MERRA

NASA/GMAO ceased production of MERRA data as of June 2013 (as it was produced with the same assimilation system as the GEOS-5.2.0 data). Therefore, you will not be able to use MERRA met fields to run GEOS-Chem global simulations for model dates after June 2013. But you can still run GEOS-Chem simulations using our archive of MERRA meteorology, which spans the years 1979 through 2010.
The current GMAO met data product is now the GEOS-FP operational product, which is supported in GEOS-Chem v9-02 and higher versions. We are processing GEOS-FP data for 2012 up to present day. You will be able to use GEOS-FP for both global and hi-res (0.25° x 0.3125°) nested-grid simulations starting with GEOS-Chem v9-02.
GMAO has plans to create a new reanalysis (MERRA-2) using the current GEOS-DAS version (v5.11.0). MERRA-2 will look very similar to the current GEOS-FP operational data product.
— Bob Yantosca, 28 May 2014

This page describes some basic information about the GMAO MERRA data product.

Overview

The GMAO MERRA data product is a 30-year reanalysis done with the GEOS-5.2.0 assimilation system. This was done to supplement the GEOS-5 operational data product, which only has data from 2004-present.

Please visit the links below to learn more about the MERRA data:

Also be sure to see our Overview of GMAO met data products page for some basic information about the different generations of GMAO met data used by GEOS-Chem.

--Bob Y. 14:34, 19 October 2011 (EDT)

Acknowledge the source of MERRA data in your publications

If your GEOS-Chem research depends on the MERRA meteorological data product, then please consider adding an acknowledgment to your publications such as:

MERRA data used in this study/project have been have been provided by the Global Modeling and Assimilation Office (GMAO) at NASA Goddard Space Flight Center through the NASA GES DISC online archive.

--Bob Y. 14:35, 23 April 2012 (EDT)

List of GEOS-Chem projects using MERRA data

On this page we list people who are using GEOS-Chem driven by the GMAO MERRA reanalysis product. Please feel free to add your own project to this list!

Investigator(s)	Institution	Project
Helen Amos	Harvard	Mercury simulation
Helen Amos	Harvard	Investigating MERRA vs. GEOS-5 differences in wet deposition
Tom Breider	Harvard	Investigating aerosols & ozone over the arctic
Jenny Fisher	Harvard	Running 30-year MERRA mercury simulations with focus on the Arctic
David Ridley	MIT	Running 30-year MERRA simulations focusing on dust.
Lei Zhu	Harvard	Temperature and soil moisture dependence for HCHO emission.
Amos Tai, Yu Fu	CUHK	Impact of historical climate and land cover changes on East Asian air quality.

--Bob Y. 14:47, 19 October 2011 (EDT)

MERRA data availability

The following plot shows the MERRA data availability. To facilitate throughput, GSFC created the MERRA data in 3 separate streams: MERRA100 (1979-1993), MERRA200 (1993-2001), and MERRA300 (2001-2011+).

This plot was created in 2010, so it does not show any data past that point. MERRA300 extends out to 2011-2012. GMAO will turn off further MERRA processing very shortly, so there will not be much data past late 2011/early 2012.

--Bob Y. 10:25, 23 July 2012 (EDT)

MERRA grid structure

This section describes the horizontal and vertical grids used by the MERRA data products.

Input grids

From the MERRA File Specification Document, page 2:

The analysis is performed at a horizontal resolution of 2/3 degrees longitude by 1/2 degree latitude and at 72 levels, extending to 0.01 hPa. Some products, such as the instantaneous analysis fields, are available on the native three-dimensional grid. Hourly two-dimensional diagnostic fields are also available at the native horizontal resolution. Other products are available on a coarser horizontal grid with resolution of 1.25 ×1.25 degrees or 1 × 1.25 degrees, the latter for use by the chemistry transport community. These may be on the model’s native vertical grid or at 42 pressure surfaces extending to 0.1 hPa. Surface data, near surface meteorology, selected upper air levels, and vertically integrated fluxes and budgets are produced at one-hour intervals, which will help the development of offline land and ocean models and data assimilation systems by resolving the diurnal cycle.

and on page 9:

Gridded products will use four different vertical configurations: Horizontal-only (can be vertical averages, single level, or surface values), pressure-level, model-level, or model-edge. Horizontal only data for a given variable appear as 3-dimensional fields (x, y, time), where multiple times can span multiple files, while pressure-level, model-level, or model-edge data appear as 4-dimensional fields (x, y, z, time). Pressure-level data will be output on the LMp=42 pressure levels. The GEOS-5 model layers used for MERRA output are on a terrain-following hybrid sigma-p coordinate. Model-level data will be output on the LM=72 layers. The model-edge products contain fields with LMe = LM + 1 levels representing the layer edges....

