BOULDER--How much do sulfate aerosols--a form of pollution--cool theclimate? That's one of the most pressing questions for understandingglobal climate change. To help find the answer, the National Center forAtmospheric Research (NCAR) has sent researchers, instruments, and a C-130 research aircraft owned by the National Science Foundation (NSF) tothe $25-million Indian Ocean Experiment (INDOEX). NSF is NCAR's primarysponsor and a partial sponsor of INDOEX.
INDOEX is based in the Republic of the Maldives, an archipelagosouthwest of India's southern tip. There, NCAR scientists are workingalongside more than 70 researchers from a dozen nations to observe thetropical oceans and atmosphere from January to April. The UniversityCorporation for Atmospheric Research, NCAR's parent organization, isoverseeing operations from its support office for logistics and datamanagement, headed by Richard Dirks of the UCAR Office of Programs. Thehighly instrumented C-130 aircraft will be based through March 27 atMale' airport, which occupies its own island in the archipelago.
According to NCAR's Jeffrey Kiehl, a principal investigator for INDOEX,"In the future, pollution in the tropics will increase, so we'd betterunderstand it now. The chemistry in the tropics is severelyundersampled." The Indian subcontinent and surrounding nations are richsources for many kinds of aerosols, including those produced fromindustrial and auto emissions, biomass burning, and soil dust. WithAsia's population rising at a dramatic rate, the amount of sulfurdioxide released into the atmosphere is expected to increase. Sulfurdioxide is converted into sulfate aerosol in the atmosphere.
The ability of sulfate aerosols to reflect the sun's radiation may beone reason that increasing greenhouse gases have not warmed the earth asmuch as some climate models have predicted. Sulfates also contribute tolocal pollution and acid rain.
Kiehl helped design INDOEX to ensure that the project collects the dataneeded to advance global climate modeling. Some physical and chemicalprocesses in the earth system are so complicated that modelers cannotsimulate each detailed step. "With INDOEX data, we can actually test theway we treat aerosols in computer models against observations."
The observation region is downwind of the Indian subcontinent during thespring and extends into the pristine Southern Hemisphere. With aforecast of pleasant weather--calm, with little rain--the investigatorsshould be able to sample both polluted and clean air in clouds and clearsky.
"It's a natural laboratory for studying direct and indirect effects ofaerosols," says NCAR's Andrew Heymsfield, another INDOEX researcher. Thedirect effect of aerosols is the scattering that occurs when solarradiation bounces off particles in clear air. The indirect effects haveto do with sulfates' interactions with clouds.
Globally, aerosols are an important source of nuclei around which clouddroplets can condense, and in the tropics they are the chief source. Themore cloud condensation nuclei, the brighter the cloud, that is, themore solar radiation reflected back into space before it reaches theearth's surface. This radiative effect is what makes clouds, and theindirect effects of aerosols, so important in climate change research.However, indirect effects are now so little understood that estimates inglobal climate models vary from almost no effect to more than enoughcooling to offset global warming resulting from greenhouse gasincreases.
"A host of changes in cloud physical and microphysical properties arelumped under the term 'indirect effects,' " says NCAR scientist WilliamCollins. Collins is using satellite measurements to estimate opticaldepths in clouds and the sizes of aerosol droplets.
The Maldives archipelago runs in a north-south line from about 500 milessouthwest of the tip of the Indian subcontinent to the equator. Thepersonnel and observing systems are spread across several islands, withall transport by boat. Resources include five aircraft, two researchships, and a host of ground-based systems. Satellite data will be usedfor real-time weather forecasting, monitoring the motion of pollutants,and measuring radiation at different altitudes. This combination ofground, airborne, and satellite data is expected to vastly increasescientists' understanding of the nature and scope of aerosols' indirecteffects.
Heymsfield and NCAR colleague Gregory McFarquhar are studying some ofthe cloud microphysical changes using a scanning aerosol backscatterlidar, developed at NCAR and mounted on the C-130. From the aircraft thelidar can characterize cloud top and bottom. The scientists will observethe optical depth of clouds in both clear and cloudy aerosol-ladenskies.
"The government of the Maldives has been extraordinarily cooperative andaccommodating," says Dirks. "They're deeply concerned with climatechange research." The Maldives islands are vulnerable to rising sealevels due to climate change.
INDOEX is coordinated by the Center for Clouds, Chemistry and Climate(C4), an NSF Science and Technology Center at the Scripps Institution ofOceanography. Paul J. Crutzen, director of the Max Planck Institute forChemistry and a 1995 Nobel Laureate in Chemistry, and C4 director V.Ramanathan will serve as INDOEX chief scientists.
Note to Editors: Please contact Anatta (information above) tointerview INDOEX participants or to fly on the C-130 aircraft.For more information, see the INDOEX Web site: http://www-indoex.ucsd.edu/
Find this news release on the World Wide Web at http://www.ucar.edu/publications/newsreleases/1999/INDOEX.html
The above story is based on materials provided by University Corporation For Atmospheric Research. Note: Materials may be edited for content and length.
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