Aerosol Indirect Effect a Measurement Based Approach

Aerosol introduces one of the largest uncertainties in climate modeling. Among the aerosol impacts on the radiative energy balance it is usually distinguished between the impact directly associated with modifications to aerosol properties (the direct effect) and the impact of changes to other atmospheric properties due to aerosol modifications (indirect effects). Since clouds are the main modulators of our climate, particular important are aerosol associated changes to properties of clouds and to the hydrological cycle. Indirect effects are numerous. Some of them will `warm' (increase the energy to the EAS [Earth-Atmosphere-System]) and some of then will `cool' (decrease the energy to the EAS). The overall sign will vary with aerosol type and environmental conditions. Thus, quantifications on a global basis are anybody's guess. Our current understanding from global modeling tends toward `cooling'. However, it is unclear, if these models properly consider all relevant aerosol-cloud interactions or if effects of local studies can be extended to larger spatial (regional) or temporal scales (seasonal). Currently, uncertainties in aerosol indirect modeling are so large that measurement based approaches have become an option. New capabilities in remote sensing now provide not only simultaneous data on many properties for aerosol and clouds but also on radiative fluxes at the top of the atmosphere capturing changes to the EAS energy balance. Despite data restrictions in terms of spatial coverage and accuracy, now correlations between aerosol and clouds can provide clues to modelling where (region) and when (season) what aerosol indirect effect applies. And the energy balance data can even provide quantitative constraints to modeling on a regional and seasonal basis. Data from the MODIS, MISR and CERES sensors of NASA's EOS Terra platform are analyzed. Global maps of correlations between aerosol and cloud properties are presented and discussed and a measurement based quantification on the aerosol indirect effect will be provided.