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)