The Stratosphere in MERRA and MERRA-2

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.