MERRA-2

 A subset of the MERRA-2 (Modern-Era Retrospective analysis for Research and Applications version 2 ) reanalysis is available on ClimServ.

MERRA-2 is a NASA atmospheric reanalysis for the satellite era using the Goddard Earth Observing System Model, Version 5 (GEOS-5) with its Atmospheric Data Assimilation System (ADAS), version 5.12.4. The MERRA project focuses on historical climate analyses for a broad range of weather and climate time scales and places the NASA EOS suite of observations in a climate context.

MERRA-2 was initiated as an intermediate project between the aging MERRA data and the next generation of Earth system analysis envisioned for the future coupled reanalysis. Without a substantial investment to update MERRA's data assimilation routines, the system lacked the capability to analyze the latest observations. In addition, numerous advances to the GEOS5 system had been implemented since freezing the MERRA system in 2008. Therefore, a new full reanalysis integration was undertaken. MERRA-2 covers the period 1980-present, continuing as an ongoing climate analysis as resources allow.

MERRA-2 output data resemble output at frequencies higher than the 6-hourly analyses. Two-dimensional diagnostics (surface fluxes, radiation, single level meteorology for those archived at IPSL) are produced at 1-hour intervals. These data products and the 3-hourly three-dimensional atmospheric analyses are also available at the full spatial resolution (1/2 degrees latitude × 2/3 degrees longitude).

The original files extracted at NASA GES DISC are in netcdf-4 format on ClimServ.

Four MERRA-2 datasets are available on ClimServ:

-M2I3NVASM (inst3_3d_asm_Nv): 3d,3-Hourly,Instantaneous,Model-Level,Assimilation,Assimilated Meteorological Fields (Thanks to B. Legras -LMD for his help for the 3d data access)

-M2T1NXFLX (tavg1_2d_flx_Nx): MERRA IAU 2D diagnostics, surface fluxes, time averaged, single level, at native resolution

-M2T1NXRAD (tavg1_2d-rad_Nx) :MERRA IAU 2D diagnostics, radiation surface and TOA, time averaged, single level, at native resolution

-M2T1NXSLV (tavg1_2d_slv_Nx): MERRA IAU 2D diagnostics, single-level  meteorology, time averaged, single level, at native resolution

 

Spatial coverage

Global area

native horizontal resolution:  1/2 degrees latitude × 2/3 degrees longitude  (longitude: 540, latitude : 361)

Temporal resolution

  •     8 times daily  for 3D parameters: 0, 3, 6, 9,12, 18, 24h GMT
  •    24 times daily for 2D parameters: 0:30, 1:30, 2:30, ......GMT

Temporal coverage

The MERRA-2period is: 1980-present; we will complete the dataset progessively on ClimServ. 

Levels

Model levels

The GEOS-5 model layers used for MERRA products are on a terrain-following hybrid sigma-p coordinate. Model-level data are output on the LM=72 layers; 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.

 

 

Available parameters

surface constant parameters (2D parameters):

PHIS - surface geopotential height (m2/s2)
SGH - standard deviation of topography for gravity wave drag (m)
FRLAKE - fraction of lake type in grid box (fraction)
FRLAND - fraction of land type in grid box (fraction)
FRLANDICE - fraction of land ice type in grid box (fraction)
FROCEAN - fraction of ocean in grid box (fraction)
AREA - horizontal area of grid box (m2)

surface (2D parameters)

 The parameters in blue are those extracted  the original M2T1NXFLX dataset full list below:

Variable Name

Description

Units

EFLUX Latent heat flux (positive upward) W m-2
EVAP Surface evaporation kg m-2s-1
HFLUX Sensible heat flux (positive upward) W m-2
TAUX Eastward surface wind stress N m-2
TAUY Northward surface wind stress N m-2
TAUGWX Eastward gravity wave surface stress N m-2
TAUGWY Northward gravity wave surface stress N m-2
PBLH Planetary boundary layer height m
DISPH Displacement height m
BSTAR Surface buoyancy scale m s-1
USTAR Surface velocity scale m s-1
TSTAR Surface temperature scale K
QSTAR Surface humidity scale kg kg-1
RI Surface Richardson number nondimensional
Z0H Roughness length, sensible heat m
Z0M Roughness length, momentum m
HLML Height of center of lowest model layer m
TLML Temperature of lowest model layer K
QLML Specific humidity of lowest model layer kg kg-1
ULML Eastward wind of lowest model layer m s-1
VLML Northward wind of lowest model layer m s-1
RHOA Surface air density kg m-3
CDH Surface exchange coefficient for heat kg m-2s-1
CDQ Surface exchange coefficient for moisture kg m-2s-1
CDM Surface exchange coefficient for momentum kg m-2s-1
CN Surface neutral drag coefficient nondimensional
TSH Effective turbulence skin temperature K
QSH Effective turbulence skin humidity kg kg-1
FRSEAICE Fraction of sea-ice fraction
PRECANV Surface precipitation flux from anvils kg m-2s-1
PRECCON Surface precipitation flux from convection kg m-2s-1
PRECLSC Surface precipitation flux from large-scale kg m-2s-1
PRECSNO  Surface snowfall flux kg m-2s-1
PRECTOT Total surface precipitation flux kg m-2s-1
PGENTOT Total generation of precipitation kg m-2s-1
PREVTOT Total re-evaporation of precipitation kg m-2s-1

