Next, for nodes $i$ and $j$, and for each time point $t$, the maximum, them mean and the SD around the mean are determined for $|C_{i,j}^t|$, as $\tau$ varies across its range.

Define the _link strength_ $S_{i j}(t)$ as the difference between this maximum and mean value, divided by the SD.

They say:

> Accordingly, $S_{i j}(t)$ describes the link strength at day t relative to the underlying background and thus quantifies the dynamical teleconnections between nodes i and j.

Next, let the mean strength $S(t)$ of the dynamical teleconnections in the climate network be the average over all individual link strengths.