Atmospheric Composition and Temperature Variations - Understanding the Basics

1. Today’s Agenda • Quick In-class Practice Quiz • Review up to material in the last lecture

2. Temperature Questions • What causes annual and diurnal temperature variations? • Do hottest/coldest temperatures occur during maximum/minimum input of solar radiation? • What physical processes modulate temperature variations?

3. The Blue Marble ATMO 170Lecture Atmospheric Composition Mass, Density, Pressure Vertical Structure Photo from Apollo 17

4. What is air made of? N2 and O2 are most abundant Concentrations (except O3) are constant up to ~80 km N2 and O2 are chemically active, continuously cycled Ar, Ne, He, and Xe are chemically inert trace gases H2O, CO2, CH4, N2Oand O3 important greenhouse gases variable

5. AerosolsNatural and Anthropogenic Sources

6. Fundamental Concepts Three properties that characterize the air Mass – amount of matter; inertia Density – mass/volume Pressure – force per area

7. How Pressure Changes with Height 1 mb log 100 = 0 log 101 = 1 log 102= 2 log 103= 3 48 km 48 km - 1 mb 32 km - 10 mb 16 km - 100 mb 0 km - 1000 mb ±16 km 10x change 10 mb 32 km ±16 km 10x change 100 mb 16 km ±16 km 10x change This relationship can be easily quantified by noting for For every 16 km in altitude ☞ pressure decreases by a factor of ten.

8. Barometer and Altimeter Android App iPhone App

9. inversion isothermal 6.5oC/km Vertical Temperature ChangeDefines layers of the atmosphere Environmental Lapse Rate Rate at which observed temperature decreases with height Inversion Temperature decreases with height Isothermal Temperature constant with height Ahrens

10. ATMO 170LectureWeather and Climate Surface analysis for 20120823 21Z

11. Weather – The state of the atmosphere: at a specific location for a moment in time Weather Elements 1) Temperature 2) Pressure 3) Humidity 4) Wind 5) Visibility 6) Clouds 7) Significant Weather What is Weather? Automated Surface Observing System Tucson International Airport

12. Surface Station Model Responsible for underlined parameters Temperatures Plotted °F in U.S. Sea Level Pressure Leading 10 or 9 is notplotted Only the 3 rightmost digits are plotted w/o decimal point Example above: 1010.7 mb plotted as 107 common wx rain snow fog thunderstorms Decoding Station Modelhttp://www.hpc.ncep.noaa.gov/html/stationplot_printer.html Practice from CIMMShttp://itg1.meteor.wisc.edu/wxwise/station_model/sago.html

13. Weather vs. Climate • Weather - atmospheric conditions at specific time and place Think Snapshot • Climate - average weather and the range of extremes compiled over many years Think Statistics

14. ATMO 170LectureTemperature vs. Heat Heat Transfer A boiling pot of water illustrates all modes of heat transfer

15. Energy and Heat Transfer • Energy can only converted from one form to another or transferred from one place to another Total energy is conserved

16. Energy and Heat Transfer • Temperature – a measure of the average speed of molecules • Internal Energy –energy an object has due to the movement of its atoms and molecules • Heat (Transfer) –energy transfer due to temperature differences Heat flows from warmer => colder Equilibrates temperature differences

17. Modes of Heat Transfer Three primary modes of heat transfer Conduction – molecule to molecule Convection – vertical transport of fluid Advection => horizontal transport + Latent Heat – energy of phase changes Large for H2O Vapor <=> Liquid Works with fluid motions Radiation – electromagnetic waves

18. ATMO 170LectureLaws of Radiation Depiction of Van Allen belt that protects earth from harmful radiation from the sun

19. Radiation • All mass that has a temperature greater than 0 K, emits radiation. • This radiation is in the form of electromagnetic waves, produced by the acceleration of electric charges. • These waves do not need matter in order to propagate; they move at the “speed of light” (3x108 m/sec; 186,000 miles/sec) in a vacuum

20. Electromagnetic Waves • Important aspects of waves are: • Wavelength: Distance between peaks. • Amplitude: Height of crests • Frequency: # waves that pass a point in one second Period: Time it takes one wave to pass a point Wavelength Distance btw peaks Frequency # crests per unit time Amplitude Height of crests/troughs

21. Electromagnetic Spectrum meteorological significance WAVELENGTH FREQUENCY

22. Plank’s Law: Emission Spectrum Wien’s and Stefan-Boltzmann Laws Energy from an object is spread unevenly over all wavelengths. Emission spectrum of Sun Planck’s Law Energy Emitted Wavelength Ahrens

23. Planck’s Laws Ahrens 7th ed. Wien’s => Hotter the object, shorter the wavelength of max emission. Stefan-Boltzmann => Hotter the object, the more radiation emitted.

