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estimate of RF, but revealed a shift of maximum indirect effect of aerosol to the
tropical zone. Experiments on sensitivity have led to the conclusion that the impact
of changes of cloud droplets radius is about 3 times stronger than that of changes of
clouds lifetime, as well as that the contribution of carbon aerosol is small compared
to total indirect climatic impact of aerosol. An approximate character of the
obtained results is determined,
for
instance, organic carbon aerosol (this is connected with the absence of needed
information about aerosol), as well as an exclusion from consideration of ice clouds
and the impact of the processes discussed on the LWR transfer. The climate model
is planned to be further developed by taking into account the ocean-atmosphere
interaction with stronger emphasis on regional effects.
Cook and Highwood (2004) have been the
first of all, by neglecting some types of aerosol
—
first who undertook a numerical
modeling of the climatic impact of aerosol absorbing solar radiation within the
“
model of atmospheric general circulation, IGCM, developed at Reading
University (USA). The 22-layer global model IGCM of the system
interim
”
“
atmosphere
—
2-m mixed layer of the ocean
long. and
ensures a simulation of equilibrium climate after integration for a period of 5 years
(in fact, calculations have been made for 30 years). The results obtained in Cook
and Highwood (2004) indicate that the sign of direct ARF cannot be considered as a
representative characteristic of the sign of real changes of global average annual
average SAT. The related important fact is that the climatic sensitivity to radiation
absorbing aerosol is much stronger than the climatic sensitivity to the
”
has been realized over the grid 5
°
lat.
×
5
°
”
warming due to the growth of CO
2
concentration. The situation is determined by a
change of cloud amount in the process of climate formation (SAT change).
When single-scattering albedo of the aerosol is <0.95, the low-level cloud amount
decreases, which determines the functioning of the respective positive feedback. On
the other hand, changes of the upper-level cloud amount manifest themselves as the
process of negative feedback formation. The total impact of clouds is determined by
the balance between two effects of the opposite signs and depends strongly on the
choice of the parameterization scheme for the cloud cover dynamics. These results of
numerical modeling revealed a distinct
“
greenhouse
impact of aerosol on climate. In
this connection, a supposition has been made in Cook and Highwood (2004) that in
all GCM models, the aerosol-cloud feedback due to absorbing aerosols is implicitly
present. This situation suggests the conclusion about critical importance of an
adequate parameterization of cloud cover dynamics (in particular, in the context of
hypothesis of
“
semi-direct
”
ARF proposed by Hansen et al. (1997)). According to
IGCM model, clouds play an extremely important role in the formation of the
climatic system
“
semi-direct
”
s response to the atmospheric aerosol dynamics.
Takemura et al. (2005) applied a coupled model of the long-range transport and
atmospheric general circulation to estimate changes of cloud cover characteristics,
precipitation, and temperature due to direct and indirect ARF. The obtained esti-
mates of the ef
'
cient radius of cloud droplets, cloud-induced RF (CRF) are in
satisfactory agreement with the data of satellite observations. The numerical
modeling revealed a global-scale decrease of an ef
cient radius of droplets due to
indirect anthropogenic ARF. On the other hand, changes of the cloud water and
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