Scientific rationale of the project

Environmental hazards in the form of air pollution, floods, and droughts affect a large part of the world's population. The atmospheric aerosol is an important contributor to air pollution, and is thought to play a role in determining important features of the hydrological cycle and other aspects of the climate system. The properties, amount and distribution of the atmospheric aerosol have changed greatly as a byproduct of industrialization and the accompanying explosion in human population. Recent studies suggest that increased aerosol loading, most evident at the regional scale, has changed the balance of radiant energy within the climate system and altered the hydrological cycle in ways that make the climate system more conducive to precipitation extremes.

Unfortunately, more definitive statements about the effects of changes in the atmospheric aerosol are limited by our incomplete understanding of the interplay between the aerosol, clouds and precipitation. This remains the principal barrier to advancing our ability to quantify the impact of the aerosol on precipitation and circulation systems from local to global scales. Hence, developing our understanding of this interplay is not just a major scientific challenge, but is also essential to the development of strategies for both adapting to, and mitigating, the effects of climate change.

New measurement and modeling capabilities provide unprecedented opportunities for studying aerosol-cloud-precipitation interactions. The advance in remote sensing (both space- and surface- based) is providing an unprecedented view of cloud micro and macro structure, and surface rain rates across a range of space and time scales. When combined with surface networks of multi- parameter and multi-wavelength radars, lidars, and microwave radiometers, for example, the opportunities are staggering. A good example of remote sensing capabilities is the A?Train of satellites providing vertical profiles of aerosol, clouds and precipitation. Wealth of satellite based data is available but under-exploited.

For the first time, the forthcoming Intergovernmental Panel on Climate Change (IPCC) Assessment Report 5 will contain a separate chapter on the role of aerosols and clouds in the climate system. The work performed by this ISSI Team will be included in the IPCC report.