Retrieving global aerosol sources from satellites using inverse modeling

[摘要] Understanding aerosol effects on global climate requires knowing the global distributionof tropospheric aerosols. By accounting for aerosol sources, transports, and removalprocesses, chemical transport models simulate the global aerosol distribution usingarchived meteorological fields. We develop an algorithm for retrieving global aerosolsources from satellite observations of aerosol distribution by inverting the GOCART aerosol transport model.

The inversion is based on a generalized, multi-term least-squares-type fitting,allowing flexible selection and refinement of a priori algorithm constraints.For example, limitations can be placed on retrieved quantity partial derivatives,to constrain global aerosol emission space and time variability in the results.Similarities and differences between commonly used inverse modeling and remote sensingtechniques are analyzed. To retain the high space and time resolution of long-period,global observational records, the algorithm is expressed using adjoint operators.

Successful global aerosol emission retrievals at 2°×2.5 resolutionwere obtained by inverting GOCART aerosol transport model output, assuming constantemissions over the diurnal cycle, and neglecting aerosol compositional differences.In addition, fine and coarse mode aerosol emission sources were inverted separatelyfrom MODIS fine and coarse mode aerosol optical thickness data, respectively. Theseassumptions are justified, based on observational coverage and accuracy limitations,producing valuable aerosol source locations and emission strengths. From two weeksof daily MODIS observations during August 2000, the global placement of fine modeaerosol sources agreed with available independent knowledge, even though the inversemethod did not use any a priori information about aerosol sources, and was initializedwith a "zero aerosol emission" assumption. Retrieving coarse mode aerosol emissions wasless successful, mainly because MODIS aerosol data over highly reflecting desert dustsources is lacking.

The broader implications of applying our approach are also discussed.

[学科分类] 大气科学