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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The original MERRA has been replaced by MERRA-2.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

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

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

Expert Developer Guidance

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 "The Climate Data Guide: NASA MERRA.” Retrieved from on 2024-04-17.

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,

Key Figures

Climate Data Guide Image

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.

Climate Data Guide Image

Climatological (1989-2010) total water vapor for January and July. [Climate Data Guide; D. Shea]

Climate Data Guide Image

Latitude-pressure cross section of mean zonal wind at 210E for January 2010. The black filled areas indicate topography. [Climate Data Guide; D. Shea]

Climate Data Guide Image

Longitude-pressure cross section of mean meridional wind at 45N for January 2010. The black filled areas indicate topography. [Climate Data Guide; D. Shea]

Other Information

Years of record
Data time period extended
Yes, data set is extended
Sub-daily, Monthly
Input Data
Vertical Levels:
Missing Data Flag
Depends on variable
Ocean or Land
Ocean & Land
Spatial Resolution

0.5° x 0.667° x 72 , 0.01 hPA top

Model Resolution (reanalysis)

0.5° x 0.667° x 72

Data Assimilation Method
Model Vintage (reanalysis)