NASA MERRA

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The original MERRA has been replaced by MERRA-2.

Key Strengths

Significant improvement in precipitation and water vapor climatology over older reanalyses

The IAU procedure in which the analysis correction is applied to the forecast model gradually ameliorates precipitation spin-down during early stages of the forecast, and allows for higher frequency output including selected hourly fields

Provides vertical integrals and analysis increment fields for the closure of atmospheric budgets

Key Limitations

Changes in the observing system strongly affect trends in many fields (as for other reanalyses); for example P-E exhibits spurious increases associated with assimilating radiances from the AMSU starting in 1998 and to a lesser extent, SSM/I in 1987

Spatial discontinuity in central African moisture fields associated with rawinsonde input

The assimilation routine is “frozen” and will not be updated for newer satellite instruments, so quality will eventually degrade as current instruments expire

Please cite data sources, following the data providers' instructions

Dataset DOIs

None

Hosted Climate Index Files

None

Data Access

Usage Restrictions

Research

Expert Developer Guidance

The summary information was written with help from Richard Cullather. Any errors are ours.

Cite this page

Acknowledgement of any material taken from or knowledge gained from this page is appreciated:

National Center for Atmospheric Research Staff (Eds). Last modified 2025-12-11 "The Climate Data Guide: NASA MERRA.” Retrieved from https://climatedataguide.ucar.edu/climate-data/nasa-merra on 2026-03-16.

Citation of datasets is separate and should be done according to the data providers' instructions. If known to us, data citation instructions are given in the Data Access section, above.

Acknowledgement of the Climate Data Guide project is also appreciated:

Schneider, D. P., C. Deser, J. Fasullo, and K. E. Trenberth, 2013: Climate Data Guide Spurs Discovery and Understanding. Eos Trans. AGU, 94, 121–122, https://doi.org/10.1002/2013eo130001

Key Figures

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]