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Aerosol without cloud
Aerosol in cloud between drops
Aerosol in cloud drops-DEMA
Aerosol in cloud drops-CSA
Cloud LWC
BC in cloud
BC in aerosol
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(a) Cloud LWC (g/kg) and BC (
µ
g/m
3
)
(b) Solar heating rate (K/hr)
Figure 12.26.
(a) Cloud liquid water content (LWC), clear sky black carbon (BC) concentration, and in-cloud BC
concentration as a function of height for the calculations in (b). (b) Modeled solar heating rates for four cases:
(i) aerosol particles containing BC in the clear sky (“aerosol without cloud”) (in this case, the BC profile in (a) is
the same as the cloudy sky BC profile); (ii) the same aerosol distribution as in (i) but, in this case, interstitially
between cloud drops, above the cloud, and below the cloud (“aerosol in cloud between drops”); (iii) the same
total volume of aerosol BC as in the other cases but with the BC treated as inclusions randomly distributed
within cloud drops using the dynamic effective medium approximation (DEMA) of Chylek et al. (1984) (“aerosol
in cloud drops-DEMA”); and (iv) the same as (iii) but with the aerosol BC treated as inclusions within cloud
drops using the core shell approximation (CSA) of Ackerman and Toon (1981) (“aerosol in cloud drops-CSA”)
From Jacobson (2012).
clouds by biomass burning aerosol particles in Brazil
has been observed (e.g., Kaufman and Nakajima, 1993).
The effect on global climate of absorbing aerosol inclu-
sions within clouds has also been calculated to be sig-
nificant (Jacobson, 2006, 2010b).
in more reflective clouds (a greater cross-sectional area
summed over all cloud drops) and hence a higher COD.
However, as AOD continues to increase, the semidirect
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MODIS
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12.4.3.6. Combined Indirect, Semidirect,
and Cloud Absorption Effects
The indirect, semidirect, and cloud absorption effects
are tightly coupled and must be considered together
when examining the effects of aerosol particles on cli-
mate. This is illustrated in Figure 12.27, which shows
the change in
cloud optical depth (COD)
with increas-
ing
aerosol optical depth (AOD)
, obtained separately
from satellite data and a computer model. COD and
AOD are measures of how much cloud and aerosol par-
ticles, respectively, redirect or reduce sunlight due to
scattering plus absorption of light.
Figure 12.27 shows that, at low AOD, an increase
in AOD increases COD. This is because an increase in
AODisgenerally caused by an increase in the num-
ber of CCN, and an increase in the number of CCN
triggers the first and second indirect effects, resulting
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Model
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Aerosol optical depth (--)
Figure 12.27.
Boomerang curves showing the
correlation between aerosol optical depth and cloud
optical depth over a biomass burning region of Brazil
during September, obtained both from MODIS Aqua
satellite data and separately from a three-dimensional
computer model, GATOR-GCMOM. The hash marks
are uncertainty bars. From ten Hoeve et al. (2011).
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