The Global Tropospheric Aerosol
The oceanic satellite observations reveal that the global tropospheric aerosol is a collection of largely independent aerosol regions, each having a bio-geochemically active source and unique spatial temporal pattern. There is no evidence for a ubiquitous "global aerosol" that fills the troposphere with a uniform, background aerosol. The characteristics of this heterogeneous aerosol mixture and some of their implications include:
- Marine aerosols dominate large zonal belts in the summer hemispheres but, continental aerosol plumes show more intense oceanic backscattering. Hence, the aerosol backscattering over the continents are likely to be much higher than over the oceans.
- The aerosol backscattering is strongest at near-tropical latitudes (0-30) where most of the solar radiation is absorbed and aerosol-cloud interactions are intense.
- There is a pronounced seasonality in each aerosol region; the higher aerosol levels appear in the summer hemispheres although many continental and marine aerosol regions show a spring maximum. Models that aim at simulating the global aerosol sources and dispersion pattern need to reproduce the observed spatial pattern as well as the seasonality.
- The spatial-temporal aerosol pattern presented here and throughout the literature reveals an intriguing dynamic behavior that is probably unparalleled in atmospheric chemistry (38). Hence, the full characterization of the global aerosols requires several descriptive variables (39), a horizontal scale on the order of 100 km, a temporal resolution of a month or less, and a vertical resolution that is yet to be determined.
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