Note that the indexing for the GEOS-5 vertical coordinate system in the vertical is top to bottom, i.e., layer 1 is the top layer of the atmosphere, while layer LM is adjacent to the earth’s surface. The same is true for edge variables, with level 1 being the top of the model’s atmosphere (PTOP), and level LM+1 being the surface.

The table below lists the combination of the horizontal and vertical grids onto which the MERRA "raw" data products are placed:

Grid	Name	Horizontal Resolution	Vertical Resolution	Used for	Notes
Native, single layer	Nx	0.5° x 0.666°	1 level	Surface data fields (e.g. PS, EVAP, HFLUX, etc.)	Identical to GEOS-5 native horizontal grid
Native, vertical centers	Nv	0.5° x 0.666°	72 hybrid levels	Most 3D data fields (e.g. U, V, T, etc.)	Identical to GEOS-5 native horizontal grid + GEOS-5 native vertical grid
Native, vertical edges	Ne	0.5° x 0.666°	73 hybrid level edges	Data fields defined on level edges (e.g. PLE)	Identical to GEOS-5 native horizontal grid + GEOS-5 native vertical grid
Reduced FV, single layer	Fx	1° x 1.25°	1 level	Surface data fields (e.g. T2M, U10M, V10M, etc.)	Identical to GEOS-4 native horizontal grid
Reduced FV, vertical centers	Fv	1° x 1.25°	72 hybrid levels	Most 3D data fields (e.g. U, V, T etc.)	Identical to GEOS-4 native horizontal grid + GEOS-5 native vertical grid
Reduced FV, vertical edges	Fe	1° x 1.25°	73 hybrid level edges	Data fields defined on level edges (e.g. CMFMC)	Identical to GEOS-4 native horizontal grid + GEOS-5 native vertical grid
Pressure	Cp	1.25° x 1.25°	42 pressure levels: 1000, 970, 950, 925, 900, 875, 850, 825, 800, 775, 750, 725, 700, 650, 600, 550, 500, 450, 400, 350, 300, 250, 200, 150, 100, 70, 50, 40, 30, 20, 10, 7, 5, 4, 3, 2, 1 0.7, 0.5, 0.4, 0.3, 0.1 hPa	Various 3D data fields (e.g. DQIDTMST, etc.)	Cp is edged on (-180,-90) unlike the "N" and "F" grids which are centered on (-180,-90)

The longitudes and latitudes of the Native (Nx, Nv, Ne) grids are constructed as follows:

Lon_Edge(I)   = ( -180° - DI/2 ) + ( DI * I ),  I = 0, 540
Lat_Edge(J)   = ( -90°  - DJ/2 ) + ( DJ * J ),  J = 0, 361

Lon_Center(I) = -180° + ( DI * ( I - 1 ) ),     I = 1, 540
Lat_Center(J) =  -90° + ( DJ * ( J - 1 ) ),     J = 1, 361

where DI = 2/3° and DJ = 1/2°.

The longitudes and latitudes of the Reduced FV (Fx, Fv, Fe) grids are constructed as follows:

Lon_Edge(I)   = ( -180° - DI/2 ) + ( DI * I ),  I = 0, 288
Lat_Edge(J)   = ( -90°  - DJ/2 ) + ( DJ * J ),  J = 0, 181

Lon_Center(I) = -180° + ( DI * ( I - 1 ) ),     I = 1, 288
Lat_Center(J) =  -90° + ( DJ * ( J - 1 ) ),     J = 1, 181

where DI = 1.25° and DJ = 1°.

The longitudes and latitudes of the Pressure (Cp) grid are constructed as follows:

Lon_Edge(I)   = -180° + ( DI * I ),             I = 0, 288
Lat_Edge(J)   =  -90° + ( DJ * J ),             J = 0, 144

Lon_Center(I) = -180° + ( DI * ( I - 1/2° ) ),  I = 1, 288
Lat_Center(J) =  -90° + ( DJ * ( J - 1/2° ) ),  J = 1, 144

where DI = 1.25° and DJ = 1.25°.

