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Probability density distributions of quasi-stationary waves (|c| < 2 m/s) at 500 mb for days in July−August during 1979–1999 (black) and 2000–2012 (red) for (A) wave 6, (B) wave 7, and (C) wave 8 in the Era Interim reanalysis. The shift in the distribution of wave 7 to higher amplitudes is statistically significant (see SI Appendix, Table S1).
