Solar radiation extinction in the atmosphere

Incoming SR
Diffused part of SR
Absorbed part of SR

(O3), Oxygen (O2), Water vapor (H2O), and Carbon dioxide (CO2).
Ozone

1,87; 2,7; 3,2

1,44; 1,6; 2,02; 2,7; 4,31;

vapor in a column of air with the base 1

bi and βi are quantities empirically obtained.

Mass of the water vapor in the atmosphere is larger than that of ozone and carbon dioxide. Hence, it absorbs the larger part of the total absorbed radiation.

Nitrogen does not absorb radiation. Solid aerosols also absorb SR. In the layer 0,3 – 8,4 km O2 and CO2 absorb 3,8% and solid aerosols absorb 4,8% of SR.

разных направлениях любых веществ, предметов и даже людей)
Dispersion (синоним Scattering,

в науке применяется к свету)
Turbidity (мутность).
The atmosphere is turbid medium due to many admixtures (aerosols) suspended in the air.
Aerosols scatter and absorb solar and terrestrial radiation.

SR even in the absence of aerosols. In this case

turbidity is molecular complexes.







The essence of the scattering is a particular form of interaction between variable field of coming electromagnetic waves and particles in the medium. Due to this kind of interaction the particles become sources of new electromagnetic waves.

Nobelprize.org. 22 Sep 2010 http://nobelprize.org/nobel_prizes/physics/laureates/1904/strutt-bio.html
1842 - 1919

scattering ( the photon energies of the scattered photons is

not changed)
Scattering in which the scattered photons have either a higher or lower photon energy is called Raman scattering.
Usually this kind of scattering involves exciting some vibrational mode of the molecules, giving a lower scattered photon energy, or scattering off an excited vibrational state of a molecule which adds its vibrational energy to the incident photon.

which bears his name in 1928 and for it he

was awarded the Nobel Prize for Physics in 1930.

makes fluxes of the radiation of the same wavelength.
This process

is greatly influenced by the geometrical structure and properties of the turbid medium. The geometrical structure is determined by dimensionless parameters and The laws of scattering are quite different for the

cases and .

If , the particles can be regarded as independent emittants.
The phenomenon of interference will not be observed.
No additional fields of radiation will appear.
Instead, the intensities of the radiation will be summed up. This simplifies solution of the problem of, so called, multiple scattering.

the previously scattered radiation.
Multiple scattering can be neglected if the

medium turbidity is not very high, i. e. the scattering particles are very distant from each other

the properties is complex index of refraction.

is absolute index of

refraction
is characteristics of absorption
The theory of the molecular scattering had been developed by English scientist Rayleigh, who put in the base of the theory the following assumptions:
All particles have form of a ball. They are dielectrically homogeneous and r<<λ.
Particle index of refraction does not markedly differ from that of the medium: nμ<1 and μ=2πr/λ.
The particles diffuse the light independently, I. e. L>>λ
The diffused light is observed at the distance R>>r

theory)
Aerosol particles are much larger than molecule complexes
There are

two types of the larger particles in the atmosphere: non-transparent ones (dust, ), and transparent ones (water droplets).

Water droplets absorb radiation of ultraviolet and visible parts of the spectrum just slightly. Absolute index of refraction for water droplets varies not significantly. It average value n=1,33.
n is absolute index of refraction

function of quantity
m - complex index of refraction,
N

is the number of particles in a unit of volume.
For very large particles (10In case r>40 μ, the scattering does not depend on wavelength.

the atmosphere the sky becomes of whitish color (instead of

light blue) due to the fact that the light dispersed in the same way regardless which wavelength is dispersed.
Due to the same reason, clouds and fogs have white (whitish) or gre`y color.
Scatter indicatrix for several values of parameter μ.

4

30

8

The larger particles mainly scatter in the direction of incident beam

scattered radiation on direction.
http://hyperphysics.phy-astr.gsu.edu/hbase/atmos/blusky.html#c4

some kind of aerosols always exists, both molecular and aerosol

scattering goes on simultaneously.
It makes difficult to estimate real scattering quantitatively from the theoretically obtained equations. Instead some empirical or semi-empirical relations are used for the purpose. It was learnt that regularities of the scattering strongly depends upon the sizes of the particles, and, first of all, on the water droplet sizes.
Very important characteristics is so called scattering index Kλ.

Molecular scattering index

Aerosol scattering index

Prevails up to 3 – 4 km

Prevails above 3 – 4 km

depends on turbidity

depend on turbidity too

up through the whole atmosphere is termed optical depth of

the atmosphere.

is the optical depth caused by molecular scattering, and is that caused by the total scattering.
In the ultraviolet area (λ<40μ) the molecular scattering makes the larger contribution in the total scattering, at λ=0,45 both contribution are almost equal, at λ>0,45 aerosol scattering contribution prevails.

of a 5 mW green laser pointer is visible at

night due to Rayleigh scattering and airborne dust.

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