MERRA¶
Modern-Era Retrospective analysis for Research and Applications
Discontinued
No longer updated
Production ended in March 2016; the analyses for February 29, 2016 are the last. GMAO states that its MERRA pages are no longer under development. As of 2026-10-11 the files are still on the GES DISC on-premises server (goldsmr1), but GES DISC has announced that on-premises HTTPS access ends by September 30, 2026, and the original MERRA collections could not be found in the Earthdata Cloud catalogue (CMR). Download any files you need now, and use MERRA-2 for new work.
Successor: MERRA-2 — 1980–present, 0.5° × 0.625° grid, 72 levels. Adds assimilation of satellite aerosol observations and observation-corrected precipitation forcing. Reference: Gelaro et al. (2017), J. Climate, 30, 5419–5454, doi:10.1175/JCLI-D-16-0758.1
At a glance¶
| Item | Details |
|---|---|
| Section | Atmosphere › Reanalyses |
| Type | Reanalysis |
| Domains | Atmosphere, Land |
| Provider | NASA Global Modeling and Assimilation Office (GMAO) / distributed by NASA GES DISC |
| Period | 1979-01 ~ 2016-02 |
| Coverage | Global |
| Horizontal resolution | Native grid 1/2° latitude × 2/3° longitude (540 × 361) / reduced grid 1.25° × 1.25° (288 × 144) |
| Vertical resolution | 72 model levels (top at 0.01 hPa) / 42 pressure levels |
| Temporal resolution | Hourly (2D diagnostics), 3- and 6-hourly (3D), monthly means |
| Update frequency | Ended (March 2016) |
| Licence | NASA open data (no restrictions on use); acknowledgement of GMAO and GES DISC requested |
| Account required | Yes |
Note on period: Production ended with the analyses for February 29, 2016 (GMAO announcement, 2016-03-14).
How to read the resolution
- Horizontal resolution lists both the native model grid and the grid you download, as given in the official documentation. The same dataset can come on different grids from different providers or products, so check the grid of your downloaded file.
- Grid spacing is not the effective resolution. A provided grid that is finer than the native one carries no extra information.
- Intervals and whether a value is instantaneous, mean or accumulated differ between variables — see 'Available variables' below.
- The 'provided resolution' in lists and the comparison table is a simplified km/degree value for quick comparison. Use this page for exact values.
Overview¶
MERRA is NASA GMAO's satellite-era global reanalysis, based on a version of the GEOS-5 atmospheric data assimilation system that was frozen in 2008, and released in 2009. A major goal was a better representation of the hydrological cycle, and its hourly 2D diagnostics gave it unusually high time resolution for its day. It has been superseded by MERRA-2 and is now used mainly to reproduce earlier studies and for comparisons across reanalysis generations.
What changes with the successor¶
MERRA → MERRA-2¶
Transition: 2016-02
MERRA used GEOS-5.2.0, frozen in 2008, and could not ingest observations from satellites launched after NOAA-18 (2005). GMAO produced MERRA-2 with GEOS-5.12.4 to fill that gap, adding a cubed-sphere grid, aerosol assimilation, dry-mass and water-budget constraints, and observation-corrected precipitation forcing. MERRA production stopped after the analyses for February 29, 2016.
| Aspect | MERRA | MERRA-2 |
|---|---|---|
| Period | 1979-01 to 2016-02 (ended) | 1980-01 to present (updated monthly, released around the 15th–20th of the following month) |
| System version | GEOS-5.2.0 (frozen in 2008) | GEOS-5.12.4 |
| Model and output grids | Latitude–longitude grid, output at 1/2° × 2/3° (540 × 361), 72 levels (top at 0.01 hPa) | Cubed-sphere grid (removes the polar grid singularity), output at 0.5° × 0.625° (576 × 361), 72 levels |
| Observations | Only satellites up to NOAA-18 (2005) could be assimilated; about 1.5 million observations per 6 hours | Adds IASI, CrIS and ATMS radiances, GPS radio occultation bending angles, MLS and OMI ozone, AVHRR atmospheric motion vectors, ASCAT and WindSat ocean surface winds and more. About 2 million (2002) to about 5 million (2015) observations per 6 hours |
| Radiative transfer model | Early CRTM (GLATOVS for SSU) | CRTM 2.1.3 for all radiances |
| Aerosols | Prescribed annual climatology (no assimilation) | Assimilates 550 nm aerosol optical depth from AVHRR, MODIS, MISR and AERONET; five GOCART aerosol species coupled to the model |
| Mass and water budgets | Large analysis increments, offset by unphysical variations in precipitation minus evaporation | Dry-air mass conserved (fixed at 983.24 hPa); global mean water vapour analysis increment constrained to zero |
| Land surface precipitation forcing | Model precipitation used as is | Corrected with observation-based precipitation for the land surface and wet deposition (provided as PRECTOTCORR; no correction poleward of 62.5°) |
| SST and sea-ice boundary conditions | Reynolds et al. (2002) 1° data | CMIP data before 1982, then NOAA OISST (1982–2006-03), then OSTIA (2006-04 onward) |
| Stratosphere, ozone and cryosphere | No QBO; SBUV v8 ozone (reduced to 12 layers) | Model generates a QBO; SBUV 8.6 (21 layers, to 2004) then OMI and MLS ozone from October 2004; MLS temperature assimilated above 5 hPa; glaciated land representation and seasonally varying sea-ice albedo |
| File format and collection names | HDF (.hdf), e.g. MAT1NXSLV V5.2.0 (no dataset DOI) | netCDF4 (.nc4), e.g. M2T1NXSLV V5.12.4 (a DOI for each collection) |
Things to watch when switching
- Do not splice the two reanalyses into one time series at 2016. Observations, model and boundary conditions all differ, so climatologies and trends differ even in the overlap period.
