The Modern-Era Retrospective Analysis for Research and Applications, Version 2: The Goddard Aerosol Assimilation System Aerosol Reanalysis 1979 — Present

The Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) was undertaken by NASA's Global Modeling and Assimilation Office (GMAO) with two primary objectives: to place observations from NASA's Earth Observing System (EOS) satellites into a climate context and to update the Modern-Era Retrospective analysis for Research and Applications (MERRA) system to include the most recent satellite data. Numerous advancements have been incorporated into the MERRA-2 system, such as an improved balance between precipitation and evaporation and a reduction of the impact of a changing observing system on the analysis. Of relevance to this presentation, and as a significant step towards an Integrated Earth System Analysis (IESA), MERRA-2 now includes fully modeled and analyzed aerosol fields, with radiative effects that feed back to the atmosphere. Focusing on the satellite era, from 1979 to the present, MERRA-2 uses an online implementation of the Goddard Chemistry, Aerosol, Radiation, and Transport model (GOCART) integrated into the Goddard Earth Observing System Model, Version 5 (GEOS-5) modeling system. GOCART simulates organic carbon, black carbon, sea salt, dust, sulfate and sulfate aerosol precursors (dimethyl sulfide, sulfur dioxide), carbon monoxide and carbon dioxide. While the original MERRA assimilated only meteorological parameters (winds, temperature, humidity, etc.), with the Goddard Aerosol Assimilation System (GAAS), we now extend MERRA-2 to include assimilation of bias-corrected Aerosol Optical Depth (AOD) retrievals from AVHRR, MODIS, MISR (over bright surfaces), and AERONET. Here we present an overview of the MERRA-2 aerosol assimilation product, including an assessment of its overall performance relative to numerous independent aerosol observations from remote sensing platforms, ground-based stations, and aircraft. We also present the overall climatology and time series of AOD from 1979 - present, and we explore the impact of major volcanic eruptions (e.g. Pinatubo) on the analyzed aerosol fields.