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The Atmosphere

The Atmosphere

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The Atmosphere

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  1. The Atmosphere It appears that approximately an inch (2.5 cm) of ice is coating this hapless tree. The icy fangs are an indication that melt is underway. Typically, a quarter inch (0.65 cm) of ice is all that’s needed for tree branches to begin to snap.

  2. Frequency, Wavelengths & Energy of Photons Energy emitted from the sun (i.e electromagnetic radiation exhibits both a wave-like (electromagnetic wave) and a particle-like (photon) nature.

  3. Duality of light and matter In 1690 Christiaan Huygens theorized that light was composed of waves, while in 17-4 Isaac Newton explained that light was made of particles. Experiments supported each of their theories. However neither a completely-particle theory nor a completely-waver theory could explain all of the phenomena associated with light. So how can something be both a particle and a wave at the same time? The wave of light is simply the probability of where the particle will be. Let’s hear a little quantum physics explained.

  4. Energy in the form of photons is absorbed or emitted as electrons change energy levels within the structure of an atom. Photon = A particle-like unit of electromagnetic energy (light) emitted or absorbed by an atom when an electrically charged electron changes state.

  5. Recall that Photons are energy packets having a well-defined wavelength and frequency.

  6. An electron in its ground state about to absorb a photon The electron leaps to a higher level as the photon is absorbed.

  7. As an electron emits or “gives off” electromagnetic energy (in the form of a photon), it jumps from a Higher to a Lower energy state (level).

  8. An electron in its excited or quantized state. The electron leaps to a lower energy level and a photon is emitted.

  9. Summary of quantum mechanics & the link to absorption of electromagnetic energy at the subatomic scale. If a photon of electromagnetic energy strikes an atom, And if the Frequency of the electromagnetic radiation is such that it is equal to the difference in energy of the ground level & the first excited level, The electron Absorbs the photon energy and…. The electron is “moved” (quantum leap) to “Level 2”

  10. Quantum behavior of Molecules Quantum theory also involved the behavior of molecules: the molecular-scale motion (I.e. rotation, bending, & vibration) of molecules. Molecular motions in the gases Water Vapour andCarbon Dioxide (H2O and CO2) explain why some gases contribute to the greenhouse effect and others do not.

  11. Both Sun & Earth are radiating energy… …At different electromagnetic wavelengths ….and at different frequencies

  12. Wavelengths

  13. Quantifying Frequency & Wavelengths First we’ll talk about the WAVE-like behavior of electromagnetic energy: Wavelength = the distance between adjacent crests (or troughs) (symbol = lambda ) Frequency = how fast the crests move up and down (symbol = nu ) Speed = how fast the crests move forward (symbol = c) the speed of light

  14. The pattern of wavelengths absorbed by a particular atom or combination of atoms, (e.g. a gas molecule of CO2 or H2O) Is called its Absorption Spectrum or its absorption curve

  15. Solar Radiation greatest intensity in SHORT wavelengths (high energy & frequency) Earth (terrestrial) Radiation entirely in LONG wavelengths (low energy & frequency)

  16. Quantum behavior of Molecules Quantum theory also involved the behavior of molecules: the molecular-scale motion (I.e. rotation, bending, & vibration) of molecules. Molecular motions in the gases Water Vapour andCarbon Dioxide (H2O and CO2) explain why some gases contribute to the greenhouse effect and others do not.

  17. Nitrogen Gas Molecule N2 Water Molecule H2O Carbon Dioxide Molecule CO2

  18. Nitrogen Gas Molecule N2 Not a Greenhouse Gas Water Molecule H2O Greenhouse Gases Carbon Dioxide Molecule CO2

  19. When the H2O molecule emits a photon its rotation rate decreases. When it absorbs a photon, the rotation rate increases.

  20. Molecules can also absorb and emit IR radiation by changing the amplitude with which they vibrate. If the frequency at which a molecule vibrates matches the frequency of an electromagnetic wave, the molecule can absorb a photon and begin to vibrate more vigorously.

  21. As a triatomic molecule, one way that CO2 vibrates is in a “bending mode”that has a frequency that allows CO2 to absorb IR radiation at a wavelength of about 15 micrometers. Another triatomic molecule: N2O does the same thing.

