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assumptions the calculated and observed values of the cloud radiation
absorption turns out to be close to each other. Nevertheless, it is safe to
say that there is no exhaustive explanation for the total set of observa-
tions. Thus, the problemhas not been solved yet as the authorsWiscombe
(1995), Lubin et al. (1996), Bott 1997, Ramanathan and Vogelman (1997),
and Collins (1998) point out.
3.5.2
Comparison of the Observational Results of the Shortwave Radiation Absorption
for Different Airborne Experiments
In the above-mentioned studies of radiation absorption by clouds (confirm-
ing or denying the excessive absorption), the satellite data and the data of
the meteorological network have been mainly used. These observations were
accomplished with different instruments during a long period that called for
complicated statistical data processing. As a result, an averaging picture includ-
ing different types of clouds has been obtained. The absence of either uniform
data or a common methodology for data choice and processing is likely to lead
to the contradictory conclusions in the studies hereinbefore described.
Let the airborne observations considered in the previous section be ana-
lyzed in terms of factor
f
s
.Absorption
R
(
F
↓
−
F
↑
)
top
−(
F
↓
−
F
↑
)
base
in the
atmospheric layer with andwithout clouds is computedwith the airbornemea-
surements of SWR. Table 3.2 demonstrates the conditions and results of the
airborne experiments and the values of factor
f
s
for the total (within spectral
region 0.3-3.0
=
µ
µ
m)radiationmeasure-
ments as values of the total absorption in the layer of the clear or cloudy
atmosphere. The results of the airborne observations are seen to allow fixing
of the effect of the strong shortwave anomalous absorption (
f
s
>
1) in a set of
cases. In other cases there is no influence of clouds on the radiation absorption
(
f
s
m) and spectral (for wavelength 0.5
=
1) and in some cases the strong reflection of solar radiation by clouds
even prevents its absorption by the below cloud atmospheric layer and by the
ground surface (
f
s
<
1).
3.5.3
Dependence of Shortwave Radiation Absorption upon Cloud Optical Thickness
In accordance with the results of the experiments either in pure and dust clear
atmosphere or under overcast conditions the relative value of SWR absorption
b
(
µ
0
is presented as a function of the optical thickness in the
studies by Kondratyev et al. (1996, 1997a, 1997b) and Vasilyev A et al. (1994).
The approximation of the experimental points has elucidated the linear de-
pendence of function
b
(
µ
0
,
τ
=
|π
)
R
S
τ
)thatisconfirmingtheanalyticalexpressionforSWR
absorption presented in the topic by Minin (1988). Table 3.2 demonstrates dif-
ferent magnitudes of factor
f
s
. It is close to unity for the thin clouds with optical
thickness
τ
≤
7 especially in the pure atmosphere in the Arctic region. In cases
with a high content of sand and black carbon aerosols it is valid
f
s
≥
2.5 at
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