1. III/1 Atmospheric transport and chemistry lecture I.Introduction II.Fundamental concepts in atmospheric dynamics: Brewer-Dobson circulation and waves III.Radiative transfer, heating and vertical transport IV.Stratospheric ozone chemistry

2. III/2 The role of radiation in the atmosphere radiation transfers energy through the atmosphere  Absorption of UV-VIS-near IR radiation  drives photochemistry  heats the atmosphere  Emission of (thermal) IR radiation cools the atmosphere radiation balance determines atmospheric temperature, and drives atmospheric dynamics

3. III/3 Radiation: chemistry and temperature photoionisation:X + h  X + + e -  ions are highly reactive; photoionisation starts ion-chemistry chains photodissociation:AB + h  A + B  A and/or B can be radicals: photodissociation drives photochemistry photodissociation:AB + h  A + B*  excited-state gas B* can transfer its excitation energy into thermal energy by colliding with other molecules  photodissociation heats the atmosphere absorption:X + h  X*  excited-state gas X* can transfer its excitation energy into thermal energy by collissions  absorption heats the atmosphere thermal emission:X*  X + h  emission from thermally excited states transfers thermal energy into (mainly IR) radiation  emission cools the atmosphere Solar shortwave radiation is turned into terrestrial longwave radiation

4. III/4 Solar and terrestrial radiation Solar irradiance top-of-atmosphere (TOA): Turco 1997

5. III/5 Solar and terrestrial radiation Solar irradiance top-of-atmosphere (TOA): Turco 1997

6. III/6 Solar and terrestrial radiation Solar irradiance top-of-atmosphere (TOA): solar radiation is a black body with T=5800K attenuated by a factor of 265000, 99% of shortwave radiation below 4  m terrestrial radiation is a black body with T=288K 99% of longwave emission above 4  m Turco 1997

7. III/7 Definitions: Spectral radiance Spectral or monochromatic radiance L :  Power transmitted (energy flux density) thru a surface dA into the cone extended by d   Units of L : [L ]=W/m 2 ·nm·ster. spherical coordinates:  zenith angle  azimuth angle

8. III/8 Definitions: Spectral irradiance Spectral irradiance F :  Integration of the spectral radiance over both hemispheres  [F]=W/m 2 ·nm

9. III/9 Irradiance: upward and downward flux plane-parallel atmosphere upward flux downward flux

10. III/10 Total irradiance Net upward irradiance (flux density):

11. III/11 Definition: actinic flux Units: [  ]= W/m 2 ·nm total flux of photons arriving at position r the actinic flux is independent of the direction of the flux! the value significant for photochemistry: actinic flux expressed in units of photons per m 2 nm Actinic flux: integral of the spectral radiance over 4 

12. III/12 Definitions: actinic flux and mean radiance Actinic flux: integral of the spectral radiance over 4   [  ]= W/m 2 ·nm mean radiance:

13. III/13 Net upward irradiance: Diabatic heating rate is proportional to the absorbed radiative power in a slab of thickness  z:  Upward power flux at z (area A):  Upward power flux at z+  z :  Difference between both terms is the absorbed radiative power that results in heating Irradiance and diabatic heating Diabatic heating rate in K/day

14. III/14 Diabatic heating and vertical transport Diabatic heating rate in K/day typical values of q: 1 K / day

15. III/15 Diabatic heating and vertical transport Diabatic heating rate in K/day typical values of q: 1 K / day Potential temperature

16. III/16 Radiative transfer Transmission of light through atmospheric layer N Light is  absorbed by trace gases (UV/IR)  scattered out of the beam (UV/VIS) by  air molecules (Rayleigh scattering)  particles/aerosols (Mie scattering)  emitted by trace gases (IR)

17. III/17 Radiative transfer Transmission of light through atmospheric layer N Consider a single absorber in atmospheric layer N:  ,a : absorption cross-section of absorber a at wavelength  n a : number density of absorber a  L : spectral radiance at wavelength Integration along a path from point s o to s yields Beer-Lambert law:

18. III/18 Radiative transfer equation general radiative transfer equation (Rayleigh scattering + a number of absorbers and emitters):  ,j : emission probability of j-th emitter at wavelength  B : emission source term

19. III/19 Radiative transfer equation differential formulation of the radiative transfer equation: Integral from of RT equation: emission term absorption term

20. III/20 Radiative transfer equation Optical thickness  : Integral from of RT equation: emission term absorption term

21. III/21 Solar radiation and chemistry Optical depth Penetration altitude= unit optical depth

22. III/22 Solar radiation and chemistry Optical depth Penetration altitude= unit optical depth Chappuis band Huggins band Hartley band

23. III/23 Solar radiation and chemistry (2) Chappuis band Huggins band Hartley band

24. III/24 UVB radiation at surface (erythema weighted) UV index  integrated UV-B (290-320 nm) radiation at the surface  screened by clouds  modified by O3 absorption  solar zenith angle dependent  surface radiation F( ) is weighted by erythema sensitivity A( ) (action spectrum for sun burn)  Calculated normally for noon condition A( )F( ) F( ) ·A( ) Madronich and Flocke, 1997

25. III/25 Atmospheric window(s) Absorption A: Transmission T: greenhouse gases in IR atmospheric window

26. III/26 Solar heating from O2 and O3 Maximum solar heating in summer extratropical stratopause (~1 hPa) Mlynczak et al. 1999

27. III/27 Solar heating: contribution of absorbers Mertens et al. 1999 in the stratosphere, solar heating is dominated by O 3 Chappuis Hartley Huggins

28. III/28 IR emission cooling  cooling is dominated by CO 2  maximum cooling rates in the summer extratropical stratopause (~ 1 hPa)  there is nearly a balance between cooling (CO2) and heating (O3) summer winter

29. III/29 Solar heating and IR emission cooling London 1980

30. III/30 Radiative lifetime and radiative equilibrium Net zonal mean heating rate q from solar heating (SH) and IR cooling/diabatic relaxation (proportional to zonal mean temperature):  : Newtonian cooling coefficient (1/  : radiative life time) Mlynczak et al. 1999 Pinatubo strat. aerosol (UARS)  depends on the distribution of emitters (CO 2, O 3, H 2 O), here is also a contribution from stratospheric aerosols

31. III/31 Radiative lifetime and radiative equilibrium Net zonal mean heating rate q from No wave forcing, then q=0 and radiative equilibrium temperature can be estimated as Without wave forcing polar vortex would be extremely cold associated with high polar ozone loss Radiative equilibrium temperature Fels 1985 winter

32. III/32 Radiative lifetime and radiative equilibrium radiative equilibrium temperature Fels 1985 Atmospheric temperature in K from 2 D model (January) Winter polar vortex much warmer than radiative equilibrium !

33. III/33 Global energy budget dynamical heating: wave dissipation (heat) from gravity wave breaking, vertical transport of heat, some convective adjustments, and other dissipative terms heat conduction: molecular thermal conductivity (mainly from thermosphere) chemical heating: released by exothermic reactions from photolysis products, e.g. O+O+M  O 2 +M diabatic heating above 60 km:  solar absorption from O 2 (Schumann- Runge), O 3 (Hartley band), and N 2  IR cooling from CO 2 (15  m band) Fomichev et al. 2002 Results from the Canadian Middle Atmosphere Model

34. III/34 Earth radiation budget Turco 1997