Analysis of Radiative Observations in Cloudy Atmosphere - Short-Wave Solar Radiation in the Earth's Atmosphere - page 253

particles are situated within the droplets (the internal mixture )theaerosol
absorption is correctly accounted for in calculation with the formulas for
one-component medium. Basing on the obtained results one could conclude
that the anomalous absorption by clouds points to the external mixture of
the atmospheric aerosols and cloud droplets because in the opposite case the
radiation absorption by clouds coincides with the theoretical values.

7.5.2
Multiple Scattering of Radiation as a Reason for Anomalous Absorption
of Radiation by Clouds in the Shortwave Spectral Region

The aerosols consisting of hydrophobic particles such as sand, soot etc. could
exist within the cloud between droplets with higher probability than the hy-
drophilic ones (salt, sulfates); hence, they increase the shortwave absorption
of radiation by the cloud. Hydrophilic particles, being the nuclei of conden-
sation increase the droplet number. This obstacle in turn increases the cloud
optical thickness and causes the cloud cooling. The aerosol absorption by the
cloud increasing up to 15% has been approximately estimated basing on the
proposed mechanism with the mean values of the aerosol volume absorption
coefficient equal to 0.08 km −1 and of the volume scattering coefficient equal to
30 km −1 with geometrical thickness ∆ = z 1 km and within spectral range 0.4-

µ 1.0 m. Themolecule absorptionwithin the ozone Chappuis band increases up

to 6-10% and the molecule absorption within oxygen band 0.76 µ m increases

up to 10% that coincides with the results of the study by Dianov-Klokov et al.
(1973). This effect turns out stronger for the thicker clouds, and it quantitatively
explains the anomalous absorption by clouds.
Experimental studies (Boers et al. 1996; Bott et al. 1996) actually indicate the
higher content of the carbonaceous andmineral compound in the atmospheric
aerosols than has been assumed before together with their significant yield to
forming the radiative regime of the atmosphere. The hydrophobic particles
could be injected into the atmosphere as the result of industrial escapes, sand
storms, volcanic eruptions, and fires. These sources do not seem enough to ac-
count for the cloud anomalous absorption displayed on a global scale, however
the aerosols flue escapes extend up to 3000 km keeping their radiation activity
in the optical range (Mazin and Khrgian 1989).
In the remainder of this chapter, we would like to point out that careful
accounting of the optical properties of all atmospheric components is necessary
for the construction of optical models (Vasilyev and Ivlev 2002).

References

Asano S (1994) Cloud and Radiation Studies in Japan. Cloud Radiation Interactions and
Their Parameterization in Climate Models. In: WCRP-86 (WMO/TD No. 648), WMO,
Geneva, pp 72-73
Binenko VI, Kondratyev KYa (1975) Vertical profiles of typical cloud forms. In: Main Geo-
physical Observatory Studies 331, pp 3-16 (in Russian)