Regional advanced very high resolution radiometer - Derived climatology of aerosol optical thickness and size

Abstract

We have used the NASA Global Energy and Water Cycle Experiment (GEWEX) Global Aerosol Climatology Project data set of retrieved aerosol optical thickness and Ångström exponent to construct and analyze regional aerosol climatologies for a number of areas affected by different aerosol types (such as dust, biomass burning, anthropogenic, or clear maritime aerosols) that exemplify the range of natural aerosol variation. We have found that variations in the number of individual pixels used to calculate monthly means associated with short- and long-term satellite orbit changes and instrument degradation have little effect on global and hemispherical values of the aerosol optical thickness and Ångström exponent. Aerosol loads are found to be higher, and aerosol particles smaller, over the northern Atlantic Ocean off the coast of Europe and the eastern United States, rather than off the west coast, thereby indicating a significant impact of anthropogenic aerosols. The smallest background levels of maritime aerosols are found in the southern Pacific Ocean, with seasonal mean optical thicknesses as low as 0.1. We analyze time series of the aerosol optical thickness in the regions affected by dust outflows from the Sahara and Asian deserts and by biomass burning. An influence of anthropogenic aerosols associated with the high regional industrial activity is apparent in the eastern China Sea. Two distinct periods are identified in satellite and Sun photometer aerosol time series over the Black Sea with transition time around 1993. During the first period the aerosol loads in the region significantly exceeded the hemispherical mean, whereas in the second period they became very close. This change is linked to the reduction of the industrial output in that region. Copyright 2005 by the American Geophysical Union.