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Physics of the Atmosphere Physik der Atmosphäre

Physics of the Atmosphere Physik der Atmosphäre. SS 2010 Ulrich Platt Institut f. Umweltphysik R. 424 Ulrich.Platt@iup.uni-heidelberg.de. Physics of the Atmosphere MVEnv1. Prerequisits: Masters Course experimental Physics: Environmental Physics (MKEP4) or equivalent.

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Physics of the Atmosphere Physik der Atmosphäre

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  1. Physics of the Atmosphere Physik der Atmosphäre SS 2010 Ulrich Platt Institut f. Umweltphysik R. 424 Ulrich.Platt@iup.uni-heidelberg.de

  2. Physics of the Atmosphere MVEnv1 • Prerequisits: Masters Course experimental Physics:Environmental Physics (MKEP4) or equivalent. • Physics of the Atmosphere (this lecture): • (Thermo-)dynamics of the atmosphere • Radiation • Global atmospheric circulation • Diffusion and turbulence (advanced topics) • Atmospheric chemistry • Global cycles of atmospheric constitutents • Aerosols • Isotopes in atmospheric physics and chemistry • Measurement techniques

  3. Contents

  4. Literature (IUP xxxx: Book - Nr. in the library of the Institut für Umweltphysik, INF 229, 4th floor, R.410) • Physik unserer Umwelt, Die Atmosphäre, Walter Roedel, Springer, Heidelberg, 3. Aufl., Eine ausgezeichnete Übersicht der physikalischen Prozesse in der Atmosphäre (IUP 1511). • The Physics of Atmospheres, J. T. Houghton, Cambridge University Press, Cambridge 3rd Edition, 2002. Good, concise introduction. • Atmosphere Chemistry and Physics, J.H. Seinfeld und S.N. Pandis, John Wiley & Sons, New York, 1998. Very comprehensive book on physics and chemistry of troposphere and stratosphere (IUP 1724). • Theoretische Meteorologie, Eine Einführung, Dieter Etling, Springer Verlag Heidelberg, 2nd ed., 2002, ausführliche Einführung in Dynamik (UB LN-W 23-8691). • Fundamentals of Atmospheric Physics, M. L. Salby, Academic Press, 1996: Failry comprehensive introduction to all aspects of atmospheric physics (IUP 1647). • Aeronomy of the Middle Atmosphere, 2nd edition, G. P. Brasseur and S. Solomon, 2005 (IUP 1211). • Fundamentals of Physics and Chemistry of the Atmosphere, G. Visconti, Springer-Verlag, 2001; Good and concise text, sometimes surprising mistakes. • Fundamentals of Atmospheric Modeling, M. Z. Jacobson, Cambridge University Press, 2005; Covers physics and chemistry of troposphere and stratosphere with the goal to provide the relevant equations for numerical modeling. (IUP 1925) • Physics of Climate, J. P. Peixoto, A. H. Oort, American Inst. of Physics, 1992; Dynamics, radiation, thermodynamics and a lot of observational data on climate (IUP 1409).

  5. Lecture notes http://www.iup.uni-heidelberg.de/institut/studium/lehre/Atmosphaerenphysik/

  6. Web Sites of Interest (1) Intergovernmental Panel on Climate Change (IPCC) http://www.ipcc.ch/Presents the comprehensive reports (presently 4th report of 2007) of an international, independent group of scientists on climate and climate change. European Ozone Research Coordinating Unit http://www.ozone-sec.ch.cam.ac.uk/Results of European research on stratospheric chemistry and ozone loss. NASA Life on Earth http://www.nasa.gov/vision/earth/features/index.htmlComprehensive site centred on remote sensing of planet earth. German Weather Service (Deutscher Wetterdienst) http://www.dwd.de/en/en.htmInformation on weather and climate National Oceanic and Atmospheric Administration (NOAA) http://www.noaa.gov/ The Federal Environmental Agency (Umweltbundesamt) http://www.umweltbundesamt.de/index-e.htmHas much information on the state of the environment in Germany. IGBP - International Geosphere-Biosphere Programme http://www.igbp.kva.se/cgi-bin/php/frameset.phpMission: Deliver scientific knowledge to help human societies develop in harmony with Earth’s environment. Institute for Environmental Physics - Institut für Umweltphysikhttp://www.iup.uni-heidelberg.de Our own web-page Marsilius Kolleg, University of heidelberghttp://www.marsilius-kolleg.uni-heidelberg.de/projekte/climate_engineering.html

