Li-Ching Lin, Chin H. Wu

On October 15, 2013, unexpected meteotsunamis occurred prior to Typhoon Wipha located the distance of ~1,100 km from the center of the cyclone to the Tokyo bay. The occurrences were observed around the east coast of Japan coincidentally with atmospheric pressure disturbances induced by this typhoon. The observed wave height of meteotsunamis was up to ~0.5 m with the pressure fluctuation of ~2 hPa before this approaching typhoon. This study reveals the causes of the unexpected metetotsunamis in association with atmospheric forcings of the typhoon. The possible origin is identified from typhoon activities at the outer circulation that produced traveling pressure disturbances as a driving force to generate meteotsunamis. The causality of meteotsunami is revealed by time-frequency analysis of water level, atmospheric pressure, and wind speed. Results show that a combination of atmospheric forcings, pressure and wind stress, is responsible for the onset of meteotsunamis. The pressure fluctuation is found to be an indicator to determine the origin of atmospheric forcings and the formation of corresponding meteotsunamis when the meteorological condition is relative calm before a typhoon.