The results indicate that the exponential model performs well at both high and low frequency variability, which is consistent with inter-annual to inter-decadal climate-variability. In fact, the residuals between predicted and observed time-series are coherent in the validation period: residual histograms and Q-Q plots do not identify substantive departures from normality in both official run (Fig. \ref{div-295143}a, a1) and ensemble mean (Fig. \ref{div-295143}b, b1).
The data are somewhat right-skewed; however, the right tail of the distribution is fairly closely approximated by the normal distribution, with some high extreme values.