The data assimilation system and initial performance evaluation of the ECMWF pilot reanalysis of the 20th-century assimilating surface observations only (ERA-20C)
Paul Poli, Hans Hersbach, David Tan, Dick Dee, Jean-Noel Thepaut, Adrian Simmons, Carole Peubey, Patrick Laloyaux, Takuya Komori, Paul Berrisford, Rossana Dragani, Yannick Tremolet, Elias Holm, Massimo Bonavita, Lars Isaksen, and Mike Fisher