  7. Web Sites of Interest (2) - References Journal of Atmospheric Chemistry and Physics, http://www.copernicus.org/EGS/acpThis journal comes in two versions:1) JACP – Discussion 2) JAPC The reviewed journalboth are completely in the internet and freely available “The Master Chemical Mechanism” http://www.chem.leeds.ac.uk/Atmospheric/MCM/mcmproj.html JPL-Compilation: “Chemical Kinetics and Photochemical Data for Use in Stratospheric Modelling” http://jpldataeval.jpl.nasa.gov/ NIST-Compilation: http://kinetics.nist.gov/index.php IUPAC-Compilation: http://www.iupac-kinetic.ch.cam.ac.uk/ NASA’s “Visible Earth” http://visibleearth.nasa.gov Aerosol Inorganic Modelling Home Page: http://www.hpc1.uea.ac.uk/~e770/aim.html

  8. Outline for Today • Atmospheric physics – a definition • Earth System Science • Important features of the Earth’s atmosphere • Spatial and temporal scales in the Earth’s atmosphere • Some dynamical features • Energy • Composition and history of the atmosphere • Hydrostatic equation

  9. There are many clouds the Earth is blue/bluish.. The Earth from space First picture of the Earth The atmosphere is thin

  10. Atmospheric Physics – a Definition • Atmosphere - (greek ατμός, atmós „air, pressure, vapour“ und σφαίρα, sfära „sphere“) is the gaseous envelope of a celestial body that is confined due to gravitational attraction. • Physics of the atmosphere is the study of all physical phenomena in/of an atmospheric system. • Also: • Meteorology • Atmospheric chemistry • Atmospheric science

  11. Earth System Sciences IPCC, 2001

  12. Masses of Environmental Compartments • Atmosphere: 5.3 1021 g • Biosphere: 1.3 1021 g • Hydrosphere: 1.4 1024 g • Earth: 6.0 1027 g All Water on Earth R700km All Air on Earth: Sphere R1000km 1.41 Mrd. km3 (standard conditions) Source: Adam Nieman, http://www.adamnieman.co.uk/vos/index.html

  13. The Role of Physics in Atmospheric Sciences • Thermodynamics • Phase transitions - condensation and evaporation • Adiabatic processes, temperature & pressure gradients • Quantum Mechanics • Interaction of radiation & matter • Chemical processes • Hydrodynamics • Navier-Stokes equation • Classical mechanics • Rotating inertial systems, Coriolis and centripetal forces • Transport Phenomena • Turbulence • Diffusion

  14. The Atmosphere • The atmosphere is a vital part of our environment: • provides protective layer for life (stratospheric O3) • atmospheric compounds are essential for metabolism (e.g. O2, CO2) • is part (compartment) of the Earth system • connects different compartments & is driving force in climate system • determines cycling of energy and matter • is a complex dynamical system (chaotic motion) • is a very thin & extended layer (7-8 km at surface pressure)

  15. Example for physical processes in the atmosphere:Formation of a convective cloud Heating of surface due to absorption of solar radiation Addition of sensible and latent heat as well as moisture to surface air Expansion of air, reduction of density, convective rising of air parcel Adiabatic expansion, to the expense of internal energy  cooling

  16. H2O partial pressure exceeds H2O saturation pressure  condensation Release of latent heat  stronger convection, formation of circulation systems (subsidence) Growth of droplets (condensation, collision – coalescence), scavenging of aerosol particles and gases, precipitation, cloud chemistry Increase of planetary albedo due to clouds  reduction of incoming solar radiation  cooling Depending on cloud height: increase of greenhouseeffect due to scattering of long-wave radiation by clouds

  17. Ionosphere Heterosphere Neutrosphere Homosphere Vertical extent of the atmosphere Barry+Chornley, fig 1.15

  18. Time and Length Scales of Dynamical Processes in the Atmosphere Kraus, Fig 1.5

  19. Characteristic transport times Jacobson et al., 2000 Jacob, 1999

  20. name chemical formula relative abundance [%] nitrogen N2 77.9 oxygen O2 20.95 argon Ar 0.93 carbon dioxide CO2 0.036 neon Ne 0.0018 helium He 0.0005 water vapour H2O 10-5 - 4 methane CH4 0.00017 krypton Kr 0.00011 hydrogen H2 0.00005 ozone O3 1  10-6 - 1  10-3 Composition of the Atmosphere Nitrogen N2: MN2 = 28,015 kg kmol-1 Oxygen O2: MO2 = 31,999 kg kmol-1 Argon Ar: MAr = 39,942 kg kmol-1 Carbon dioxide CO2: MCO2 = 44,008 kg kmol-1

  21. 1 10-3 10-9 10-6 10-12 N2 O2 Xe Kr He Ne Ar Noble gases H2O CO2 CH4 H2 CO O3 Hydrocarbons NOX SO2 HO2 4-5 4-100‘s 5-6 ?? 100‘s-1000‘s OH ppb ppt ppm No. of different spezies Mixing Ratios of Atmospheric Trace Gases

  22. Mixing Ratio Moles/Mole, ppm Altitude, km Concentration, Molecules/cm3 The Stratospheric Ozone Layer, Where is the Maximum?

