High-Resolution Image

The figure shows the annual mean aerosol optical depth at 550 nm (AOD), calculated from daily MODIS 10 km retrievals. The algorithm used to derived these AOD is the new Collection 005 code, which represents a major change from previous collections. Note that the standard MODIS algorithm does not retrieve over clouds, or over snow, ice, sun glint or bright desert surfaces. Thus, the aerosol distribution of the figure is biased toward summer retrievals in high latitude and cloud-free high pressure systems, while totally missing bright desert surfaces.

The global aerosol system in 2006 was both typical and atypical of long standing patterns. We see that in 2006 western central Africa and the adjoining Atlantic ocean, the Indo-Gangetic basin in India and northeastern China continue to demonstrate strong aerosol loading as in previous years. Indonesia has unusually high annual mean aerosol loading in 2006. The heavy aerosol loading over eastern Russia and Siberia that appears to intensify over the Arctic Ocean was caused by biomass burning of agricultural lands and boreal forest in Russia during May and transported across Scandinavia and into the Arctic. The MODIS picture is slightly misleading. Because of snow and ice cover, MODIS retrievals are possible only in a limited part of the year. An aerosol event that occurs in the short summer season will be exaggerated in the annual mean values. Only moderate amounts of aerosol are seen over western Europe and eastern North America, even though these regions are thought to produce sulfate and carbonaceous particulate pollution. The Amazon Basin also shows only moderate aerosol loading, although expectations of strong biomass burning would suggest higher values of AOD. Most of the aerosol seen over the ocean in the figure is transported from continental sources. However, the ocean also produces sea salt and dimethylsulfide (DMS) particles. Thus, sometimes land areas report lower values of AOD than surrounding oceans.

Image was created by Reto Stockli of the Earth Observatory. Text by Lorraine Remer.