FIGURE 4.11 These 19 global panels show the seasonal average distribution of atmospheric aerosol amounts across Africa and the Atlantic Ocean. The measurements capture airborne particles in the entire atmospheric column, for subvisible sizes ranging from tiny smoke particles to “medium” dust (about 0.5 to 2.5 microns). Such particles are produced by forest fires, deserts, volcanoes, breaking ocean waves, and urban and industrial pollution sources. SOURCE: NASA, GSFC, Langley Research Center (LaRC), Jet Propulsion Laboratory (JPL), Multiangle Imaging Spectroradimeter (MISR) Team.

Space observations have the potential to allow the estimation of the global average optical depth of aerosols, which is presently unknown. Rapid global coverage also allows sources of aerosols to be inferred from plumes of aerosols that can be observed over the oceans (Herman et al. 1997, Husar et al. 1997). Multiyear records of aerosol optical depth over water show reproducible seasonal patterns (Torres et al. 2002). Measurements from space show a surprisingly large contribution from Saharan dust and biomass burning and distinct differences between the northern and southern hemispheres, presumably due to human production of aerosols (Husar et al. 1997, Prospero et al. 2002).

The ability to distinguish aerosols from clouds and fine aerosols from coarse aerosols combined with the ability to construct a long-term record of aerosols is a remarkable accomplishment and demonstrates how sophisticated satellite technology and analysis tools have become. This newly gained observational capability greatly enhances our understanding of climate forcing by aerosols from natural and anthropogenic sources and leads to improvements in climate modeling.