  The parameters in blue are those extracted  from the original M2T1NXRAD dataset full list below:

Variable Name

Description

Units

EMIS Surface emissivity fraction
TS Surface skin temperature K
ALBEDO Surface albedo fraction
ALBNIRDF Diffuse beam NIR surface albedo fraction
ALBNIRDR Direct beam NIR surface albedo fraction
ALBVISDF Diffuse beam VIS-UV surface albedo fraction
ALBVISDR Direct beam VIS-UV surface albedo fraction
LWGEM Emitted longwave at the surface W m-2
LWGAB Absorbed longwave at the surface W m-2
LWGABCLR Absorbed longwave at the surface with no clouds W m-2
LWGABCLRCLN Absorbed longwave at the surface with no clouds or aerosol W m-2
LWGNT Net downward longwave flux at the surface W m-2
LWGNTCLR Net downward longwave flux at the surface for cloud-free sky W m-2
LWGNTCLRCLN Net downward longwave flux at the surface for clear sky W m-2
LWTUP Upward longwave flux at top of atmosphere (TOA) W m-2
LWTUPCLR Upward longwave flux at TOA assuming clear sky W m-2
LWTUPCLRCLN Upward longwave flux at TOA assuming clear clean sky W m-2
SWTDN TOA incident shortwave flux W m-2
SWGDN Surface incident shortwave flux W m-2
SWGDNCLR Surface incident shortwave flux assuming clear sky W m-2
SWGNT Surface net downward shortwave flux W m-2
SWGNTCLR Surface net downward shortwave flux assuming clear sky W m-2
SWGNTCLN Surface net downward shortwave flux assuming clean sky W m-2
SWGNTCLRCLN Surface net downward shortwave flux assuming clear clean sky W m-2
SWTNT TOA net downward shortwave flux W m-2
SWTNTCLR TOA net downward shortwave flux assuming clear sky W m-2
SWTNTCLN TOA net downward shortwave flux assuming clean sky W m-2
SWTNTCLRCLN TOA net downward shortwave flux assuming clear clean sky W m-2
TAUHGH Optical thickness of high clouds dimensionless
TAULOW Optical thickness of low clouds dimensionless
TAUMID Optical thickness of mid-level clouds dimensionless
TAUTOT Optical thickness of all clouds dimensionless
CLDHGH High-level (above 400 hPa) cloud fraction fraction
CLDLOW Low-level (1000-700 hPa) cloud fraction fraction
CLDMID Mid-level (700-400 hPa) cloud fraction fraction
CLDTOT Total cloud fraction fraction

 

The parameters in blue are those extracted from the original M2T1NXSLV dataset full list below: 

