[A-OS14] Physical Oceanography (General)

[AOS14-P10] Estimation of the Highest and Lowest Astronomical Tides along the North Pacific Ocean Coast

*Wen-Hau Lan¹, Chung-Yen Kuo², Tzu-Pang Tseng² (1. Department of Civil Engineering, National Kaohsiung University of Science and Technology, 2.Department of Geomatics, National Cheng Kung University)

Keywords:lunar nodal cycle, highest astronomical tide, lowest astronomical tide, modified two-step harmonic analysis

The lunar nodal cycle, causing by variations in the Moon’s declination over an period of 18.61 years, induces modifications in the amplitude and phase shifts of global tidal constituents. However, the observed range in tidal amplitude is at present not yet well understood, and it is crucial for coastal hazard planning and chart datum. In this study, we aim to quantify the highest astronomical tide (HAT) along the North Pacific Ocean coast and analyze impact of the nodal tide, including potential variations in its amplitudes and phase alterations on the HAT that could be important as a scientific basis for future coastal disaster planning. Additionally, since there is no standard procedure of computing the Hight/Lowest Astronomical Tide (LAT) over the 18.61-year nodal cycle, we analyze the contributions of various factors for calculating the LAT, including time spans, sampling frequencies, number of tidal constituents, and nodal tide correction, and establish a standard procedure which was adopted in Taiwan. The HAT is calculated according to the LAT calculation procedure. Finally, a modified two-step harmonic analysis procedure is applied to re-evaluate the seasonality and slope variability of the major constituents (M₂, S₂, K₂, and O₁) along the North Pacific Ocean coast.