--Bob Y. 10:19, 6 August 2010 (EDT)

Output grids

The grid structure of MERRA precludes the construction of the 0.5° x 0.667° nested grids, as for certain individual data fields the finest resolution available is 1.25° x 1.25°.

At present, we foresee the use of MERRA only at the following resolutions:

As of August 2010, Harvard will only regrid MERRA data to the 4° x 5° grid (due to both time and disk space constraints). The 2° x 2.5° data have been produced at Dalhousie, and are available on the Dalhousie archive.

Bob Yantosca will make the MERRA regridding code available to GEOS-Chem users who would like to process the MERRA data for their own applications.

--Bob Y. 10:19, 6 August 2010 (EDT)

Please note that there was a problem in the regridded MERRA data for December 19th 1983 (causing GEOS-Chem to crash). These have been reprocessed by Bob Y. on March 28th 2012. If you transferred the MERRA files prior to this date please make sure you re-download the A1, A3 and A6 files for December 19th 1983.

--David Ridley 02:56, 8 June 2012 (EDT)

MERRA file naming convention

The following description of the naming convention used for MERRA "raw" data files is paraphrased from Section 5.1 and 5.2 of the MERRA File Specification Document, pp 10ff:

Standard names

The standard full name for the assimilated GEOS-5 MERRA products will consist of five dot-delimited nodes:

       runid.runtype.config.collection.timestamp

The node fields, which vary from file to file, are defined as follows:

runid

For mainstream MERRA data, the following runid's are used:

MERRA100: Years from 1979-1993

MERRA200: Years from 1993-2001

MERRA300: Years from 2001-2010

runtype

The main GEOS-5 MERRA products will be from standard production runs (denoted by prod).

config

The GEOS-5 analysis and forecast system can run in different configurations. The mainline MERRA data product is assimilation data (denoted by assim). The assimilation uses a combination of atmospheric data analysis and model forecasting to generate a time-series of global atmospheric quantities.

collection

Collection names are of the form freq_dims_group_HV, where the four attributes are:

freq: time-independent (cnst), instantaneous (instF), or time-average (tavgF), where F indicates the frequency or averaging interval and can be any of the following:
1 = Hourly

3 = 3-Hourly

6 = 6-Hourly

0 = Not Applicable

dims: Can be either:
2d for collections with only 2-dimensional fields or

3d for collections with a mix of 2- and 3-dimensional fields.

group: A three-letter mnemonic for the type of fields in the collection.

HV: Horizontal and Vertical grid.
H can be:
N: Native (2/3° x 1/2°) horizontal resolution

C: Reduced (1.25° x 1.25°) horizontal resolution

F: Reduced FV (1.25° x 1°) horizontal resolution

V can be:
x: horizontal-only data (surface, single level, etc.) ; dims must be 2D

p: pressure-level data (see Appendix D for levels) ; dims must be 3D

v: model layer centers (see Appendix D ) dims must be 3D

e: model layer edges (see Appendix D ) dims must be 3D

timestamp

This node defines the date and time associated with the data in the file. It has the form yyyymmdd

yyyy - year string (e.g. , 2002)

mm - month string (e.g.., 09 for September)

dd - day of the month string

EXAMPLE:

       MERRA300.prod.assim.tavg3_3d_tdt_Cp.20020915.hdf

This is an example of a MERRA filename from the production segment of the original version of the third (most recent) assimilation stream. The data are time-averaged, three-dimensional, temperature tendency products, at reduced horizontal resolution, interpolated to pressure levels. The file contains all data for 15 September 2002.

ESDT names

To accommodate certain software requirements, all MERRA files are associated with a nine character ESDT. The ESDT is a short (and rather cryptic) handle for users to access sets of files. In MERRA the ESDT will be used to identify collections and will consist of a compressed version of the collection name of the form:

       MCTFHVGGG

where

C: Configuration
A = Assimilation

T: Time Description:
I = Instantaneous

T = Time-averaged

C = Time-independent

F: Frequency
1 = Hourly

3 = 3-Hourly

6 = 6-Hourly

0 = Not Applicable

H: Horizontal Resolution
N = Native.