24. Take Home Points • All objects above 0K emit radiation • Hotter the object, shorter the wavelength of maximum emission: Wien’s Law Know it • Hotter objects radiate more energy than colder objects: Stefan-Boltzmann LawKnow it • Objects that are good absorbers of radiation are also good emitters.

25. Radiative Equilibrium • Radiation absorbed / emitted by an object increases / decreases the energy of the object. • Increase / Decrease in energy absorbed causes temperaturewarm / cool • When the energy absorbed equals energy emitted, this is called Radiative Equilibrium. • Corresponding temperature is constant Radiative Equilibrium Temperature.

26. ATMO 170LectureSelective AbsorptionGreenhouse EffectGlobal Energy Balance View as Slide Show An artist’s rendition of the greenhouse effect. What’s wrong with this picture? Picture link

27. Properties of Radiation • Radiation has four possible fates • Absorbed • Transmitted • Reflected • Scattered • All four are important in the atmosphere

28. A “Grey Body” = Not all wavelengths absorbedSome are.Some are not.This is How the Atmosphere Behaves SOME REFELECTION SCATTERING OF SUNLIGHT FROM BOX SOME TRANSMISSION OF SUNLIGHT THROUGH BOX GREY BOX SUNLIGHT (SHORTWAVE) INFRARED (LONGWAVE) EMISSION SOME ABSORPTION OF SUNLIGHT BY BOX

29. To explain selective absorption, we turn to Quantum Mechanics

30. Energy States for Atoms Hydrogen Atom Gedzelman1980, p 104 • Electrons can orbit only in permitted states • Each state corresponds to a specific energy level • Only quantum transitions occur between states • Each quantum interval corresponds to a specific wavelength of electromagnetic radiation as electrons accelerate between levels 0.66 0.12 eV=1.25/λ microns

31. H2O vibrational modes Energy States of Molecules Stretching Scissoring Stretching • Molecules also rotate and vibrate • But at specific frequencies or energy levels only • Quantum intervals between energy levels correspond to specific wavelengths of electromagnetic radiation as electrons accelerate between levels CO2 vibrational mode

32. Atmospheric Spectrum UV (<0.3 μm) absorbed by O2 and O3 IR UV VIS Visible(0.4-0.7 μm) NOT absorbed Infrared(5-20 μm) selectively absorbed mostly by H2O and CO2

33. Greenhouse Effect 0°F 59°F The presence of the gases in our atmosphere that absorb and emit infrared radiation helps maintain the Earth’s average temperature at about 59°F. Greenhouse Explanation

34. Atmospheric Energy BalanceComplex Balance Incoming 100 Solar 70 in = 70 out 30 reflected mostly by clouds Atmosphere 160 in = 160 out Infrared 95% absorbed by air Ground 147 in = 147 out Ahrens

35. Primary reason for seasons Tilt of the Earth’s axis. Affects two things • How “high in the sky” the sun is • Length of daylight Earth-Sun Relationship (animation)

36. Chicago - hottest time of year occurs one month after summer solstice Consider Average MAX Temperature for Chicago IL warming warming equilibruim cooling USA Today WWW Site

37. Warmest and coldest days of year occur at points of radiative equilibrium comet.ucar.edu

38. Warmest-Coldest Days Temperature Difference Lutgens and Tarbuck Continents undergo larger changes than oceans High latitudes undergo larger changes than low latitudes

39. Daily Range of Temperatures Ahrens 6th ed. MAX-MIN difference decreases with height Cycle is “felt” up to ~1 km

40. Why do daily MAX-MIN occur when they do? When incoming Solar exceeds outgoing IR Temperature rises When outgoing IR exceeds incoming Solar Temperature falls When outgoing IR equals incoming Solar Radiative equilibrium Temperature peaks MAX occurs Late afternoon MIN occurs After sunrise Ahrens

41. Controls of Temperature • Elevation • Latitude • Land vs. Ocean • Prevailing Wind

42. Take Home Points • Balance between incoming and outgoing energy controls temperature changes. We typically observe… Warmest Day in July; Coldest Day in January MAX is late afternoon; MIN is just after sunrise • Diurnal temp. changes are largest at ground. Affected by wind, cloud cover, land type • Winter-Summer differences Largest over interior of continents and high latitudes • Temperature controls Elevation; Latitude; Land-Sea; Prevailing Wind