Nodal variations and long‐term changes in the main tides on the coasts of China

Abstract

The long-term changes in the main tidal constituents (O 1 , K 1 , M 2 , N 2 , and S 2 ) along the coasts of China and in adjacent seas are investigated based on 17 tide-gauge records covering the period 1954-2012. The observed 18.61 year nodal modulations of the diurnal constituents O 1 and K 1 are in agreement with the equilibrium tidal theory, except in the South China Sea. The observed modulations of the M 2 and N 2 amplitudes are smaller than theoretically predicted at the northern stations and larger at the southern stations. The discrepancies between the theoretically predicted nodal variations and the observations are discussed. The 8.85 year perigean cycle is identifiable in the N 2 parameters at most stations, except those in the South China Sea. The radiational component of S 2 contributes on average 16% of the observed S 2 except in the Gulf of Tonkin, on the south coast, where it accounts for up to 65%. We confirmed the existence of nodal modulation in S 2 , which is stronger on the north coast. The semidiurnal tidal parameters show significant secular trends in the Bohai and Yellow Seas, on the north coast, and in the Taiwan Strait. The largest increase is found for M 2 for which the amplitude increases by 4-7 mm/yr in the Yellow Sea. The potential causes for the linear trends in tidal constants are discussed.

Sea Level Acceleration in the China Seas

“…The effects of 18.61 years of the lunar nodal cycle on the SLA estimation have been investigated in the past for its considerable amplitude in the study area [8,[48][49][50][51] 18.61 in Equation (1), and a A 2`B2 denotes the amplitude of the lunar nodal cycle). Table 2 lists the SLA calculated from least squares fitting (Equation ( Note that in long records, the lunar cycle has little influence on the calculated acceleration, but in shorter records the results can be strongly affected by this cycle if it is not removed, as demonstrated in Table 2.…”

The Tides They Are A‐Changin': A Comprehensive Review of Past and Future Nonastronomical Changes in Tides, Their Driving Mechanisms, and Future Implications

“…Only over the past 20 years (since the digitization, concatenation, and public dissemination of regional and global databases of tide gauge records; Woodworth et al, ) has it been determined that significant and widespread positive and negative trends in tidal levels (and tidal currents) are occurring at many locations around the world (e.g., Devlin et al, ; Feng et al, ; Flick et al, ; Jay, ; Müller et al, ; Ray, ; Talke et al, ; Talke & Jay, ; Woodworth, ). Remarkably, the rates of tidal level changes observed are of similar magnitudes to the rate of mean sea level (MSL) rise at some sites; for example, Mawdsley et al () found increases in tidal range at Astoria (USA), Wilmington (USA), Delfzijl (the Netherlands), Cuxhaven (Germany), and Calais (France) of >25 cm over the last century.…”

Tidal Variability Related to Sea Level Variability in the Pacific Ocean

“…Recent work has shown that tides are evolving at diverse rates worldwide without any apparent relationship to astronomical forcing (Haigh et al, ; Mawdsley et al, ; Müller et al, ; Woodworth, ). On a regional scale, changes in major diurnal and semidiurnal tides have been observed in the Eastern Pacific (Jay, ), in the Gulf of Maine, (Ray, ), in the North Atlantic (Müller, ; Ray, ), in China (Feng et al, ; Feng & Tsimplis, ), in Japan (Rasheed & Chua, ), and at Pacific islands, though a reduction in gauge timing errors over time can cause spurious increases in amplitude (Zaron & Jay, ).…”