The term "re-analysis" is derived from the numerical analysis that is used in weather forecasts. The re-analysis data are calculated with models (similar to the ones used for weather prediction), that assimilate quality-assured monitoring data. The data contain global fields in different height levels of various parameters and are calculated over a long time period using all the appropriate observations. The aim of the re-analysis is to get a homogeneous data set, with high temporal and spatial resolution, that is suitable for the calculation of climatologies, for example.

The most important re-analysis products are:

American reanalyses of National Center for Environmental Prediction (NCEP):

• NCEP/NCAR Reanalysis
• NCEP/DOE AMIP-II Reanalysis
• NCEP NARR - North American Regional Reanalysis
• NCEP CFSR - Climate Forecast System Reanalysis

European re-analysis of  European Centre for Medium-Range Weather Forecast  (ECMWF):

• ERA40
• ERA Interim

Japanese 25-year re-analyses:

• JRA-25

NASA Goddard Space Flight Center re-analysis:

• NASA MERRA

A comprehensive collection of several reanalyses can be found on http://reanalyses.org/.

In the context of weather forecasting, the data produced for 0 o'clock are typically referred to as analysis. They are quickly available, but the quality is not as well as for the re-analyses.

• American predictions and analyses of GFS
• European predictions and analyses of ECMWF