Decreasing trend of M2 tidal amplitude observed along northwestern Kyushu

Abstract:

Observations show that M₂ tidal amplitude is decreasing along the northwestern coast of Kyushu, Japan. However, the cause of this decrease is not well understood. Using data from the Japan Oceanographic Data Center (JODC) and Japan Meteorological Agency (JMA), we found that this decrease in M₂ tidal amplitude from 1980 to 2018 is about 4% on average. We also find a 10cm sea-level rise occurred during the same period. there appears to be a strong negative correlation between M₂ tidal amplitude and sea-level variability at each tidal gauge station.

We examined the effect of the sea level rise on the tidal resonance of the East China Sea based on idealized and realistic topographic numerical model experiments. Both experiments showed an amplitude decrease in the majority of the East China Sea and northwestern coast of Kyushu, but the magnitude change is much smaller than that observed. Our experiments suggest that at least 1m sea-level rise is needed to explain the observed M₂ tidal amplitude trend for 50 years through resonance.