ERA-Interim is a global atmospheric reanalysis from 1979, continuously updated in real time.
The data assimilation system used to produce ERA-Interim is based on a 2006 release of the IFS (Cy31r2). The system includes a 4-dimensional variational analysis (4D-Var) with a 12-hour analysis window. The spatial resolution of the data set is approximately 80 km (T255 spectral) on 60 vertical levels from the surface up to 0.1 hPa.
ERA-Interim products are normally updated once per month, with a delay of two months (see Why can't I download ERA-Interim data for recent months) to allow for quality assurance and for correcting technical problems with the production, if any.
An open-access journal article describing the ERA-Interim reanalysis is available from the Quarterly Journal of the Royal Meteorological Society. Additional details of the modelling and data assimilation system used to produce ERA-Interim can be found in the IFS documentation Cy31r1. We are aware of several quality issues with ERA-Interim data.