
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