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Understanding Solar Radiation in Earth's Atmosphere

Explore how solar energy is absorbed, transferred, and affects the atmosphere's chemistry and dynamics. Learn about electromagnetic radiation, dissociation, energy thresholds, and the solar spectrum. Find lecture schedules, materials, and more on the course website.

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Understanding Solar Radiation in Earth's Atmosphere

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  1. METO 621 LESSON 1

  2. AOSC 621 - PHYSICS AND CHEMISTRY OF THE ATMOSPHERE II • Texts: Radiative Transfer in the Atmosphere and Ocean, Gary E. Thomas and Knut Stamnes, Cambridge University Press • Chemistry of Atmospheres, Richard P. Wayne, Oxford University Press • Lecturer: Professor Robert D. Hudson, Room 3421, • Computer and Space Sciences Building. • Phone 301-405-5394 • E-mail hudson@atmos.umd.edu • The Department of Meteorology Web Site is www.meto.umd.edu • Lessons           Tuesday 8.00 am to 9.15 am, in CSS 2428 •                         Thursday 8.00 am to 9.15 am in CSS 2428  • Office hours No set office hours will be posted. Students may come by my office at any time. • If you wish to make a formal appointment - send me an e-mail • ______________________________________________________________________________ • ______________________________________________________________________________  • The two textbooks listed above cover most of the material given in this course.. However, as AOSC 621 covers both chemistry and physics the course consists of selections from the textbooks. PowerPoint presentations have been prepared for each class, these will contain any material not covered by either book. .The .ppt files may be found on my web page: http://www.atmos.umd.edu/~hudson/meto621.d/ •             A schedule of the classes, homework assignments, etc can also be found on the same web site - AOSC621intr.htm . This schedule gives the material to be covered in each lecture. as well as the dates of the homework assignments . The homework assignments will be posted on my web site. In addition to the homework a project will be assigned at about mid-term.. There will be two exams, a mid-term exam and a final exam. 70% of the final grade will be based on these two exams, 15% on the project, and the remaining 15% on the homework assignments.

  3. Purpose • The purpose of this course is twofold: • (1) To examine how solar radiation is transferred through the atmosphere, absorbed by the Earth, and re-emitted by the Earth and atmosphere. • (2) To examine how this radiation drives the chemistry and dynamics of the atmosphere.

  4. Electromagnetic Radiation • Basically all of the energy that drives the chemistry and dynamics of the earth’s atmosphere emanates from the sun. • This energy is in the form of electromagnetic waves. • This is especially true if we consider the particles from the sun as having wave duality. • In order to explain the ejection of electrons from a surface illuminated with light, Einstein postulated that waves could be considered as a packet of particles each particle having an energy of h (where  is the frequency of the radiation). He called each particle a photon.

  5. Electromagnetic Radiation • By analogy a stream of particles can be considered as a wave. • The chemistry of the atmosphere is dominated by radicals derived from the dissociation of atmospheric species. • It is much easier to picture this dissociation as the interaction of a photon with a molecule than as an interaction of a wave with the molecular field. • Dissociation requires a threshold of energy, i.e. a certain frequency. Only photons with an energy (frequency) above this threshold will cause dissociation.

  6. Electromagnetic spectrum

  7. Electromagnetic spectrum • Most of the energy that drives the dynamics comes from a narrow band of frequencies known as the visible spectrum - heats the ground • Most the the energy that drives the chemistry pf the atmosphere comes from the ultraviolet part of the spectrum - high energy photons. • Most of the energy that heats the atmosphere is thermal radiation from the ground

  8. Schematic of a wave

  9. WAVELENGTH • DISTANCE BETWEEN SUCCESSIVE PEAKS • GIVEN THE SYMBOL λ • MANY UNITS USED : • (A) MICRON, 10-6 METERS • (B) NANOMETER, 10-9 METERS • (C) ANGSTROM, 10-10 METERS

  10. FREQUENCY

  11. VELOCITY • WAVE VELOCITY IS DEFINED AS THE DISTANCE A PEAK MOVES IN ONE SECOND. • IN VACUO THE WAVE VELOCITY OF AN ELECTROMAGNETIC WAVE IS 2.997925x108 METERS PER SECOND • FOR THOSE OF YOU WHO PREFER ENGLISH UNITS, THE VELOCITY OF LIGHT IS 1.80262x1012 FURLONGS PER FORTNIGHT. • THE WAVE VELOCITY IS GIVEN THE SYMBOL c.

  12. SOLAR ENERGY • Solar constant – energy from the sun that falls on unit surface normal to the line from the sun, per unit time, at the outside of the atmosphere at the mean solar distance S = 1.368 Kw per meter 2 • S is integrated over all wavelengths • S varies with the sunspot cycle

  13. SOLAR SPECTRUM

  14. SOLAR SPECTRUM • A blackbody curve for a temperature of 6000K matches the observed solar spectrum. • The difference between the 6000K spectrum below about 400 nm is due to absorption in the photosphere. • The structures shown below 400 nm are known as Fraunhoffer lines

  15. UV-VISIBLE SOLAR SPECTRUM OBSERVED FROM THE GROUND

  16. UV-VISIBLE SOLAR SPECTRUM OBSERVED FROM THE GROUND • Slide shows the absorption of the solar radiation by the atmosphere. • Major absorbers are molecular oxygen (O2), ozone (O3), water vapor (H2O) and carbon dioxide (CO2). • The wavelength is in nm. 1000nm is equal to one micron.

  17. SOLAR GEOMETRY

  18. EFFECTIVE AREA • If the solar zenith angle (SZA) of the sun is θ, then the effective area is given by 1/cos θ. • Hence the energy on unit area at the surface is S divided by the effective area, i.e. S.cos θ. • College Park is at a latitude of 39 degrees • At summer solstice the SZA is 17 degrees, and at the winter solstice 61 degrees • The ratio of the effective areas is 1.97, i.e. twice as much energy per unit area is incident on College Park at summer solstice than at winter solstice.

  19. INFRARED FLUX FROM EARTHSAHARA

  20. INFRARED FROM EARTHMEDITERRANEAN

  21. INFRARED FROM EARTHANTARCTIC

  22. HYDROSTATIC EQUATION Where H is called the atmospheric scale height

  23. HYDROSTATIC EQUATION-2

  24. HYDROSTATIC EQUATION-3 If we assume that g, T, and M* are constant then we get the equations

  25. Optical line-of-sight paths Note that the angle defined here is the polar angle

  26. Slant column mass

  27. Composition of the Earth’s Troposphere H2 PM O2 CH4 N2 CO N2O O3 ←SO2, NO2, CFC’s, etc Ar CO2 Inert gases

  28. Atmospheric composition

  29. Height profiles for minor species

  30. Height profiles for minor species • Species: Chlorofluorocarbons, CCl3F and CCL2F2 Nitrous oxide, N2O Methane, CH4 Nitric acid, HNO3 Carbon monoxide, CO Carbon dioxide, CO2. • Note that the CO2 line is vertical. This signifies that CO2 is well mixed in the atmosphere and has no significant chemical loss or production • The lines for the chlorofluorocarbons and nitrous oxide are vertical in the troposphere (well mixed) but suffer chemical loss in the stratosphere.

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