The Stratosphere in MERRA and MERRA-2

Steven Pawson, NASA Goddard Space Flight Center, Global Modeling and Assimilation Office, Greenbelt, United States, Lawrence Coy, NASA GSFC and SSAI, Greenbelt, United States, Krzysztof Wargan, SSAI at NASA GSFC, Greenbelt, MD, United States and Will McCarty, NASA Goddard Space Flight Center, Greenbelt, MD, United States
Abstract:
This paper focuses on the middle atmosphere in reanalyses performed using the GEOS-5 data assimilation system, emphasizing the impacts of fairly major changes in the underlying model, the details of the analysis scheme, and the choice of datasets that are included. The Modern-Era Retrospective analysis for Research and Applications (MERRA) dataset is quite widely documented and used. Substantial improvements to the GEOS-5 system since the MERRA version was frozen (about five years ago) motivate the production of a successor dataset, MERRA-2: a major consideration, though, is the fact that MERRA cannot ingest the most recent data types, such as IASI, GPS-RO, whose value is demonstrated by the more recent versions of GEOS-5 run in near-real time. Aspects to address are how the following changes impact the middle atmosphere: updates to the GCM, especially a new representation of gravity wave drag; use of a different radiation transfer model for the Stratospheric Sounding Unit radiances; introduction of GPS-RO datasets into MERRA-2; the choice of using the EOS-Aura Microwave Limb Sounder temperature and ozone fields after 2004. The impacts of these datasets will be shown using suitable examples.
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