Large radiational S₂ tides in the East China Sea

S-2 ocean tide, as one of the most important semi-diurnal constituents, is composed of astronomical S-2 tide originated from gravitational forcing and radiational S-2 tide derived from solar radiation. Although there are lots of researches which have explored the features of radiational S-2 tides in the globe, less known and less discussed, are the radiational S-2 tides in the East China Sea due to lack of water level observations. In present study, radiational S-2 tides in the East China Sea are estimated and discussed via the combination of 39 coastal tide gauges and EOT20 tidal model derived from multi-satellite altimeter records. We find that radiational S-2 tides obtained from tide gauges and satellite-derived EOT20 model are roughly consistent in the East China Sea: (1) The largest radiational S-2 amplitude can be as high as 14 cm. (2) Radiational and astronomical S-2 tidal amplitudes are large in the coastal zones but small in the open sea. (3) Radiational S-2 amplitudes are similar to 12% of astronomical S-2 amplitudes while phase differences between radiational and astronomical S-2 tides are similar to 114 degrees. The inconsistency between coastal tide gauges and EOT20 model in coastal zones should be induced by the temporal evolution of tides and the inaccuracy of satellite altimeter observations in this region. Furthermore, the methods used in the East China Sea can be easily applied to other sea areas, except diurnal resonant sea areas where the smooth nature of semi-diurnal admittances may be corrupted by nonlinear interactions between anomalously large diurnal tides.