This presentation will provide a preview of the NASA/GMAO atmospheric global reanalysis project called the Modern Era Retrospective- Analysis for Research and Applications (MERRA).

MERRA is based on a major new version of the Goddard Earth Observing System Atmospheric Data Assimilation System (GEOS-5 ADAS), that includes the ESMF-based GEOS-5 AGCM and the new NCEP grid-point statistical interpolation (GSI) analysis scheme developed as a collaborative effort between NCEP and the GMAO. Model and analysis resolution is ? degrees longitude by ½ degree latitude with 72 levels extending to 0.01 hPa. The MERRA time period will cover the modern era of remotely sensed data, from 1979 through the present, and the special focus of the atmospheric assimilation will be the hydrological cycle. MERRA products will comprise a suite of prognostic and diagnostic fields including comprehensive sets of cloud, radiation, hydrological cycle, ozone, and land surface diagnostics. A special collection of data files are designed to facilitate off-line forcing of chemistry/aerosol models.

Previous long-term reanalyses of the Earth's climate had high levels of uncertainty in precipitation and inter-annual variability. The GEOS5 data assimilation system to be used for MERRA implements Incremental Analysis Updates (IAU) to slowly adjust the model states toward the observed state. The water cycle benefits as unrealistic spin down is minimized. In addition, the model physical parameterizations have been tested and evaluated with data assimilation present which also reduces the shock of adjusting the model system. Along with the Catchment land surface model, MERRA is anticipated to improve upon the representation of the water cycle in reanalyses.