General single-scatter properties:  e = Extinction cross-section (m 2 /particle): fraction of incident beam that is attenuated (f) times the cross-sectional area of the incident beam (A)  0 = Single-scatter-albedo: ratio of scattering/(scattering+absorption) P(  ) = Phase function (Sr -1 ): angular distribution of scattered radiation  Scattered radiation: I f  0 P(  ) Transmitted Beam: I(1-f) Incident Beam: I Absorbed radiation: I f  0 ) Isotropic scattering: p(  ) = 1

Regimes of Scattering

Scattering regimes Why does Q  2? Not 1? Rayleigh Regime Q~x 4 Geometrical Optics Regime Q  2

Scattering Efficiency as Function of Size

Carbon Extinction Efficiency

Phase Function     = Scattering angle p(  ) = Scattering phase function Azimuthally symmetric for spheres and randomly oriented particle ensembles Essential for determining the source function for scattering Very strong, narrow forward peak develops for largest particles (diffraction peak). x << 1 x ~ 1 x ~ 10

Why does Q  2? Not 1?

Phase Function for Soil and Sulfate

Phase Function for Carbon

Scattering by a dipole: Rayleigh Scattering + No electric field Electron Shell (-) Nucleus (+) + - Vibration of the electron about the nucleus creates a secondary wave at the same frequency that radiates in all directions, except parallel to the primary electric field. Scattering coefficient ~ -4, so blue scatters much more than red. Induced Dipole

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Mie Solutions for Q E QEQE n r = 1.5 nini nini nini nini

Upon the Blue Ridge Mountains…  = 2?