- Variable names (
T2M,SLP,PRECTOT, etc.) are largely the same, but collection names (MAT… to M2T…), file format (HDF to netCDF4) and grid (540 to 576 longitudes) changed, so reading and regridding scripts need updating. - MERRA-2 starts in 1980, so 1979 exists only in MERRA. For analyses that include 1979, compare with another reanalysis or adjust the period.
- Precipitation is now split into model (
PRECTOT) and observation-corrected (PRECTOTCORR) fields. When comparing with MERRA results, compare model precipitation with model precipitation.
Sources: Gelaro et al. (2017), The MERRA-2 reanalysis, J. Climate, 30, 5419–5454 · Rienecker et al. (2011), MERRA, J. Climate, 24, 3624–3648 · GMAO news — GMAO Terminates MERRA Production (2016-03-14) · GMAO MERRA official page · MERRA-2 File Specification (GMAO Office Note No. 9)
Available variables¶
Main variables from the MERRA file specification (GMAO Office Note No. 1). Short names are the in-file names; the collection is given in each group heading.
Time-stamp convention — instantaneous, mean or accumulated? — click to show
MERRA follows the same conventions as MERRA-2: inst collections hold instantaneous values at the time stamp, tavg collections hold interval averages time-stamped at the centre of the interval (00:30, 01:30, …). inst1_2d_int_Nx, which contains total precipitable water (TQV), is instantaneous on the hour, so it is offset by 30 minutes from tavg1 data even though both are hourly.
- tavg1_2d_slv_Nx and tavg1_2d_flx_Nx: hourly averages stamped at 00:30, 01:30, … (mid-interval)
- inst1_2d_int_Nx: vertically integrated quantities, instantaneous on the hour (00:00, 01:00, …)
- inst3_3d_asm_Cp: instantaneous at 00, 03, 06, …, 21 UTC (1.25° grid)
- Precipitation and heat fluxes are mean rates in kg m-2 s-1 and W m-2, not accumulations. Monthly files represent averages for the calendar months, accounting for leap years
instantaneous mean accumulated maximum minimum static — instantaneous: value at the time stamp · mean/accumulated/maximum/minimum: over the indicated interval · static: does not change with time
Surface and single level (tavg1_2d_slv_Nx, hourly average)¶
| Variable | Short name | Units | Time convention | Notes |
|---|---|---|---|---|
| Temperature at 2 m above the displacement height | T2M |
K | 1-hour mean | |
| Specific humidity at 2 m above the displacement height | QV2M |
kg kg-1 | 1-hour mean | |
| Eastward and northward wind at 10 m above the displacement height | U10M, V10M |
m s-1 | 1-hour mean | |
| Sea level pressure | SLP |
Pa | 1-hour mean | |
| Surface pressure | PS |
Pa | 1-hour mean |
Surface fluxes (tavg1_2d_flx_Nx, hourly average)¶
| Variable | Short name | Units | Time convention | Notes |
|---|---|---|---|---|
| Total surface precipitation flux | PRECTOT |
kg m-2 s-1 | 1-hour mean | |
| Sensible heat flux (positive upward) | HFLUX |
W m-2 | 1-hour mean | |
| Latent heat flux (positive upward) | EFLUX |
W m-2 | 1-hour mean |
Vertically integrated (inst1_2d_int_Nx, hourly instantaneous)¶
| Variable | Short name | Units | Time convention | Notes |
|---|---|---|---|---|
| Total water vapor (total precipitable water) | TQV |
kg m-2 | instantaneous |
Pressure levels (inst3_3d_asm_Cp, 3-hourly instantaneous, 1.25° grid, 42 levels)¶
| Variable | Short name | Units | Time convention | Notes |
|---|---|---|---|---|
| Air temperature | T |
K | instantaneous | |
| Eastward and northward wind components | U, V |
m s-1 | instantaneous | |
| Geopotential height | H |
m | instantaneous | |
| Specific humidity | QV |
kg kg-1 | instantaneous | |
| Relative humidity | RH |
fraction | instantaneous | |
| Vertical pressure velocity | OMEGA |
Pa s-1 | instantaneous |
The full variable list is in the official documentation.
