Empirical cotidal charts of N2, K2, P1 and Q1 in the Bohai, Yellow and East China Seas

The relative admittances of S2 versus M2, N2 versus M2, K2 versus S2, O1 versus K1, P1 versus K1 and Q1 versus O1 in the Bohai, Yellow and East China Seas are interpolated from harmonics at 113 long-term coastal and island tidal gauge stations. The empirical cotidal charts of N2, K2, P1 and Q1 are derived from the obtained relative admittance distribution and the cotidal charts of M2, S2, K1 and O1 obtained from satellite altimetry. Comparison with observed harmonics at 5 long-term tidal stations shows that the amplitude differences of these 4 constituents range from 0.3 to 1.9 cm, and the phase-lag differences range from 4 to 7°, except that the phase-lag differences become larger in the regions close to amphidromic points.