Fig. 1. a) Mean winter (DJF) PDO index, 1901-2004, b) mean summer (JJA) PDO index, 1900-2004, c) Annual (Jan-Dec) PDO index, 1900-2003, and d) North Pacific index (Nov-Mar) from the National Center for Atmospheric Research (Trenberth and Hurrell 1994), 1900-2004. The stepwise functions (orange lines) characterize regime shifts in the level of fluctuations of the indices. Shift points were calculated using the STARS method (Rodionov 2004), with the cutoff length of 10 years and significance levels of 0.05 for the PDO indices and 0.2 for the NPI_NCAR index.