Co-range Line

A co-range line is a line on a tidal chart joining points that have the same tidal range for a given constituent, the spatial complement of the co-tidal line, which marks equal phase. Around an amphidromic point the co-range lines form roughly concentric loops, with range zero at the point and increasing toward the basin margins where the reflected tide wave constructively reinforces. For the M2 constituent the co-range pattern explains extremes such as the large ranges of the Bay of Fundy and the near-zero ranges at central-basin nodes. Co-range and co-tidal charts together specify the amplitude and timing fields that tide-prediction models reconstruct.