A Plan for a Research Program on Aerosol Radiative Forcing and Climate Change (1996) / Chapter Skim
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APPENDIX A ILLUSTRATIONS OF RECOMMENDED RESEARCH, EMPHASIZING RECENT LITERATURE
APPENDIX A ILLUSTRATIONS OF RECOMMENDED RESEARCH, EMPHASIZING RECENT LITERATURE
Pages 135-158
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From page 135... ...
All studies should give information on mass fluxes as well as size distribution in the range between 0.01 and 10 lam radius. We recommend that the transformations of atmospheric trace gases which lead to particle formation be studied.
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From page 136... ...
We recommend comprehensive comparative studies of the radiation fields for clean and polluted atmospheres in order better to identify the effects of short- and long-wave radiation on the atmosphere and its modification with increasing pollution. We recommend measurements of albedo and other radiative properties of clouds and fogs in unpolluted and polluted areas, in conjunction with sufficiently complete measurements of cloud microstructure.
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From page 137... ...
We recommend that the optical properties of cirrus clouds, in both solar and infrared radiation, be investigated. We recommend that high priority be given to monitoring trends, if any, in cirrus cloudiness and characteristics.
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(19883. Have the concentrations of tropospheric aerosol particles changed?
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Wiley, New York: The strong dependence of the local planetary albedo change on aerosol particle size distribution change and soot content underlines the need for more reliable input parameters and more sophisticated models before the sign and the relative magnitude of an aerosol climate signal .
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Satisfactory quantitative analysis of the net climate forcing owing to anthropogenic aerosols will be difficult, because of the inhomogeneous distribution of the aerosols. It will be necessary to monitor global tropospheric aerosol properties, and carry out in situ case studies under a broad variety of conditions.
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Levy II (1992~. Sources of nitrate and ozone in the marine boundary layer of the tropical North Atlantic.
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Warren (19911. Perturbation of the Northern Hemisphere radiative balance by backscattering from anthropogenic sulfate aerosols.
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The relative roles of sulfate aerosols and greenhouse gases in climate forcing. Science 260, 311-314: To define better the direct forcing due to sulfate aerosols, more comprehensive and simultaneous observational data are needed on the chemical, physical, and radiative properties of the aerosol.
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From page 144... ...
Satellite measurements capable of giving not just cloud cover (and cloud-top temperature) but also some information about cloud microphysics would be valuable, especially if the measurements continued unaltered over long periods of time.
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Although our understanding of the effect of intense pollution on cloud microphysics is by no means satisfactory, efforts should be focused on obtaining more data concerning the effect of anthropogenic sulfate, and other aerosol species, at concentrations more typical of global sulfate concentrations [i.e., <50 nEq m~3;. There is a clear need to study the relationships among Nd, CCN, and sulfate in detail before parameterizations of this nature can be properly
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. ., this was thought to require the large supersaturations present in cumuliform clouds, rather than the smaller values characteristic of marine stratiform clouds, which are most important for radiative forcing.
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From page 147... ...
As shown here, the simultaneous measurement of mass and number size distributions is useful in studying how the DMS oxidation products are distributed between particle production and growth. However, existing methods for measuring mass size distributions need to be modified or new techniques developed such that these size distributions can be measured on a shorter time scale and .
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, more detailed studies on the kinetics of DMS oxidation under conditions typical of the MBL [marine boundary layer] are needed.
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Third, with increased HNO3 concentrations the disappearance of the cloud droplets due to evaporation is slower. In marine regions the nitric acid concentrations are usually several orders of magnitude lower than those needed to significantly change the numbers of CCN, [but]
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The increases in cloud cover could be indirectly related to the observed global warming and increases of greenhouse gases, related to the indirect effects of increases in aerosols, simply a manifestation of natural climate variability, or a combination of all three. A robust answer regarding the causers)
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Res., in press: Tropospheric aerosols alone cannot provide the continentally located forcing, i.e., they are not capable of damping the diurnal cycle as much as observed. Only an increase of continental cloud cover, possibly a consequence of anthropogenic aerosols, can damp the diurnal cycle by an amount comparable to observations.
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. argued that increased CCN concentrations, which decrease cloud droplet sizes and reduce drizzle, can increase the fractional coverage of marine stratiform clouds because drizzle can regulate the liquid-water content during the lifetime of a cloud ....
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Science 256, 13 1 1-13 13: Cloud albedo depends on column-integrated liquid water content and the density of CCN .... A comparison of two independent satellite data sets suggests that, although anthropogenic sulfate emissions may enhance cloud albedo immediately adjacent to the east coast of the U.S., over the central North Atlantic Ocean the variability in albedo can be largely accounted for by natural marine and atmospheric processes that probably have remained relatively constant since the beginning of the industrial revolution.
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Cess (1993~. Effect of anthropogenic sulfate aerosols on low-level cloud albedo over oceans.
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From page 155... ...
the relations between mass and number concentrations and composition of precloud aerosol concentrations and the number, concentration, and size distribution of cloud droplets formed in air containing the aerosol; and (ii) the dependence of aerosol perturbation to cloud radiative forcing on the nature of the cloud fields.
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From page 156... ...
Among the components of such a research program would be a new set of satellites dedicated to questions of radiative forcing and able to provide the needed global coverage and high frequency of sampling. Connection of this global data set to local and column integral optical, chemical, and microphysical properties requires a set of ground-based observing sites carefully located to delineate the key characteristics of air masses that are either influenced or unaffected by anthropogenic sulfate.
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From page 157... ...
Dahlem Konferenzen 1994, Wiley, New York: The detection of an anthropogenic sulfate aerosol forcing on the surface air temperature is supported by a new analysis of daily surface air temperatures, cloud amount, and SOX emissions in North America. Within the contiguous U.S.A., SOX emissions increased by about 8 Tg between 1950
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From page 158... ...
The direct radiative forcing due to increases in sulphate aerosol since 1850, averaged globally, is estimated to lie in the range -0.25 to -0.9 W m~2. The direct effect of aerosol from biomass burning is estimated to lie in the range -0.5 to -0.6 W m~2.
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