The Modern Era Retrospective-Analysis for Research and Applications (MERRA) was undertaken by NASA’s Global Modeling and Assimilation Office with two primary objectives: to place observations from NASA’s Earth Observing System satellites into a climate context and to improve upon the hydrologic cycle represented in earlier generations of reanalyses. MERRA was generated with version 5.2.0 of the Goddard Earth Observing System (GEOS) atmospheric model and data assimilation system (DAS), and covers the modern satellite era from 1979 to the present. Specifically, the GEOS-DAS Version 5 implements Incremental Analysis Updates (IAU) to slowly adjust the model states toward the observed state.
The summary information was written with help from Richard Cullather. Any errors are ours.
MERRA FAQ 6: Why are there such large discrepancies at 1000mb and 850mb bewtween MERRA and other reanalyses?
The GEOS5 data assimilation system used to produce MERRA does not (or did not at the time of production) extrapolate data to pressure levels greater than the surface pressure. These grid points are marked by undefined values. The result is that area averages that include these points will not be representative compared to other data sets without additional screening. Time averages, such as monthly means, may also have substantial differences at the edges of topography. The lowest model level data and surface data are available so that users can produce their own extrapolation. A page discussing this issue is available. See http://gmao.gsfc.nasa.gov/research/merra/pressure_surface.php
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|Taylor diagrams of annual mean precipitation from reanalyses using GPCP and CMAP as observing references. Red and blue lines show limits of expected high and low correlation determined by comparing GPCP and CMAP. From Bosilovich et al. (2011) and contributed by R. Cullather.|
|Climatological (1989-2010) total water vapor for January and July. [Climate Data Guide; D. Shea]|
|Latitude-pressure cross section of mean zonal wind at 210E for January 2010. The black filled areas indicate topography. [Climate Data Guide; D. Shea]|
|Longitude-pressure cross section of mean meridional wind at 45N for January 2010. The black filled areas indicate topography. [Climate Data Guide; D. Shea]|
National Center for Atmospheric Research Staff (Eds). Last modified 31 May 2016. "The Climate Data Guide: NASA MERRA." Retrieved from https://climatedataguide.ucar.edu/climate-data/nasa-merra.