84974: carynvms'huji'ac'il":

1
????? ???????????? ??????????

• ?"? ??? ?????
• ????? ????? ???? ???? 313
• 8-4974?? caryn_at_vms.huji.ac.il???"?

2
Importance of Radiation in the Atmosphere

• Exchange of energy between the planet and the
  universe
• Exchange of energy between atmosphere and surface
  and between atmospheric layers
• Driving the general circulation
• Photochemical reactions
• creation and destruction of ozone
• photochemical smog
• photosynthesis
• Optical effects
• color of the sky
• appearance of clouds
• rainbows, halos, corona
• visibility

Jacobson, 1999, p. 246
3
The Spectrum of Radiation
Strahler and Strahler, 1992, p. 39

• What creates radiation of different energies?

• What determines the energy of radiation created?

• an accelerating charge (antenna)
• energy transitions by nuclei (gamma decay), atoms
  and molecules (emission)
• fission, fusion (suns proton-proton cycle)

• composition (energy levels)
• available energy
• temperature

4
An Example of Temperature Dependence Black Body

• What is a black body?
• What law from statistical mechanics describes the
  amount of radiation emitted by a black body?
• What happens as T changes?

• absorbs all incident radiation, emission is
  maximum

5
Relevance of Black Body Radiation to Earth

• Emission from sun
• Emission from surface
• Atmosphere
• BUT there is an important difference between the
  emission spectra of the sun and the
  earth/atmosphere

6
Radiative Equilibrium Slab Model of Earth

• At top of atmosphere
• At surface
• To calculate - need to integrate Plancks law
  over ?
• Stefan-Boltzmann law

7
Add the Atmosphere

• In atmosphere
• At surface

BUT too hot for global mean temperature
8
The Atmosphere is Not Really a Black Body
Salby, 1996, p. 217
Jacobson, 1999, p. 264
9
Approximate the Atmosphere as a Grey Body

• In atmosphere
• At surface

Kirkhoffs law
10
Interaction of the Atmosphere with Solar
Radiation - Absorption
Goody and Yung, 1989, p. 190
Jacobson, 1999, p. 262
11
Importance of Atmospheric Absorption of Solar
Radiation
Thomas and Stamnes, 1999, p. 2
12
Interaction of the Atmosphere with Solar
Radiation - Scattering
Wallace and Hobbs, 1977, p. 307
Liou, 2002, p. 89
13
Rayleigh ScatteringSteady E-field Applied to a
Dielectric Sphere

• Maxwells equations (no free charges,
  non-conducting)
• In spherical coordinates (axially symmetric)
• Solutions
• Boundary conditions

Laplaces equation
Legendre polynomials
14

• Solution
• Let E-field oscillate in time
• Conditions

dipole moment
15

• Intensity of Radiation

Poynting vector
16
Mie ScatteringVarying E-field Applied to a
Dielectric Sphere

• Maxwells equations (no free charges,
  non-conducting)
• Vector Helmholtz equation
• With spherical symmetry can be expressed
• In spherical coordinates
• Boundary conditions

17

• Solutions

18
Geometric Optics

• Wave fronts
• Refraction (Snells law), reflection, diffraction
  dispersion

19
Full Time-Independent Radiative Transfer Equation

• In an atmosphere of arbitrary geometry
• In a plane-parallel atmosphere

Plancks function
20
Research Topics

• Climate forcing

IPCC, 2001
21
Research Topics cont.

• Climate change
• What sky coverage by absorbing particles is
  necessary to switch from warming to cooling?
  (radiative convective model simulation Fortran)
• Can a layer of absorbing particles above an ice
  covered planet warm the planet? (radiative
  convective model simulation Fortran)
• Radiative properties of drop mixtures mixing
  rules versus scattering simulations
  (calculations/simulations Matlab, Fortran)
• Satellite detection of rainfall amount and ice
  content (model simulation Fortran)
• Broken clouds
• Is there an efficient yet accurate way to
  describe the flux of radiation above and below
  inhomogeneous cloud fields? (review topic)
• Radiative properties of non-spherical particles
  (review topic)