While CEPEX represents an outstanding contribution to our understanding of the regulation of tropical SST, many important questions remain in the climate conundrum. Guiding C4's ongoing research are two central and complimentary objectives. One is to identify and quantify the key processes that maintain tropospheric ozone and sulfate distribution in pristine and polluted environments. This is important because ozone and sulfates have significant affects on climate on decadal and centennial timescales. The other prime objective of C4 research is to characterize complex feedbacks among SST, deep convection, water-vapor greenhouse effect, and cirrus clouds. Such feedbacks are at the very core of the climate change conundrum.
Current and future research at C4 is guided by a pressing need to fill major gaps in existing initiatives dealing with cloud-chemistry-climate interactions. Applying a genuinely interdisciplinary and multi-institutional approach, C4 seeks to address a diverse set of needs, from improving cloud parameterizations in computerized general circulation models (GCMs) to providing information useful in the national policy arena. To fulfill this broad charge, a variety of C4 projects are planned or already underway which can be categorized into three objectives:
First Objective: Develop an atmospheric model for the tropical Pacific that includes sulfur and ozone chemistry, transport due to deep convection, microphysics, and chemistry on ice crystal surfaces.
Such a model will begin to provide answers to pivotal questions including:
Second Objective: Use the integrated CEPEX data to validate, develop, and improve general circulation model (GCM) parameterizations of clouds involving tropical con vective cirrus cloud systems.
The first step in this process is the previously mentioned comparison of several versions of NCAR CCM2 simulations for the CEPEX period with actual CEPEX observations. Specific comparisons will be made with respect to humidity, water vapor, surface energy budgets, cloud forcing at the surface and the tropopause, and the extent and frequency of mesoscale convective systems (MCS). The next step will be to focus on improving cloud parameterizations with respect to MCS and cirrus microphysical radiative effects.
In regard to MCS, key questions are:
For microphysical effects, key questions include:
Third Objective: A major observation program to test model predictions and empirical hypotheses for the clouds-chemistry-climate interactions, to culminate in a field cam paign in the Indian Ocean.
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, dynam ics, biology and human intervention. However, it has been very difficult to translate this awareness into action, in part because we lack observations of such interdiscipli nary phenomena. The equatorial Indian Ocean provides a unique natural laboratory for unraveling problems at the intersection of these various disciplines.
The selected experiment area, west-southwest of the Indian subcontinent, is probably the only place in the world where an intense source of continental aerosols, anthropo genic trace species and their reaction products (e.g., sulfate, ozone) from the northern hemisphere is directly connected to the pristine air of the southern hemisphere by a cross equatorial monsoonal flow into the inter tropical 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 observations on both sides of the ITCZ will provide data to assess:
Above all, the subcontinent 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.
V. Ramanathan, Jim Coakley, Russ Dickerson, and Andy Heymsfield will lead the US effort, while Paul Crutzen, Dieter Kley and Jos Lelieveld will coordinate the European programs.