Climate Data


ERA 40 is a second generation reanalysis. It is the first reanalysis to directly assimilate satellite radiance data (TOVS, SSM/I, ERS and ATOVS). Cloud Motion Winds are also used. The result is better circulation over the tropics and southern hemisphere. However, unless comparing  to previous ERA-40 based results, it is recommended that the 3rd generation reanalyses, ERA-Interim or MERRA, be used for new research.

Key Strengths:

  • Assimilates satellite radiances directly (TOVS, SSM/I, ERS and ATOVS data).
  • Cloud Motion Winds will be used from 1979 onwards.

Key Limitations:

  • Tropical moisture (precipitation, total column water vapor) larger than observed from 1991 onward
  • Precipitation greatly exceeds evaporation
  • Brewer Dobson circulation is too intense; Spurious Arctic temperature trends

Years of Record

1957/09 to 2002/08
temporal metadataID:



Sub-daily | Monthly

Data Time Period Extended?

no, data set not being extended


Spatial Resolution

2.5°x2.5° / 1.125°x1.125°; 60 levels 0.1 hPA top

Ocean or Land


Missing Data Flag

spatially complete

Data Assimilation Method

Model Resolution used to create reanlaysis

T159, 60 levels

Model Vintage (reanalysis)


Earth system components and main variables

Usage Restrictions

Research only; no redistribution

Key Figures

Click the thumbnails to view larger sizes



ERA40: January monthly mean potential vorticity at 300hPa.

Cite this page

National Center for Atmospheric Research Staff (Eds). Last modified 01 Mar 2016. "The Climate Data Guide: ERA40." Retrieved from

Acknowledgement of any material taken from this page is appreciated. On behalf of experts who have contributed data, advice, and/or figures, please cite their work as well.