The MERRA-2 Aerosol Reanalysis, 1980 - onward, Part I: System Description and Data Assimilation Evaluation

Area of Science:

• Earth System Science
• Atmospheric Science
• Climate Modeling

Background:

• The Modern-Era Retrospective Analysis for Research and Applications, Version 2 (MERRA-2) is an updated NASA reanalysis system.
• MERRA-2 incorporates improved Earth system modeling (GEOS-5) and additional observational data.

Purpose of the Study:

• To document the MERRA-2 aerosol assimilation process, including model description, emissions, and data quality control.
• To validate MERRA-2 aerosol optical depth (AOD) fields using independent observations.
• To assess the impact of AOD assimilation on aerosol simulations and examine aerosol-climate interactions.

Main Methods:

• Description of the GEOS-5 coupled to GOCART aerosol module.
• Assimilation of aerosol optical depth (AOD) from ground- and space-based remote sensing.
• Validation of analyzed AOD using independent ground, aircraft, and shipborne data.
• Comparison of MERRA-2 aerosol fields with a control simulation lacking AOD assimilation.

Main Results:

• MERRA-2 successfully assimilates aerosol optical depth (AOD) data.
• AOD assimilation positively impacts simulated aerosol fields.
• Initial evaluation of aerosol-climate interactions, specifically the shortwave, clear-sky aerosol direct radiative effect, is presented.

Conclusions:

• MERRA-2 provides a valuable new reanalysis product for aerosol research.
• The study highlights the skill of MERRA-2 aerosol assimilation products.
• Caveats for using MERRA-2 in future aerosol-climate interaction studies are identified.