In this Letter, owing to an error during the production process, the colour bars to the left of the heat maps in Figs. 1f, 2d and 3c were inadvertently displayed entirely in red, instead of showing the full colour range of the corresponding heat maps. In addition, in the heat map in Fig. 2d, clusters 3 and 4 on the right below the ‘Asymmetric’ heading were inadvertently displayed entirely in red, instead of showing the full colour range of the time series. These figures have been corrected online.