  23. Which Units ? 1) Concentration Where ‘amount’ refers to either mass (cm), number of molecules (cn), or number of moles (cM). Examples for units of concentration:micrograms per m3 or molecules per cm3 (‘number density’ of a gas).The partial pressure of a species is also a measure of its concentration. 2) Mixing ratio Examples:

  24. Conversion of Units For standard conditions (p0 = 101325 Pa = 1 Atmosphere, T = 273.15 K) the molar volume is V0 = 22414.00 cm3/mole. For arbitrary temperature and pressure conditions we can use: Mean molar mass of the (dry) homosphere: 28.965 Kg/KMole

  25. Noble gases N2 O2, Micro Scale Urban or Local Scale Regional or Mesoscale Synoptic or Global Scale CFC’s Long-Lived Species N2O CH4 Inter-Hemispheric Mixing Time CH3CCl3 CH3Br Moderately Long-Lived Species CO Intraemispheric Mixing Time Trop O3 Aerosols 1s 100s 1hr 1 day 10 days 1yr 10 yrs 100 yrs SO2 H2O2 NOx DMS C3H6 Boundary Layer Mixing Time C5H8 Short-Lived Species CH3O2 HO2 NO3 OH 1m 10m 100m 1km 10km 100km 1000km 10,000km SPATIAL SCALE TIME SCALE Life Times of Atmospheric Trace Gases

  26. What is Actually Important in Atmospheric Chemistry? • Ozone - The 'Ozone Problems' • Oxidation Capacity - Removal of 'Pollutants' • Free Radicals - The 'Driving Force' • Greenhouse Gases - Chemistry – RadiationLink • Aerosol - 'Liquid - Solid'

  27. Influence of Trace Gases on the State of the Atmosphere + Gas enhances the effect. - Gas reduces the effect. +/- Depending on conditions the influence can be positive or negative. E.g. NOX (= NO + NO2) can both, enhance or reduce the stratospheric O3 destruction.

  28. The ‘Floors’ of the Atmosphere • It appears appropriate to divide the atmosphere in individual layers – similar to the floors of a building. • Customary divisions follow pertinent physical properties of the atmospheric layers: • ·The thermal Structure or stability of individual layers: Troposphere sphere of the weather Stratosphere 'layered' sphere Mesosphere 'intermediate' sphere Thermosphere 'hot' sphere  • ·The Degree of Ionisation: Neutrosphere low ion density Ionosphere high ion (electron) density • The dominating Mixing Mechanism: Homosphere homogeneous, (turbulent) mixing Heterosphere heterogeneous (diffusive) separation R.G. Fleagle & J.A. Businger (1963), an Introduction to Atmospheric Physics, Academic Press, New York.

  29. Ionosphere Heterosphere Thermosphere Mesosphere 1% of Earth‘s radius: >99.98% of atmosphere Stratosphere Homosphere 1% of Earth‘s Radius Tropopause Troposphere The ‘Floors’ of the Atmosphere The layers of the atmosphere, division according to the categories temperature, mixing mechanism and degree of ionisation.[Brasseur + Solomon 1986].

  30. The Vertical Structure of the Atmosphere The vertical structure of the atmosphere: Temperature, pressure and air density, physical processes [Bergman Schäfer 2001]

  31. Pressure and Temperature Distribution in the Atmosphere The Atmospheric pressure p0 at the earth’s surface is given by: (1) where MA denotes the total mass of the atmosphere, g the acceleration due to gravity of earth, and RE the earth radius.  Units of air pressure: bar 1 bar = 105 Pa = 105 N/m2 millibar 1 mbar = 102 Pa = 1 Hektopascal Torricelli 1 torr = 1 mm Hg = 133.322 Pa Atmosphere 1 atm = 1.01325 bar = 1.01325105 Pa = 760 torr The atmospheric pressure decreases with height, in particular by changing the altitude by dz the force K on an area F will change by the amount: dF = - gAdz where  denotes the air density. The resulting pressure change dp is given by: dp = dF/A = - gdz

  32. The Barometric Height Formula Expressing the air density  by molar-mass(M)/molar-volume(V) and substituting V = RT/p (R = gas constant, T = temperature) for one mole leads to: Substituting  in the expression for dp: After division by p and integration we obtain: And for the pressure p(z) at the altitude z: For an isothermal atmosphere, i.e. T (and g) being independent of z the above expression can be further simplified (Altitude Pressure Relationship): where the quantity zsis called the atmospheric Scale Height.