Variable Name

Description

Units

SLP Sea level pressure Pa
PS Time averaged surface pressure Pa
U850 Eastward wind at 850 hPa m s-1
U500 Eastward wind at 500 hPa m s-1
U250 Eastward wind at 250 hPa m s-1
V850 Northward wind at 850 hPa m s-1
V500 Northward wind at 500 hPa m s-1
V250 Northward wind at 250 hPa m s-1
T850 Temperature at 850 hPa K
T500 Temperature at 500 hPa K
T250 Temperature at 250 hPa K
Q850 Specific humidity at 850 hPa kg kg-1
Q500 Specific humidity at 500 hPa kg kg-1
Q250 Specific humidity at 250 hPa kg kg-1
H850 Height at 850 hPa m
H500 Height at 500 hPa m
H250 Height at 250 hPa m
OMEGA500 Vertical pressure velocity at 500 hPa Pa s-1
U10M Eastward wind at 10 m above displacement height m s-1
U2M Eastward wind at 2 m above the displacement height m s-1
U50M Eastward wind at 50 m above surface m s-1
V10M Northward wind at 10 m above the displacement height m s-1
V2M Northward wind at 2 m above the displacement height m s-1
V50M Northward wind at 50 m above surface m s-1
T10M Temperature at 10 m above the displacement height K
T2M Temperature at 2 m above the displacement height K
QV10M Specific humidity at 10 m above the displacement height kg kg-1
QV2M Specific humidity at 2 m above the displacement height kg kg-1
TS Surface skin temperature K
DISPH Displacement height m
TROPPV PV based tropopause pressure Pa
TROPPT T based tropopause pressure Pa
TROPPB blended tropopause pressure Pa
TROPT Tropopause temperature K
TROPQ Tropopause specific humidity kg kg-1
CLDPRS Cloud-top pressure Pa
CLDTMP Cloud-top temperature K

 

Model level (3D parameters)

  The parameters in blue are those extracted  from the original M2I3NVASM dataset full list: 

Variable Name

Dims

Description

Units

PS 2D Surface pressure Pa
OMEGA
3D Vertical pressure velocity
Pa s-1
T 3D Air temperature K
U 3D Eastward wind component m s-1
V 3D Northward wind component m s-1
QV 3D Specific humidity kg kg-1
QI 3D mass fraction of cloud ice water kg kg-1
QL 3D mass fraction of cloud liquid water kg kg-1

 

Access

The access to this dataset is restricted to the members of IPSL. 

You can access data by several ways :

  • from your login on climserv server: cd /bdd/MERRA-2/. 
    To have an access on our server, please mail to  Cet e-mail est protégé contre les robots collecteurs de mails, votre navigateur doit accepter le Javascript pour le voir
  • by ftp : ftp://ftp.climserv.ipsl.polytechnique.fr/MERRA-2/

 

Format

The data files are in the netCDF-4 format, classical model  and are compatible with the CF convention. It defines the meaning of attributes, the units, the coordinate variables.

The files are organized by variable, by day. 

Related file Naming and Structure information

The MERRA data are stored on the directory: /bdd/MERRA-2/
  • The subdirectories are the following:/FFF/RESOL/XXX/LL/YYYY/MM/name_file
  • FFF: format (NC)
  • RESOL: is the resolution:  native_resol
  • XXX: is the temporal resolution (daily)
  • LL: LL is the level type (SF for surface, ML for Model Level)
  • YYYY: year
  • MM: month 
  • File names: NAME.MERRAID.YYYYMMDD.nc4
  • NAME: is the netcdf parameter name (see parameters lists)
  • MERRAID: MERRA-2 dataset name ID
  • YYYYMMDD: date 

 

Original source

http://gmao.gsfc.nasa.gov/research/MERRA-2/ 

Original access

http://mirador.gsfc.nasa.gov/cgi-bin/mirador/presentNavigation.pl?tree=project&project=MERRA -2&CGISESSID=9409d1d84b6ab9b6a309b013fa6575c1

http://goldsmr4.sci.gsfc.nasa.gov/opendap/MERRA2/

http://disc.sci.gsfc.nasa.gov/uui/search/%22MERRA-2%22

Documents:

http://gmao.gsfc.nasa.gov/reanalysis/MERRA-2/docs/

File specification: http://gmao.gsfc.nasa.gov/pubs/docs/Bosilovich785.pdf

MERRA pages on the Climate data guide web site (from NCAR): https://climatedataguide.ucar.edu/reanalysis/nasa-merra 

Web site for reanalysis  intercomparisons: http://www.reanalyses.org

Acknowledgements

To cite the data in publications:
Global Modeling and Assimilation Office (GMAO) (2015),MERRA-2 inst1_2d_asm_Nx: 2d,3-Hourly,Instantaneous,Single-Level,Assimilation,Single-Level Diagnostics,version 5.12.4, Greenbelt, MD, USA:Goddard Space Flight Center Distributed Active Archive Center (GSFC DAAC), Accessed Enter User Data Access Date at doi:10.5067/3Z173KIE2TPD 

Contact (IPSL)

Sophie Cloché-IPSL
Ecole Polytechnique
91128 Palaiseau cedex
FRANCE
Tel: 33 (1) 69 33 51 31
mailto: Cet e-mail est protégé contre les robots collecteurs de mails, votre navigateur doit accepter le Javascript pour le voir
Dernière mise à jour : ( 30-03-2017 )