Lecture notes on Atmospheric Physics

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Lecture Atmospheric Physics University of Bremen Master of Environmental Physics WS 2003 / 2004 Andreas Richter room U2090, tel. 4474 richteriup.physik.uni-bremen.de Tutorial: Oluyemi Afe room U2080, tel. 7421 afeiup.physik.uni-bremen.de Contents: 1. Survey of the Atmosphere 2. Radiation in the Atmosphere 3. Climate Change 4. Atmospheric Thermodynamics and the role of Water Vapour 5. Introduction to Dynamics of the Atmosphere Atmospheric Physics - 2 - University of Bremen, WS 2003 / 2004 Disclaimer This file contains the lecture notes for the Atmospheric Physics lecture given at the University Bremen during the winter term 2003 / 2004. This is not a book, and much of the information given in the lecture is missing. Also, many figures and explanations were taken from books, articles and web pages without proper reference. In particular, many parts are based on the script by K. Künzi and S. Bühler. The contents of this file may therefore used only for educational purposes. There probably are errors, omissions, inconsistencies and confusing explanations in these lecture notes. If you find any of these, please send an email to Andreas.Richteriup.physik.uni-bremen.de Atmospheric Physics - 3 - University of Bremen, WS 2003 / 2004 The Rules of the Game: Lectures: • 13 lectures, every Wednesday • one “rapporteur” gives brief summary from last lecture Exercises: • 10 exercises • will be distributed in the lecture • will have to be submitted on the next Tuesday (6 days to work on it...) • no copies, joined solutions, cryptic notes please • will be returned and discussed on the next day in the tutorial after the lecture • credits: 10 x 10 = 100 Exam: • prerequisite to take part in the exam: o at least 75 credits from exercises o acted at least once as rapporteur • 2 hours written exam in the first or second week after the end of lectures Atmospheric Physics - 4 - University of Bremen, WS 2003 / 2004 Literature for the Lecture English Books: Houghton, J.T., The physics of atmospheres, Cambridge University Press, 1977, ISBN 0 521 29656 0 Wallace, John M. and Peter V. Hobbs, Atmospheric Science, Academic Press, 1977, ISBN 0-12-732950-1 Deutsche Bücher: Roedel, Walter, Physik unserer Umwelt, Die Atmosphäre, Springer Verlag, 1992, ISBN 3-540- 54285-X Script: Environmental Physics I, WS 2002/2003, Klaus Künzi and Stefan Bühler, Institute of Environmental Physics, University of Bremen, Bremen; Germany Atmospheric Physics - 5 - University of Bremen, WS 2003 / 2004 Schematic Overview Cosmic Radiation Sun Extraterrestrial Effects Radiation Absorption and Emission Green House Water Chemistry Thermodynamics Photolysis Clouds Trace Species Precipitation (special course) Stability Dynamics Earth surface: Land, Orography, Albedo, Ocean and Ocean Dynamics Atmospheric Physics - 6 - University of Bremen, WS 2003 / 2004 Atmospheric Composition Today Molecular Content Constituent Weight (fraction of g / mol molecules) Nitrogen (N) 28.016 0.7808 2 Oxygen (O) 32.00 0.2095 2 Argon (Ar) 39.94 0.0093 Water vapour (H O) 18.02 0 - 0.04 2 Carbon Dioxide (CO) 44.01 325 ppm 2 Neon (Ne) 20.18 18 ppm Helium (He) 4.00 5 ppm Krypton (Kr) 83.7 1 ppm Hydrogen (H) 2.02 0.5 ppm 2 Ozone (O ) 48.00 0 - 12 ppm 3 • most constituents are very stable in concentrations • exception: H O and O that vary rapidly in 2 3 space and time and CO , that increases slowly 2 as a result of anthropogenic emissions • many other trace gases are present in the atmosphere however in small and variable concentrations Atmospheric Physics - 7 - University of Bremen, WS 2003 / 2004 Planetary Atmospheres Surface Pressur Gravitatio Temperatur e Plane Compositio n e at Surface 3 t n 10 (relative) K hPa Venu 0.91 700 100 CO 90% 2 s N 2 Earth 1 290 1 ( 78 %) O 2 ( 21 %) CO 2 Mars 0.38 210 0.01 ( 80 %) • Earth’s atmosphere is unique in pressure, temperature and atmospheric composition Atmospheric Physics - 8 - University of Bremen, WS 2003 / 2004 Origin of the Atmosphere 9 • at the time of formation (4.5 x 10 years ago), earth had no or little atmosphere • the atmosphere was formed from volatile emissions from the interior of the earth (volcanic activity) • volcanic emissions are roughly 85% H O, 10% 2 CO , and a few per cent sulphur compounds 2 Questions: • where is the CO ? 2 o in carbonates in the earth’s crust • where is the H O? 2 o deep ocean leakage o photodissociation? • where is the O coming from? 2 o photodissociation 2H O + hν → 2H + O 2 2 2 o photosynthesis H O + CO→ CH O + O 2 2 2 2 • where is the N coming from? 2 • where are the noble gases coming from? o radioactive decay Atmospheric Physics - 9 - University of Bremen, WS 2003 / 2004 The Carbon Budget • in photosynthesis, carbon is incorporated into organic compounds • a small part of this organic matter is not oxidized, but fossilized in shales or fossil fuels • 90% of the O produced by photosynthesis is 2 stored in the earth’s crust in oxides such as FeO or carbonate compounds such as 3 CaCO Fe O , or MgCO 3, 2 3 3 • the carbonates are the main sink of atmospheric CO 2 Substance Fraction % Rocks 71 Shales 29 Ocean, dissolved CO 0.1 2 Oil, gas, coal 0.03 Atmosphere (CO) 0.003 2 -5 Biosphere 7x10 Atmospheric Physics - 10 - University of Bremen, WS 2003 / 2004 Inputs / Outputs to