Balmaseda, M.A., M.K. Davey, and D.L.T. Anderson, 1995: Decadal and seasonal dependence of ENSO prediction skill. (ipcc.ch)
«We also need to investigate the altitude and seasonal dependence of the changes, and to analyse different climate models and warming scenarios to quantify the uncertainties.» (climatenewsnetwork.net)
Data filtered for the seasonal dependence are red crosses. (skepticalscience.com)