Aneesh C Subramanian, University of Colorado Boulder, Atmospheric and Oceanic Sciences, Boulder, United States, Frederic Vitart, ECMWF, Reading, UK, United Kingdom, Magdalena Alonso Balmaseda, European Centre for Medium-Range Weather Forecasts, Reading, United Kingdom, Yosuke Fujii, Meteorological Research Inst, Tsukuba, Japan, Yuhei Takaya, Meteorological Research Institute, Climate Research Department, Ibaraki, Japan and Arthur J Miller, University of California San Diego, La Jolla, CA, United States