NCAR Scientists, Aircraft, Instruments Head To Indian Ocean For Climate ChangeExperiment; UCAR Directs ...( and acid rain. Kiehl helped desi...)

Kiehl helped design INDOEX to ensure that the project collects the data needed to advance global climate modeling. Some physical and chemical processes in the earth system are so complicated that modelers cannot simulate each detailed step. "With INDOEX data, we can actually test the way we treat aerosols in computer models against observations."

The observation region is downwind of the Indian subcontinent during the spring and extends into the pristine Southern Hemisphere. With a forecast of pleasant weather--calm, with little rain--the investigators should be able to sample both polluted and clean air in clouds and clear sky.

"It's a natural laboratory for studying direct and indirect effects of aerosols," says NCAR's Andrew Heymsfield, another INDOEX researcher. The direct effect of aerosols is the scattering that occurs when solar radiation bounces off particles in clear air. The indirect effects have to do with sulfates' interactions with clouds.

Globally, aerosols are an important source of nuclei around which cloud droplets can condense, and in the tropics they are the chief source. The more cloud condensation nuclei, the brighter the cloud, that is, the more solar radiation reflected back into space before it reaches the earth's surface. This radiative effect is what makes clouds, and the indirect effects of aerosols, so important in climate change research. However, indirect effects are now so little understood that estimates in global climate models vary from almost no effect to more than enough cooling to offset global warming resulting from greenhouse gas increases.

"A host of changes in cloud physical and microphysical properties are lumped under the term 'indirect effects,' " says NCAR scientist William Collins. Collins is using satellite measurements to estimate optical depths in clouds and the sizes of aerosol droplets.

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Contact: Anatta
anatta@ucar.edu
303-497-8604
National Center for Atmospheric Research/University Corporation for Atmospheric Research
4-Mar-1999