Spectral Measurements of Solar Irradiance and Radiance in Clear and Cloudy Atmospheres - Short-Wave Solar Radiation in the Earth's Atmosphere - page 120

the study by Li et al. (1995). The results of this study include the latitudinal
dependence of parameter f s citedinFig.3.20aasasolidline.Theresultsofthe
airborne observations (Kondratyev 1972; Kondratyev et al. 1973a; Kondratyev
and Ter-Markaryants 1976; Kondratyev and Binenko 1981; Kondratyev and
Binenko 1984; Vasilyev O et al. 1987; Grishechkin et al. 1989; Vasilyev A et al.
1994) are presented in the same figure. Squares and dashed lines correspond to
the total shortwave observations with the pyranometer, which almost coincide
with the data of the study by Li et al. (1995). Circles and dotted lines correspond
to the observations at a wavelength equal to 0.5 µ m and they show crucially

larger values than the results of the total observations while keeping the same
latitudinal dependence. As hereinbefore described the values of parameter f s
exceeding 2.0 indicate the high content of the absorbing aerosols together with
the large optical thickness of the cloud.
The variations of the anomalous absorption with solar zenith angle were
studied in Imre et al. (1996) and Minnet (1999). The authors Imre et al. (1996)
derived the relationship between parameter f s and solar zenith angle, which we
are citing in Fig. 3.20b (nomograph) together with our results of the airborne
observations (Kondratyev 1972; Kondratyev et al. 1973a; Kondratyev and Ter-
Markaryants 1976; Kondratyev and Binenko 1981, 1984; Vasilyev O et al. 1987;
Grishechkin et al. 1989; Vasilyev A et al. 1994) (squares indicate total spectrum
data, triangles indicate data at wavelength 0.5 µ m). The solar angle dependence

of the airborne data of the total irradiances is evidently coinciding with the
data of Imre et al. (1996) while the dependence in question for wavelength
0.5 µ m is significantly higher. It should be pointed out that the mentioned

coincidence reflects the essence of the specific features of radiation absorption
in cloudy atmosphere, though the results either by Imre et al. (1996) and Li et
al. (1995) or by Kondratyev (1972), Kondratyev et al. (1973a), Kondratyev and
Ter-Markaryants (1976), Kondratyev andBinenko (1981, 1984), VasilyevOet al.
(1987), Grishechkin et al. (1989), andVasilyevAet al. (1994) were obtainedwith
different instruments, methodologies of measurements and processing. Thus,
the excessive (anomalous) absorption really exists and it is mostly evinced in
the shortwave spectral region.
The main result of the study by Minnet (1999) is the following: “solar zenith
angle is critical in determining whether clouds heat or cool the surface. For
largezenithangles( µ 0 > 0.15) the infrared heating of clouds is greater than

the reduction in insolation caused by clouds, and the surface is heated by the
presence of cloud. For smaller zenith angles, cloud cover cools the surface
and for intermediate angles, the surface radiation budget is insensitive to the
presence of or changes in, cloud cover.” The linear dependence of the cloud
radiative forcing upon the cosine of the solar zenith angle in the Arctic has
been revealed in the study by Minnet (1999).
The impact of the thick cloudiness and black carbon aerosols on the solar
radiation absorption has been revealed in the study by Liao and Seinfield
(1998) to produce the forcing values three times higher than those under the
cloud-free conditions. Moreover, it is increasing with the growth of cosine of
the solar zenith angle. Thus, the absorbing aerosols within the clouds cause
the cloud radiation absorption.