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Global Climate Change Digest
A Guide to Information on Greenhouse Gases and Ozone Depletion
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FROM VOLUME 9, NUMBER 5, MAY 1996

PROFESSIONAL PUBLICATIONS...
CLOUDS, AEROSOLS & CLIMATE

Item #d96may17

Two items from Atmos. Environ., 30(10/11), May 1996:

"Physico-Chemical Measurements to Investigate Regional Cloud-Climate Feedback Mechanisms," V.K. Saxena (Dept. Marine, Earth & Atmos. Sci., N.C. State Univ., Raleigh NC 27695), P.A. Durkee et al., 1573-1579. Presents mountain top measurements which indicate that the sulfate content of air masses is capable of influencing cloud-climate feedback mechanisms by changing the albedo of thin, continental clouds.

"A 3D Model Study of the Global Sulphur Cycle: Contributions of Anthropogenic and Biogenic Sources," M. Pham (Service d'Aéronomie, 4 Pl. Jussieu, 75 252 Paris Cedex 05, France), J.F. Müller et al., 1815-1822. Compares simulations of the preindustrial and present-day atmospheres produced by the IMAGES 3-D tropospheric chemistry-transport model. They show a large postindustrial increase in the concentrations of SO2 and non-sea-salt sulfates, amounting to a factor of 2 or 3 on a global average, and reaching two orders of magnitude at the surface in some parts of the Northern Hemisphere. Biogenic species such as DMS are also shown to be influenced by industrialization through changes in the oxidizing capacity of the atmosphere.

Item #d96may18

"Unrealistic Desiccation of Marine Stratocumulus Clouds by Enhanced Solar Absorption," A.S. Ackerman (NASA-Ames, Moffett Field CA 94035), O.B. Toon, Nature, 380(6574), 512-515, Apr. 11, 1996.

Recent measurements indicate that clouds absorb up to three times more solar energy than conventional theory predicts, a difference that would have major implications for climate modeling. However, model simulations described here show that either enhanced solar absorption occurs only in clouds other than marine stratocumulus, or the enhancement indicated by the recent measurements is overestimated.

Item #d96may19

Three related items in Nature, 380(6573), Apr. 4, 1996:

"Raising Dust in the Greenhouse," M.O. Andreae (Dept. Biogeochem., M. Planck Inst. Chem., POB 3060, D-55020 Mainz, Ger.), 389-390. Discusses the following two papers, which demonstrate that the amount of dust in the atmosphere is increasing, largely because of human activity. Its climatic importance is becoming clear, and heightens rather than reduces our concern about anthropogenic climate change. Badly needed is an observational system that will allow scientists 30 years from now to assess whether aerosol burdens have changed.

"Dominance of Mineral Dust in Aerosol Light-Scattering in the North Atlantic Trade Winds," X. Li (Sch. Marine & Atmos. Sci., Univ. Miami, 4600 Rickenbacker Causeway, Miami FL 33149), H. Maring et al., 416-419. Recent studies of the effect of dust on climate have focused on anthropogenic sulfate aerosols and have largely ignored mineral dust. Measurements reported here show that the net scattering of light by North African mineral dust delivered to Barbados by the trade winds is about four times that by non-seasalt sulfate aerosols. Mineral dust could be an important climate forcing agent over this ocean region and others. Although a natural substance, emissions of dust are increasing, in part from human activity.

"The Influence of Climate Forcing of Mineral Aerosols from Disturbed Soils," I. Tegen (Dept. Applied Phys., Columbia Univ., 2880 Broadway, New York NY 10025), A.A. Lacis, I. Fung, 419-422. Previous work has shown that a large fraction of tropospheric aerosol consists of wind-blown mineral dust originating from soils disturbed by human activity or by drought or rain. This study uses a radiative transfer model embedded in a general circulation model to show that dust from disturbed soils causes a decrease of the net surface radiation forcing of about 1 W m-2, accompanied by increased atmospheric heating that may be a significant forcing of atmospheric dynamics.

Item #d96may20

"Parameterizations of Marine Stratus Microphysics Based on In Situ Observations: Implications for GCMs," I. Gultepe (Cloud Phys. Res. Div., Atmos. Environ. Serv., 4905 Dufferin St., Downsview ON M3H 5T4, Can.), G.A. Isaac et al., J. Clim., 9(2), 345-357, Feb. 1996.

Airborne observations conducted in marine stratus over the east coast of Canada are used to develop cloud microphysical parameterizations schemes for general circulation models. Results show that multiple relationships are present among various microphysical properties, depending in part on variations in both aerosol concentrations and cloud dynamic activity. Parameterized equations must be used in GCMs with caution.

Item #d96may21

"How Much Solar Radiation Do Clouds Absorb?" Science, 271(5252), 1131-1136, Feb. 23, 1996.

Correspondence on two independent reports showing that clouds absorb much more solar radiation than predicted by theory, or than currently calculated in GCMs. (See related entries in Global Climate Change Digest, April 1995, in Prof. Pubs./Of General Interest/Clouds and Climate and Research News).

Item #d96may22

"On the Global Variation of Precipitating Layer Clouds," B.F. Ryan (Div. Atmos. Res., CSIRO, PMB 1, Aspendale, Victoria 3195, Australia), Bull. Amer. Meteor. Soc., 77(1), 53-69, Jan. 1996.

Presents a synthesis of observations of precipitating layer clouds around the world. The synthesis was conducted as part of the Global Energy and Water Cycle Experiment Cloud System Study, which aims to improve the treatment of cloud system processes in climate models. Identifies requirements for completing a systematic database of precipitating layer clouds.

Item #d96may23

"The Arctic Haze Phenomenon," G.E. Shaw (Geophys. Inst., Univ. Alaska, 903 Koyukuk Dr., Fairbanks AK 99775), Bull. Amer. Meteor. Soc., 76(12), 2403-2413, Dec. 1995.

A broad review and perspective emphasizing the discovery of Arctic haze pollution in the 1950s-1980s, which altered the prevailing view of the Arctic as a pristine region. Discusses climatic implications.

Item #d96may24

"Dimethyl Sulfide in the Arctic Atmosphere," R.J. Ferek (Dept. Atmos. Sci., Box 351640, Univ. Washington, Seattle WA 98195), P.V. Hobbs et al., J. Geophys. Res., 100(D12), 26,093-26104, Dec. 20, 1995.

Reports airborne and ground-based measurements showing that the Arctic Ocean is potentially a substantial source of DMS, which likely becomes important as sea ice melts in the early summer.

Item #d96may25

"Mission to Planet Earth: Role of Clouds and Radiation in Climate," B.A. Wielicki (Atmos. Sci. Div., NASA-Langley, MS-420, Hampton VA 23681), R.D. Cess et al., Bull. Amer. Meteor. Soc., 76(11), 2125-2153, Nov. 1995.

An extensive overview of the role played by NASA Earth Observing System (EOS) satellite data in understanding how clouds affect the global climate system. Planned EOS data products are summarized, including the critical advances over current satellite cloud and radiation budget data. EOS data are a necessary but insufficient condition for understanding this topic; a balanced approach of satellite, field and laboratory data will be required.