There was a numerical error in the abstract of Mitchell et al. (2012). In the fourth sentence of the abstract the number should be 7 events per decade, not 0.7. The full sentence should read, “Analysis of the standard stratospheric zonal mean wind diagnostic shows no significant increase over the twenty-first century in the number of major sudden stratospheric warmings (SSWs) from its historical value of 7 events per decade, although the monthly distribution of SSWs does vary, with events becoming more evenly dispersed through the winter.”
The staff of the Journal of the Atmospheric Sciences regrets any inconvenience this error may have caused.
Mitchell, D. M., S. M. Osprey, L. J. Gray, N. Butchart, S. C. Hardiman, A. J. Charlton-Perez, and P. Watson, 2012: The effect of climate changes on the variability of the Northern Hemisphere stratospheric polar vortex. J. Atmos. Sci., 69, 2608–2618.