The MERRA-2 Aerosol Reanalysis, 1980 Onward. Part II: Evaluation and Case Studies

Area of Science:

• Atmospheric Science
• Earth System Science
• Climate Modeling

Background:

• The Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2) is NASA's latest reanalysis dataset.
• MERRA-2 incorporates aerosol assimilation, a key improvement over its predecessor, MERRA-1.

Purpose of the Study:

• To assess the quality and performance of MERRA-2 aerosol products.
• To evaluate MERRA-2's aerosol optical depth (AOD) assimilation against independent observations.
• To identify strengths and limitations of MERRA-2 aerosol data.

Main Methods:

• Comparison of MERRA-2 absorption aerosol optical depth (AAOD) and ultraviolet aerosol index (AI) with Ozone Monitoring Instrument (OMI) data.
• Evaluation of MERRA-2 aerosol vertical structure and surface particulate matter (PM2.5) using satellite, aircraft, and ground-based observations.
• Case studies of major aerosol events (e.g., Mount Pinatubo, Saharan dust, wildfires, pollution) to analyze AOD assimilation.

Main Results:

• MERRA-2 AAOD and AI show good agreement with OMI observations.
• MERRA-2 generally compares well with independent data for aerosol vertical structure and PM2.5, though model deficiencies (e.g., emissions) introduce biases.
• Assimilation of aerosol optical depth (AOD) in MERRA-2 demonstrates both successes and limitations during significant aerosol events.

Conclusions:

• MERRA-2 provides valuable aerosol data for climate research.
• Understanding model limitations is crucial for interpreting MERRA-2 aerosol products.
• Best practices for utilizing MERRA-2 aerosol reanalysis in future studies are recommended.