lmd_Boucher1995.bib

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@article{1995JGR...10026117B,
  author = {{Boucher}, O. and {Anderson}, T.~L.},
  title = {{General circulation model assessment of the sensitivity of direct climate forcing by anthropogenic sulfate aerosols to aerosol size and chemistry}},
  journal = {\jgr},
  keywords = {Atmospheric Composition and Structure: Aerosols and particles, Atmospheric Composition and Structure: Transmission and scattering of radiation, Meteorology and Atmospheric Dynamics: Radiative processes},
  year = 1995,
  month = dec,
  volume = 100,
  pages = {26117},
  abstract = {{Climate response to atmospheric changes brought about by human activity
may depend strongly on the geographical and temporal pattern of
radiative forcing [Taylor and Penner, 1994]. In the case of aerosols
stemming from anthropogenic sulfur emissions, geographical and temporal
variations are certainly caused by variations in local mass
concentration [Charlson et el., 1991; Kiehl and Briegleb, 1993], but
could also arise from variations in the optical properties of sulfate
aerosols. Since optical properties (including their relative humidity
(RH) variation) depend fundamentally on aerosol size and chemical form
and since size and chemical form are features of the aerosol which are
not likely to be modeled on the global scale in the near future,
geographical and temporal variations in optical properties could
represent a stumbling block to accurate climate change forecasts. While
extensive measurements of aerosol optical properties are needed to fully
assess this problem, a preliminary assessment can be gained by
considering the sensitivity of climate forcing to realistic variations
in sulfate aerosol size and chemical form. Within a plausible set of
assumptions (sulfate aerosol resides in the accumulation mode size range
and only interacts with water vapor and ammonia vapor), we show that
this sensitivity is fairly small ({\plusmn}20\%). This low sensitivity
derives from a number of compensating factors linking the three optical
parameters identified by Charlson et al. [1991]. By implication, these
optical parameters, low RH scattering efficiency, the ratio of
hemispheric backscatter to total scatter, and the RH dependence of
scattering efficiency, should not be treated independently in either
theoretical or experimental investigations of direct climate forcing. A
suggested logical focus for such investigations is the backscatter
efficiency at high RH. If borne out by future research, low sensitivity
to sulfate aerosol size and chemistry would mean that direct sulfate
climate forcing can be incorporated in global climate models with only a
knowledge of sulfate mass concentration. We emphasize, therefore, the
need to study the extent to which our assumptions break down, in
particular, the fraction of anthropogenic sulfate that forms on coarse
mode particles (i.e., those with diameters {\gt}1 {$\mu$}m) and the extent
and effects of sulfate interactions with other accumulation mode
components. Finally, we find that a significant fraction of direct
aerosol forcing occurs in cloud-covered regions, according to a simple
bulk parameterization.
}},
  doi = {10.1029/95JD02531},
  adsurl = {http://adsabs.harvard.edu/abs/1995JGR...10026117B},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}

@article{1995JGR...10016395B,
  author = {{Boucher}, O. and {Le Treut}, H. and {Baker}, M.~B.},
  title = {{Precipitation and radiation modeling in a general circulation model: Introduction of cloud microphysical processes}},
  journal = {\jgr},
  keywords = {Atmospheric Composition and Structure: General or miscellaneous},
  year = 1995,
  month = aug,
  volume = 100,
  pages = {16395},
  abstract = {{Cloud microphysical processes are introduced in the precipitation
parameterization of a general circulation model (GCM). Three
microphysical processes are included in this representation of warm
cloud precipitation: autoconversion of droplets, collection of droplets
by falling raindrops, and evaporation of raindrops falling in clear sky.
The mean droplet radius, r, is calculated from the cloud water mixing
ratio, which is computed in the model, and the cloud droplet number
concentration, N, which is prescribed. The autoconversion rate is set to
zero for r {\lt} r$_{0}$, a prescribed threshold mean droplet
radius. We investigate the model sensitivity to r$_{0}$ and to N,
the cloud droplet concentration, which is linked to the concentration of
cloud condensation nuclei and is likely to vary. We find that an
increase in N leads to an increase in the amount of cloud water stored
in the atmosphere. In further experiments the mean droplet radius used
in the parameterization of cloud optical properties is calculated in the
same way as in the precipitation parameterization in order to bring more
consistency between the different schemes. We again investigate the
model sensitivity to r$_{0}$ and to N and we find that an increase
in N significantly enhances cloud albedo.
}},
  doi = {10.1029/95JD01382},
  adsurl = {http://adsabs.harvard.edu/abs/1995JGR...10016395B},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}

