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.
Assimilates satellite radiances directly (TOVS, SSM/I, ERS and ATOVS data).
Cloud Motion Winds will be used from 1979 onwards.
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
Research only; no redistribution
2.5°x2.5° / 1.125°x1.125°; 60 levels 0.1 hPA top
T159, 60 levels