light • infrared • red and blue visible, and • typical total shortwave

  4. Atmosphere-ocean heat exchange • Shortwave radiation warms the ocean • Ocean temperature is ~17oC or 290 K • Ocean emits radiation too, which cools it • Ocean radiates in the long-wave (infrared) wavelengths – why? • Long-wave is emitted only from the very surface of the ocean – why? • Downward long-wave arrives at the sea surface because of emission from water vapor in the atmosphere • (because of Wien’s Law)

  5. Atmosphere-ocean heat exchange • Sensible heat • Conduction • Depends on difference of air and sea temperature(can be warming, or cooling) • Exchange rate affected by wind speed • Latent heat • Evaporation (cools) • Depends on air relative humidity and saturation vapor pressure of moist air • Exchange rate affected by wind speed

  6. Calculating temperature increase in the mixed layer • Average summer day in North Atlantic at 40oN • Heat gain 500 W m-2 x 12 hours = 21,600 kJ m-2 • If the mixed layer is 5 m deep, about 76% is absorbed above 5 m depth = 17,100 kJ m-2 • Loss over same period ~ 10,400 kJ m-2 • Net energy gain during the day is Q = 6700 kJ m-2 • Temperature change is T = Q/(mass x specific heat) mass is density x volume = 1000 kg m-3 x 5 m3specific heat is 4.2 kJ kg-1oC-1 T = 6700/(5000 x 4.2) = 0.3oC increase in 1 day Box 3.01 in Mann and Lazier View live met data at http://mvcodata.whoi.edu/cgi-bin/mvco/mvco.cgi

  7. Solar heating is exponentially distributed with depth • Temperature profile is not exponential because turbulence stirs and mixes the water column • Mixing that entrains cool water from below the thermocline cools the mixed layer (dilutes with cold) • Zero net air-sea heat flux + plus mixing …gives net cooling

  8. Net Surface Radiation Why not maximum at the qauator? Why is local minimum off-set from the equator?

  9. Net surface thermal (long wave) radiation Why largest (most negative) over continents? Why spatial variability over continents?

  10. Net surface heat exchange--- note that there is a loss of heat throughout the Entire North Atlantic! But not in North Pacific.

  11. Svante Arrhenius. The large picture shows him in Spitsbergen, Norway, seeing off an Arctic balloon expedition in 1896. In 1896, when he published his greenhouse calculation, Arrhenius was Professor of Physics and Rector at the Stockholm Högskola. He was already famous for showing how dissolved salts separate into charged particles ("ions"). In 1903 he was awarded the Nobel Prize in Chemistry for "the extraordinary services he has rendered to the advancement of chemistry by his electrolytic theory of dissociation.

  12. New York Times 1890

  13. Increase in total radiative forcing To earth’s ~ 2 W/m2

  14. Figure 5.14 Changes in solar constant (total solar irradiance) and global mean temperature of Earth’s surface over the past 400 years. Except for a period of enhanced volcanic activity in the early 19th century, surface temperature is well correlated with solar variability. From Lean, personal communication.

  15. Note that heat transport in Atlantic extends further north than Pacific.

  16. Figure 5.14 Changes in solar constant (total solar irradiance) and global mean temperature of Earth’s surface over the past 400 years. Except for a period of enhanced volcanic activity in the early 19th century, surface temperature is well correlated with solar variability. From Lean, personal communication.

  17. Some radiation physics • Incoming radiation from the sun is in the shortwave band(wavelengths of 280 nm to 2800 nm) • Wavelength of emitted radiation depends on the “black-body” temperature (Wien’s Law) Lmax= c/Tkwhere c = 2.9 x106 nm K • Our Sun is 5800 K • Ultraviolet 300 nm to far infrared 2400 nm • Averaged over the Earth we receive about 340 W/m2 at the top of the atmosphere Wilhelm Carl Werner Otto Fritz Franz Wien

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