Quantile-quantile (“q-q”) plots to test the similarity of corresponding distributions for the southern and northern hemispheres: (a). for 3-hourly values of aa _N and aa _S; (b) for the daily means of aa _N and aa _S , Aa _N and Aa _S; (c) 3-hourly values of aa _HN and aa _HS and (d) their daily means Aa _HN and Aa _HS. The mauve points mark the 90%, 99%, 99.9% and 99.99% percentile points and the orange is for 99.97%. Also shown in blue in part (b) is the 99.7% percentile. Points would lie along the diagonal green line if the distributions from the two hemispheres had the same shape.