The amplification mechanism of a meteo-tsunami originating off the western coast of Kyushu Island of Japan

A meteo-tsunami is a tsunami-like phenomenon excited by a traveling atmospheric disturbance. In Japan, meteo-tsunamis are frequently observed along the western coast of Kyushu Island during winter–spring. One of the largest meteo-tsunami occurred on March 3, 2010, where the maximum amplitude of water level oscillations exceeded 1 m in various bays on the western coast of Kyushu Island including Nagasaki Bay and Makurazaki Bay. Simultaneously, triangular-shaped rapid atmospheric pressure changes with amplitudes of ~1 hPa were recorded at various weather stations along the western coast of Kyushu Island.

We numerically reproduce large sea level oscillations in both bays assuming that a simple atmospheric pressure disturbance consisting of several triangular-shaped pressure changes in 10-20 min propagated east-southeastward at a speed of ~30 m/s over the East China Sea. Over a wide area of the shallow continental shelf in the East China Sea, oceanic waves are amplified through a resonant coupling (Proudman resonance) to the traveling atmospheric disturbance. Oceanic waves propagate eastward while being further amplified through reflection and refraction owing to the complicated topographic and configuration constraints in the coastal area and excite meteo-tsunamis along the western coast of Kyushu Island. Off Nagasaki Bay, the eigen-oscillaions formed on the continental shelf surrounded by the northwestern coast of Kyushu Island and Goto Islands supply oceanic waves resonant with the first mode oscillation in Nagasaki Bay. Off Makurazaki Bay, on the other hand, the reflection of oceanic waves (edge waves) from the end of the elongated continental shelf running east-west off Makurazaki Bay plays a key role in amplifying water level oscillations, which continues to supply water waves that are resonant with eigen-oscillations in Makurazaki Bay.