How to get the data¶
- NASA GES DISC — MERRA dataset list — Web search and download
- Requires a NASA Earthdata Login. This is the official route given on the GMAO data access page.
- GES DISC on-premises archive (goldsmr1, MERRA directory) — HTTPS directory download
- Files for 1979–2016 are in per-collection folders such as MAT1NXSLV.5.2.0. The server banner says access ends after September 30, 2026, so it could close at any time. Requires an Earthdata Login.
- GMAO MERRA data access page — Information page
Practical tips¶
- MERRA was computed in three production streams, and the MERRA100/200/300 prefix in file names gives the stream number (e.g. MERRA100.prod.assim.tavg1_2d_slv_Nx.19790101.hdf). The prefix changes with the period, so read file names from the directory listing rather than hard-coding a fixed pattern.
- Values on pressure levels below the surface (e.g. 1000 or 850 hPa over high terrain) are undefined. Check how missing values are handled when averaging over regions that include mountains.
SPEEDin the FLX collection is the wind speed used in the turbulent flux calculation, not the ordinary surface wind. The GMAO FAQ advises using the 2 m winds (U2M,V2M) if you need surface wind.- Aerosols were not assimilated; an annual climatology was prescribed. For aerosol or radiation studies, use MERRA-2.
Notices and change history¶
2026-05-11 · Critical · GES DISC on-premises servers closing — access route for original MERRA uncertain
GES DISC announced that HTTPS access to data on its on-premises servers will no longer be available by September 30, 2026, as it moves to Earthdata Cloud. The goldsmr1 server holding the original MERRA carries the same closure notice, but whether the MERRA collections will be offered in the cloud has not been officially confirmed.
2016-03-14 · Critical · GMAO Terminates MERRA Production
On March 14, 2016, the MERRA production stream completed the analyses for February 29, 2016, the last date for which MERRA data will be produced. GMAO's reanalysis work has since moved to MERRA-2.
References for your paper¶
Double-check before using in a paper
The citations below were compiled by the maintainer and may contain errors. Always double-check DOIs, authors, years and access-date formats against the provider's official dataset page and your journal's guidelines.
Reference papers¶
MERRA reference paper — DOI 10.1175/JCLI-D-11-00015.1
Rienecker, M. M., Suarez, M. J., Gelaro, R., Todling, R., Bacmeister, J., Liu, E., Bosilovich, M. G., Schubert, S. D., Takacs, L., Kim, G.-K., et al. (2011): MERRA: NASA's Modern-Era Retrospective Analysis for Research and Applications. Journal of Climate, 24(14), 3624–3648.
Show BibTeX
@article{rienecker2011merra,
author = {Rienecker, Michele M. and Suarez, Max J. and Gelaro, Ronald and Todling, Ricardo and Bacmeister, Julio and Liu, Emily and Bosilovich, Michael G. and Schubert, Siegfried D. and Takacs, Lawrence and Kim, Gi-Kong and others},
title = {{MERRA}: {NASA}'s Modern-Era Retrospective Analysis for Research and Applications},
journal = {Journal of Climate},
volume = {24},
number = {14},
pages = {3624--3648},
year = {2011},
doi = {10.1175/JCLI-D-11-00015.1}
}
Acknowledgements¶
The MERRA README asks users to acknowledge GMAO and the data distributor, GES DISC. The original MERRA collections have no verifiable dataset DOI, so the safest approach is to cite the paper above together with the collection name you used (e.g. MAT1NXSLV V5.2.0) and your access date.
If this page helped, please acknowledge the Korean Climate Data Navigator
Please add the sentence below to the Acknowledgements of your paper.