Executive Summary

It has been known for nearly a decade that the outstanding problems in global change are those at the intersection of the various disciplines of physics, chemistry, dynamics, biology and human intervention. However, it has been very difficult to translate this awareness into action, in part because we lack observations of such interdisciplinary phenomena. The equatorial Indian Ocean provides a unique natural laboratory for unraveling problems at the intersection of these various disciplines. In this white paper we articulate the relevant scientific issues for an experiment in this region.

The selected experiment area, as indicated on the cover, is probably the only place in the world where an intense source of continental aerosols, anthropogenic trace spieces and their reaction products (e.g., sulfate, ozone) from the northern hemisphere, i.e., the Indian subcontinent, is directly connected to the pristine air of the southern hemisphere by a cross equatorial monsoonal flow into the intertropical convergence zone (ITCZ). By providing the confluence of the two contrasting air masses, the ITCZ can strengthen the north-south gradients in aerosols and gases. It can also distribute the pollutants and aerosol laden air vertically and horizontally. These are optimal conditions for testing:

* the aerosol cooling hypothesis that anthropogenic emissions of sulfur and other aerosol-forming compounds may lead to radiative cooling comparable in magnitude to greenhouse warming.

* the role of the ITCZ in the inter-hemispheric transport of trace gases and pollutants including resulting effects on tropospheric ozone

The observations on both sides of the ITCZ will provide data to assess:

* the role of continental and marine aerosols in the radiative forcing of remote oceanic regions

* the magnitude and physics of the excess solar absorption in ITCZ cloud systems

* the water vapor distribution and its greenhouse effect, and the role of clouds and evaporation in the Indian ocean's warm pool heat budget

Above all, the sub-continent is projected to be a major contributor to the emission of aerosols and reactive gases during the next century. The chemical, radiation, micro physical and meteorological data collected during INDOEX would serve as a baseline for assessing the changes in the coming decades.