The map for D1 of increases (or decreases) of the number of anomalies as a function of the middle day of the first and second 3-day periods, together with maps of the corresponding p-values. The upper row is computed for IntDst as the reference series, whereas the lower row is for Int(d(SYM-H) = dt) series. The p-values in the right column are evaluated only if there is an increase of the grid anomaly rates in the second 3-day period as compared to the first 3-day period. Note the logarithmic scale of the plotted p-values: p = 0.0055 (the adopted level of statistical significance for individual bins) corresponds to log p = − 2.26. Statistically significant bins are indicated by white dots. Blank bins are indicated by the white colour.