the Atmosphere • Input from volcanic activity • Input from meteorites • Exchange with Biosphere • Exchange with Hydrosphere • Loss to outer space and earth Atmospheric Physics - 11 - University of Bremen, WS 2003 / 2004 Impact of Biosphere • The Earth’s atmosphere is far away from the equilibrium expected for a planet without life. • The disequilibrium is sustained by permanent emissions and adsorptions of species by the biosphere. • Many feedback mechanisms are known through which the atmosphere is kept in its current state (CO from weathering of silicate 2 rocks by soil bacteria, cloud nucleation from DMS emitted from the oceans, ozone layer, ...) • Provokingly, the atmosphere can be seen as part of the biosphere (Gaia hypothesis) Atmospheric Physics - 12 - University of Bremen, WS 2003 / 2004 Anthropogenic Impacts Humankind is changing atmospheric composition by • emissions of particulates (20% of total) • burning of fossil fuels which has a direct impact on CO concentrations (1000 years of 2 photolysis undone per year) • emissions of trace species that alter atmospheric chemistry in many ways • emission of trace species that alter the radiative properties of the atmosphere directly or indirectly (cloud formation or change) • direct or indirect changes of temperature Atmospheric Physics - 13 - University of Bremen, WS 2003 / 2004 Role of Water in the Atmosphere Water in the atmosphere is of particular importance as • concentration varies strongly with height, location, temperature,... • it is present in all three phases (solid, liquid, gaseous) in the atmosphere and the hydrosphere in general • condensation and evaporation is connected with large changes in latent heat that are crucial for energy transport in the atmosphere, and are the driver for atmospheric dynamics • water vapour concentration determines the vertical profile of temperature in the atmosphere • rain is essential for the removal of particles and many gases from the atmosphere • it is playing an important role in the greenhouse effect Atmospheric Physics - 14 - University of Bremen, WS 2003 / 2004 Water Vapour in Atmospheres T K Vapor Venus Liquid Water Earth Ice Mars -1 -1 Water Vapor Pressure 10 Nm • Earth is the only planet in the solar system where water can exist in all three phases. • Most of the water emitted by volcanoes in Earth’s history is missing (99%) • Only a very small fraction of the water is in the atmosphere (97% in oceans, 2.4% in ice, 0.6% in underground fresh water, 0.02% in lakes and rivers, and 0.001% the atmosphere) Atmospheric Physics - 15 - University of Bremen, WS 2003 / 2004 The Atmosphere in Perspective The atmosphere • is exceedingly thin • contains only a minute fraction of the Earth’s mass (0.025%), even for its main constituents • Lithosphere (the earth’s crust), Hydrosphere (water on or above the earth’s surface) and Biosphere (all animal and plant life) act as huge reservoirs for atmospheric constituents Atmospheric Physics - 16 - University of Bremen, WS 2003 / 2004 Vertical Structure of the Atmosphere Atmospheric Physics - 17 - University of Bremen, WS 2003 / 2004 Vertical Structure of the Atmosphere Classification according to T-profile: • Troposphere • Stratosphere • Mesosphere • Thermosphere • Exosphere Boundaries between layers are called “-pause”; most important here: the tropopause Tropopause varies with season, latitude, temperature and pressure systems Different tropopause definitions based on T, O , 3 potential temperature, H O, or combinations of the 2 above. Classification according to mixing: • Homosphere • Heterosphere Atmospheric Physics - 18 - University of Bremen, WS 2003 / 2004 Vertical Structure of the Atmosphere Reasons for the temperature profile: • adiabatic vertical transport • radiative cooling by water vapour • absorption in the ozone layer • oxygen absorption in the thermosphere Consequences of the temperature profile: • strong mixing in the troposphere • low vertical mixing in the stratosphere • very low humidity in the stratosphere (tropopause acts as a cooling trap) • troposphere and stratosphere are largely separated regions of the atmosphere, and exchange between the two is limited to specific regions: o through convection in the tropics o in tropopause folds o through subsidence in polar regions Atmospheric Physics - 19 - University of Bremen, WS 2003 / 2004 Abundance Units in Atmospheric Science quantity symbol units 23 number of N mol = 6.022 x10 molecules 3 number density n particles / m 3 mass density kg / m ρ -6 volume ppmV = 10 µ -9 mixing ratio ppbV = 10 -12 pptV = 10 -6 mass ppmm =10 µ -9 mixing ratio ppbm =10 -12 pptm = 10 2 column molec/cm abundance or DU -3 = 10 cm at STP Atmospheric Physics - 20 - University of Bremen, WS 2003 / 2004 Ideal Gas Assumptions: • ensemble of individual molecules • no interaction apart from collision • no chemical reactions • no appreciable volume of individual molecules State properties of a gas: p, T, V, and n Equation of state for the ideal gas: pV= nRT or pV= NkT p = pressure, V = volume, n = number of moles, N = number of molecules, R = universal gas constant, k = Boltzman constant, T = temperature All gases act as ideal gases at very low pressure; to good approximation, gases in the atmosphere can be treated as ideal gases with the exception of water vapour (phase changes)