[ Derived from parent entry - See data hierarchy tab ] The reanalysis project of the ECMWF (ecmwf.int) ERA-40 covers the 45 years period from Sep 1957 to Aug 2002. So it includes the period of the earlier ERA-15 reanalysis. The main objective is to promote the use of global analyses of the state of the atmosphere, land and surface conditions. The datasets of this experiment contain the four monthly means of the 30 (28,29,31 respectively) daily values (at 00,06,12,18 UTC separately).