The first objective would contribute to a better understanding of the decadal and longer time scale climate forcing; the second would lead to improved coupled ocean-atmosphere models; and the third would aid the development of tropospheric chemistry models. The equatorial Indian Ocean during the northeast winter monsoon season is a unique natural laboratory for addressing these objectives. The selected experiment area is probably the only place in the world where an intense source of continental aerosols, anthropogenic trace species and their reaction products (e.g., sulfates and ozone) from the northern hemisphere is directly connected to the pristine air of the southern hemisphere by a cross equatorial monsoonal flow into the intertropical convergence zone (ITCZ). Furthermore, the deep convection within the ITCZ gives rise to extensive mid- and upper-level cloud systems.

The INDOEX composite observing system consists of four US aircraft (C-130 and WB-57 from NSF, ER-2 from NASA and P-3 from NOAA); a Dutch aircraft (Citation); a German research vessel (Sonne); an Indian research vessel (Sagar Kanya); French constant level balloons (LMD, Paris); 2 island stations, one at Malé and the other at Reunion/Mauritius; operational and research satellites; 4-D high resolution analyzed fields; and GCMs. The experimental period consists of a 4 month intensive field phase (IFP) that will begin on January 1, 1998 and enhanced observation phase (EOP) that will last 1 to 3 years depending on the platform. Research flights and cruises will last for 6 weeks during the IFP. Data will also be collected during ferry flight from the US. The composite observing system is designed to obtain regional (2.5 latitude x 2.5 longitude) estimates of several aerosol, radiation and chemistry related quantities over the Indian Ocean between 25šS to 20šN. In order to extend the field data to time and space scales relevant for climate, the observations from INDOEX will be integrated using the proven C⁴ Integrated Data System (CIDS). CIDS was designed to facilitate interdisciplinary research by providing a common interface to complex and heterogeneous data sets.

The integrated IFP data from CIDS should provide valuable "ground truth" for satellite experiments such as TRMM. The integrated 2 to 3 year data (from buoy, island stations, satellites and analyzed fields) can provide useful benchmarks for studies related to low frequency variability.

INDOEX is an international field experiment with participation from France, Germany, India, Netherlands, and the US. Their specific contributions include an aircraft, two research vessels, constant level balloons, instruments on US aircraft, an island station at Reunion, satellite data and 3-D models. The funds for these platforms are provided either through new proposals to the respective nations or through base funds to the respective PI institutions. This proposal constitutes the US component of INDOEX, and it will seek funding from NSF, DOE and NASA. The funds requested in this proposal constitute about 40% of the overall program. The total US component (including base funding to C⁴, NOAA-Aeronomy Laboratory and NCAR) is about 60%. In essence, the program outlined here leverages several ongoing national and international projects.