F = Reduced resolution version of model grid

C = Reduced resolution

V: Vertical Location
X = Two-dimensional

P = Pressure

V = model layer center

E = model layer edge

GGG: Group
ANA = direct analysis products

ASM = assimilated state variables (from the IAU corrector, see Appendix A)

TDT = tendencies of temperature

UDT = tendencies of eastward and northward wind components

QDT = tendencies of specific humidity

ODT = tendencies of ozone

LND = land surface variables

FLX = surface turbulent fluxes and related quantities

MST = moist processes

CLD = clouds

RAD = radiation

TRB = turbulence

The ESDT name is also used in the various FTP file paths to the MERRA data directories at GSFC.

--Bob Y. 12:51, 4 August 2010 (EDT)

MERRA data file collections

In this section we list the MERRA "raw" data files that are used to create the data archive for GEOS-Chem. This is a subset of all of the available MERRA data. Information in the table is taken from Section 6 of the MERRA File Specification Document, page 15ff:

File collection name	ESDT Name (aka "short name")	Description	Times	Size (GB/day)
`const_2d_asm_Nx`	MAC0FXCHM	Constant fields	Time-invariant	0.0002
`tavg1_2d_flx_Nx`	MAT1NXFLX	Surface turbulent fluxes and related quantities	1-hr time averages	0.267
`tavg1_2d_lnd_Nx`	MAT1NXLND	Land related surface quantities	1-hr time averages	0.146
`tavg1_2d_rad_Nx`	MAT1NXRAD	Surface and TOA radiative fluxes	1-hr time averages	0.189
`tavg1_2d_slv_Nx`	MAT1NXSLV	Single-level atmospheric state variables	1-hr time averages	0.285
`tavg3_2d_chm_Fx`	MAT3FXCHM	Chemistry related 2-D Single-level	3-hr time averages	0.020
`tavg3_3d_chm_Fv`	MAT3FVCHM	Chemistry related 3-D at model layer centers	3-hr time averages	0.329
`tavg3_3d_chm_Fe`	MAT3FECHM	Chemistry related 3-D at model layer edges	3-hr time averages	0.166
`tavg3_3d_mst_Cp`	MAT3CPMST	Upper-air diagnostics from moist processes	3-hr time averages	0.056
`tavg3_3d_qdt_Cp`	MAT3CPQDT	Upper-air humidity tendencies by process	3-hr time averages	0.166
`inst3_3d_asm_Cp`	MAI3CPASM	Basic assimilated fields from IAU corrector	3-hr instantaneous	0.231
`inst6_3d_ana_Nv`	MAI6NVANA	Analyzed fields on model layers	6-hr instantaneous	0.452
TOTAL				2.307

As described in Section 3, the full file name for mainstream MERRA data products is of the form:

MERRAXXX.prod.assim.CCCCCCCCCCCCCCC.YYYYMMDD.hdf

where

XXX is the runid (e.g. "100", "200", or "300")
CCCCCCCCCCCCCCC is the collection name (i.e. one of the entries in the first column of the above table)
YYYYMMDD is the year/month/day date

--Bob Y. 12:56, 4 August 2010 (EDT)

MERRA time archiving

Raw data

The MERRA raw data are archived/averaged at the following times:

const: Time-invariant data
inst3: 3-hr instantaneous data
- Times: 00:00, 03:00, 06:00, 09:00, 12:00, 15:00, 18:00, 21:00 GMT
inst6: 6-hr instantaneous data
- Times: 00:00, 06:00, 12:00, 18:00 GMT
tavg1: 1-hour time-averaged data
- Center times: 00:30, 01:30, 02:30 ... 23:30 GMT
tavg3: 3-hour time-averaged data
- Center times: 01:30, 04:30, 07:30, 10:30, 13:30, 16:30, 19:30, 22:30 GMT

Regridded data

The regridded MERRA data for GEOS-Chem are archived at the following times:

CN (time-invariant data)
- Filenames 20000101.cn.2x25 and/or 20000101.cn.4x5
A1 (1-hr time-averaged data)
- Filenames YYYYMMDD.a1.2x25 and/or YYYYMMDD.a1.4x5
A3 (3-hr time-averaged data)
- Filenames YYYYMMDD.a3.2x25 and/or YYYYMMDD.a3.4x5
I6 (6-hr instantaneous data)
- Filenames YYYYMMDD.i6.2x25 and/or YYYYMMDD.i6.4x5

The CN files contain time-invariant data.