  33. The Variation of Pressure with Height in the Atmosphere For T = 273 K we obtain zs = 7974 m, i.e. about the known atmospheric scale height of 8 Km. However, in the atmosphere temperatures around 250 K (200 K to 300 K) are more realistic, thus the statement: „The atmospheric scale height is 71 Km“ best describes the real conditions in the atmosphere. Alternatively we may define the „half pressure heigth“: Z1/2 = (ln2)zs  0.693zs  5 km

  34. The Altitude Pressure relationship, An Alternative View: The energy E(z) of an air molecule in the gravity field of earth is given by E(z) = Mgz. Since the energy is statistically distributed it has to follow an Boltzmann- distribution, i.e. the number of molecules n(z) with the energy E(z) is given by: Since n(z)  p(z), in particular p(0) = p0 (and with M = NLm and R = NLk, NL = Lohschmidt or Avogadro number) follows the well known pressure altitude relationship (Equation. 2).

  35. The Atmospheric Scale Height for some Gases

  36. Separation of the Atmospheric Constituents ? Statement: „Heavy molecules“ (molecules with high molecular weight) are enriched close to the surface. In a hypothetical purely diffusive mixed atmosphere each species would, indeed, assume a vertical distribution according to its individual scale height (Equation. 2, pressure altitude relationship). Where the scale height zs would be inversely proportional to its molecular weight. Table 3 gives some examples. In reality the atmosphere is well mixed by turbulence up to the 'Turbopause' at about 100 Km altitude (see Fig. 5), this layer is called the homosphere. The diffusive separation of constituents only occurs above about 100 Km in the "Heterosphere".

  37. Turbulent diffusion constants, K Molecular diffusion constants, D K, D in cm2/s Turbulent Mixing of the Atmosphere Turbulent „Diffusion constant“ K (according to estimates of several authors) and molecular diffusion constants (D(N2-O2) and D(N2-H)) as function of altitude. The D is proportional to the mean free path of the gas and thus inversely proportional to pressure, therefore D increases exponentially with altitude. Below 100 Km altitude (in the Homosphere) turbulent mixing dominates, thus there is a uniform scale height for all atmospheric constituents (based on the mean molecular weight of air).Above ca. 100 Km (the "Turbopause") in the Heterosphere eventually diffusive mixing dominates, therefore the atmospheric constituents separate in the sense that each species attains an individual scale height.

  38. Heterosphere Homosphere Atmospheric Temperature and Mean Molecular Mass Wikimedia Commons

  39. The Atmosphere and Poisson's Equations of State

  40. The (Dry) Adiabatic Laps Rate Scales are so large, that changes of state (e.g. lifting of an airmass) are adiabatic processes in good approximation: With the barometric hight formula: Temperature gradient: Using the scale hight zS = Mg/RT:

  41. z • Displacement of a fluid parcel upwards (from z2 to z3): • ΘP=const. • ΘP< Θ(z3)  Density of the fluid parcel larger than density of the surrounding fluid  restoring force F z3 (z) T(z) F z z2 F  P The Concept of Potential Temperature

  42. Oxygen-Catastrophe: O2 = 1% of atmosphere  drastic shift in biosphere History of the Atmosphere O2 - below 15%: nothing burns - above 25%: burning is “instant” bacteria: CO2 + H2O  HCHO + O2 i.e. O2 was waste product

  43. cold The Sun! ? formation of one large circulation pattern dominated by convection – heat gradient – gravitation? hot cold The energy supply of the atmosphere • What is the source of energy for the atmosphere?

  44. Some dynamical features Barry+Chorley (1998)

  45. Summary • Atmosphere crucial for live • Atmosphere is a complex and non-linear system, interacting with the other geophysical compartments (ocean, land, ice sheet…) • The primary source of energy is solar radiation • Strongest variability (T, p, …) is in the vertical • Large range of spatial and temporal scales • Hydrostatic equation:

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