@article{1995TellB..47..281B,
  author = {{Boucher}, O. and {Lohmann}, U.},
  title = {{The sulfate-CCN-cloud albedo effect.}},
  journal = {Tellus Series B Chemical and Physical Meteorology B},
  year = 1995,
  month = jul,
  volume = 47,
  pages = {281},
  abstract = {{Aerosol particles, such as sulfate aerosols, can act as cloud
condensation nuclei (CCN). The CCN spectrum and the water vapour supply
in a cloud determine the cloud droplet number concentration (CDNC) and
hence the shortwave optical properties of low-level liquid clouds. The
capability of anthropogenic aerosols to increase cloud reflectivity and
thereby cool the Earth's surface is referred to as the indirect effect
of anthropogenic aerosols. To obtain an estimate of this effect on
climate, we empirically relate the CDNC, and thus the cloud optical
properties, of two general circulation models (GCM) to the sulfate
aerosol mass concentration derived from a chemical transport model.
Based on a series of model experiments, the normalized globally averaged
indirect forcing is about - 1W/m$^{2}$ and ranges from   0.5 to -
1.5W/m$^{2}$ in both GCMs for different experiments. However, it
is argued that the total uncertainty of the forcing is certainly larger
than this range. The overall agreement between the two climate models is
good, although the geographical distributions of the forcing are
somewhat different. The highest forcings occur in and off the coasts of
the polluted regions of the Northern Hemisphere. The regional
distribution of the forcing and the land/sea contrast are very sensitive
to the choice of the CDNC-sulfate mass relationship. The general
patterns of the forcing, and the appropriateness of the different
CDNC-sulfate mass relationships, are assessed. We also examine the
simulated droplet effective radii and compare them with satellite
retrievals.
}},
  doi = {10.1034/j.1600-0889.47.issue3.1.x},
  adsurl = {http://adsabs.harvard.edu/abs/1995TellB..47..281B},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}

@article{1995JCli....8.1403B,
  author = {{Boucher}, O.},
  title = {{GCM Estimate of the Indirect Aerosol Forcing Using Satellite-Retrieved Cloud Droplet Effective Radii.}},
  journal = {Journal of Climate},
  year = 1995,
  month = may,
  volume = 8,
  pages = {1403-1409},
  abstract = {{In a recent paper, Han et al. analyzed satellite data radiances to
retrieve cloud droplet effective radii and reported significant
interhemispheric differences for both maritime and continental clouds.
The mean cloud droplet radius in the Northern Hemisphere is smaller than
in the Southern Hemisphere by about 0.7 [mgr]m. This hemispheric
contrast suggests the presence of an aerosol effect on cloud droplet
size and is consistent with higher cloud condensation nuclei number
concentration in the Northern Hemisphere due to anthropogenic production
of aerosol precursors. In the present study, we constrain a climate
model with the satellite retrievals of Han et al. and discuss the
climate forcing that can be inferred from the observed distribution of
cloud droplet radius. Based on two sets of experiments, this sensitivity
study suggests that the indirect radiative forcing by anthropogenic
aerosols could he about 0.6 or 1 W m$^{2}$ averaged in the
0{\deg}-50{\deg}N latitude band. The uncertainty of these estimates is
difficult to a assess but is at least 50\%.
}},
  doi = {10.1175/1520-0442(1995)008<1403:GEOTIA>2.0.CO;2},
  adsurl = {http://adsabs.harvard.edu/abs/1995JCli....8.1403B},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}