Fig. 2. a) Mean winter (DJF) Arctic Oscillation index, 1951-2004, b) mean winter (DJFM) East Pacific index, 1951-2004, c) Mean spring-summer (AMJJ) East Pacific index, 1950-2004, and d) mean spring-summer (AMJJ) North Pacific index from the Climate Prediction Center, 1950-2003. 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 0.1 for the NPICPC index and 0.05 for other indices