  22. Dance your PhD N2O acts as a greenhouse gas through the absorption of radiation in 3 vibrational modes. With one hand as a nitrogen atom, torso as central nitrogen, and the other hand as an oxygen atom, the dancers exhibit the three specific movements of N2O’s vibrational modes as it moves from soil to atmosphere. http://www.youtube.com/watch?v=L5j6BS3XoLc

  23. The N2O starts in the soil where it is produced by microbial activity and “moves on up” into the atmosphere. Stepping onto the chairs represents the progression of N2O to higher levels in the atmosphere (the stratosphere) where it is subject to intense Ultraviolet UV radiation from the sun. This high energy from the bombarding UV radiation is shown in the dancers’ high energy, more spastic dancing. The high intenesity UV radiation leads to the destruction of N2O --Jumping from the chair.

  24. We will learn later that interaction of N2O in the stratosphere with UV wavelengths is related to Ozone Depletion …but N2O also vibrates & bends when absorbing Infrared (IR) wavelengths …it is the ability to absorb and emit IR radiation that makes N2O a GREENHOUSE GAS

  25. What defines a GREENHOUSE GAS? Abbreviation we’ll use = GHG GHG = a gas that can absorb and emit (re-radiate) Infrared wavelengths of Electromagnetic Radiation

  26. The Quantum Behavior of certain molecules with respect to Infrared radiation is the reason that Greenhouse Gases are Greenhouse Gases.

  27. Longwaves (LW) Shortwaves (SW)

  28. Key bands in the spectrum for Global Change: UV, Visible, IR, NIR

  29. Definition of Greenhouse Gases Greenhouse gases are gases which both absorb and emit electromagnetic radiation in the infrared (IR) part of the spectrum. Once IR is absorbed by the greenhouse gases in the atmosphere, it can be emitted back to the Earth’s surface to heat it all over again. Or it can be emitted upward to outer space and be lost from the system altogether.

  30. IR radiation is emitted fro the Earth’s surface right out to space through “IR window” IR radiation is absorbed by GH gases in the atmosphere and emitted out to space IR radiation is absorbed by GH gases in the atmosphere and emitted back to Earth.

  31. Different gases absorb & emit radiation at different wavelengths How do we know which wavelengths are absorbed/emitted by different gases?

  32. The pattern of electromagnetic wavelengths that are absorbed & emitted by a particular atom (or combination of atoms) Is called its Absorption Spectrum or Absorption Curve

  33. Match the gas with its absorption curve. Choices: H2O O2/O3 N2O CH4 CO2

  34. Match the gas with its absorption curve. Choices: H2O O2/O3 N2O CH4 CO2

  35. Choices: H2O O2/O3 N2O CO2 ???

  36. Key concepts to get out of all of this: Solar radiation is mostly in shortwave (SW) form (visible and UV). Most visible and UV wavelengths are transmitted through the atmosphere but some (esp. harmful UV) are absorbed on their way to Earth’s surface by O2 and O3.

  37. 2. Most of the incoming solar energy absorbed by the Earth and the atmosphere is absorbed at the Earth’s Surface which then radiates IR outward to heat up the atmospehre. Hence, the Atmosphere is heated primarily from below

  38. 3. Terrestrial radiation is mostly in longwave (LW) form (IR). Much of the outgoing terrestrial radiation is absorbed by H2O and CO2 (and other GHG’s) before it escapes to space, and it is re-radiated back to the Earth’s surface. This is the “Greenhouse Effect”

  39. 4. The re-radiation of LW (IR) energy to the Earth’s surface by GH gases is what keeps the Earth in the “just right” temperature range for water to be present in all 3 phases and just right for US. Without the “Greenhouse Effect” the Earth would be too COLD for life as we know it!

  40. Objectives: To understand: The vertical structure of the atmosphere & its relationship to temperature Which gases are in the atmosphere where they are concentrated Why gases at different levels are linked to the greenhouse effect & ozone depletion

  41. http://earthguide.ucsd.edu/earthguide/diagrams/atmosphere/index.htmlhttp://earthguide.ucsd.edu/earthguide/diagrams/atmosphere/index.html

  42. The Vertical Structure of the Atmosphere Key Concept: The atmosphere’s vertical structure is defined by changes in the trend of temperature with height