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.