The MERRA-2 Aerosol Reanalysis

Abstract:

MERRA-2 is NASA's latest reanalysis for the satellite era (1980-present) using GEOS-5 earth system model. This project focuses on historical analyses of the hydrological cycle on a broad range of weather and climate time scales, and includes interactive aerosols for the entire period. MERRA-2 provides several improvements over its predecessor MERRA reanalysis, including: 1) modern satellite observing systems not available with MERRA, 2) reduction in discontinuities associated with a changing observing system, and 3) reduced biases and imbalances in the hydrologic cycle. As another step towards an integrated Earth System Analysis (IESA), MERRA-2 includes for the first time aerosols in a reanalysis, improves the representation of stratospheric ozone, and better characterizes cryospheric processes.

In this talk we will present results relating to the introduction of aerosols in MERRA-2. The assimilation of Aerosol Optical Depth (AOD) in GEOS-5 involves very careful cloud screening and homogenization of the observing system by means of a Neural Net scheme that translates MODIS and AVHRR radiances into AERONET calibrated AOD. The system also assimilates MISR and AERONET AOD observations. For the EOS period (2000-present) GEOS-5 is driven by daily biomass burning emissions derived from MODIS fire radiative power retrievals using the so-called QFED emissions. Historical emissions are calibrated as to minimize discontinuities the EOS/pre-EOS boundaries. MERRA-2 aerosols are also driven by historical anthropogenic and volcanic emissions.

We will present a summary of our efforts to validate the MERRA-2 aerosols. The GEOS-5 assimilated aerosol fields are first validated by comparison to independent in-situ measurements. In order to assess aerosol absorption on a global scale, we perform a detailed radiative transfer calculation to simulate the UV aerosol index, comparing our results to OMI measurements. By simulating aerosol-attenuated backscatter, we use CALIPSO measurements to evaluate the vertical structure of our aerosol estimates, in particular in regions where we have larger discrepancies with OMI. Finally, the consistency of our AOD estimates with estimates from MODIS/Deep Blue, OMI and PARASOL will be briefly discussed.