The I6 files contain instantaneous (i.e. snapshot) data at 00:00, 06:00, 12:00, 18:00 GMT.

The A1 and A3 files use the following bins for time-averaging:

Please also see our List of MERRA met fields wiki page for detailed information about which fields are stored in each of these file types.

--Bob Y. 16:09, 11 August 2010 (EDT)

Implementation into GEOS-Chem

Please see our MERRA implementation details wiki page for more information about the specifics of how GEOS-Chem is being modified to use the MERRA met product.

--Bob Y. 10:42, 16 August 2010 (EDT)

Working with MERRA data on your own

The MERRA Atlas

The MERRA ATLAS provides a global visual perspective into many of the variables that are output by the NASA atmospheric reanalysis for the satellite era (1979-present). MERRA uses the Goddard Earth Observing System Data Assimilation System Version 5.2.0 (GEOS-5.2.0) run at 1/2 degrees latitude by 2/3 degrees longitude and with 72 levels.

While the full MERRA output suite contains a large number of two and three-dimensional output fields, the MERRA atlas shall focusus initially on the monthly mean of a few selected single level or pressure level fields. More information about MERRA, including system documentation, the MERRA output and how to obtain the data, is available at http://gmao.gsfc.nasa.gov/research/merra/. It is anticipated the atlas will evolve to include more fields including sub-monthly transients and various time series.

Create plots from MERRA data online

For those of you who want to see monthly mean plots of MERRA data, you can do that online via the GIOVANNI utility at NASA. GIOVANNI is a Web-based application developed by the GES-DISC that provides a simple and intuitive way to visualize, analyze, and access vast amounts of Earth science remote sensing data without having to download the data.

Please see the following web links:

Subsetting MERRA data

You have the option of asking NASA's GES-DISC (i.e. the department that handles data download requests) for MERRA data files that have been subsetted, or "cut down to size". This may help you to avoid having to download and archive the large global MERRA data files.

Please see the MERRA data subset web interface for more information.

--Bob Y. 14:20, 15 December 2010 (EST)

Reading MERRA raw data files with IDL

You can read any of the MERRA data files directly into IDL. The GAMAP visualization package contains a routine callee EOS_GETGR that you can use to read the MERRA data in its native in HDF4-EOS format.

Step 1: Download the data file that you need. The MERRA data are available via a simple FTP file transfer. However, we recommend using the GNU wget utility, which will simplifly the download process. For example, to download a data file that contains the MERRA FRSEAICE data field, use this command:

wget –nd “ftp://goldsmr2.sci.gsfc.nasa.gov/data/s4pa/MERRA/MAT1NXFLX.5.2.0/2008/04/MERRA300.prod.assim.tavg1_2d_flx_Nx.20080412.hdf

Step 2: Once you have downloaded a MERRA data file, you can read it into IDL with this sequence (or include this into your own IDL program):

IDL> FID = EOS_GD_OPEN( 'MERRA300.prod.assim.tavg1_2d_flx_Nx.20080412.hdf', /READ )
     
IDL> DATA = EOS_GETGR( fId, 'FRSEAICE', GRIDNAME='EOSGRID' )

IDL> help, data, /stru
DATA            FLOAT     = Array[540, 361, 24]

IDL> STATUS = EOS_GD_CLOSE( FID )

etc.

For more information, please see:

MERRA data holdings web page. (This web page lists the file names and the FTP data paths.)
List of MERRA met fields

--Bob Y. 17:11, 7 March 2011 (EST)

MERRA

Contents

Overview

Acknowledge the source of MERRA data in your publications

List of GEOS-Chem projects using MERRA data

MERRA data availability

MERRA grid structure

Input grids

Output grids

MERRA file naming convention

Standard names

ESDT names

MERRA data file collections

MERRA time archiving

Raw data

Regridded data

Implementation into GEOS-Chem

Working with MERRA data on your own

The MERRA Atlas

Create plots from MERRA data online

Subsetting MERRA data

Reading MERRA raw data files with IDL

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