Unexpected meteotsunamis prior to Typhoon Wipha and Typhoon Neoguri
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Unexpected meteotsunamis prior to Typhoon Wipha and Typhoon Neoguri Li‑Ching Lin1 · Chin H. Wu2 Received: 20 March 2020 / Accepted: 7 September 2020 © Springer Nature B.V. 2020
Abstract Two meteotsunamis were unexpectedly observed along the eastern coast of Japan coincidentally with atmospheric pressure disturbances prior to two typhoons, respectively. The maximum wave height of meteotsunamis was up to ~ 0.5 m in Aburatsubo Bay with the pressure fluctuation of ~ 2 hPa before Typhoon Wipha. This study reveals the causes of the unexpected meteotsunamis in association with atmospheric forcings of the typhoons. 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 meteotsunamis is revealed by time–frequency analysis of sea 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 relatively calm before a typhoon. Keywords Meteotsunamis · Typhoons · Atmospheric forcings · Tokyo Bay
1 Introduction Along the eastern coast of Japan, two meteotsunamis were unexpectedly observed before typhoon passages. On October 15, 2013, unexpected meteotsunamis occurred when Typhoon Wipha at a distance of ~ 1100 km from the center of the cyclone was approaching to the Tokyo Bay. Similarly, the second event was introduced by Typhoon Neoguri of 2019 at approximate 430 km southwest of the study area. During typhoons, strong storm surges and large wind waves locally produced by the low pressure centered at the cyclone (Marcos et al. 2019) are expected. Normally, warning for typhoon-induced flooding or other hazards are issued. However, the observed heights of such meteotsunamis were abnormally enhanced at least 12 h prior to the typhoons in this study. Specifically, meteotsunamis without any warning can * Li‑Ching Lin [email protected] 1
National Applied Research Laboratories, 3F., No. 106, Sec. 2, Heping E. Rd, Taipei 106, Taiwan
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Department of Civil and Environmental Engineering, University of Wisconsin-Madison, Madison, WI 53706, USA
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Natural Hazards
inundate coastal areas, overtop coastal structures, or even generate rip currents (Bechle and Wu 2014; Linares et al. 2019; Pattiaratchi and Wijeratne 2015; Monserrat et al. 2006) that cause people injury or even fatalities. In view of the safety concern, it is of interest and importance to better understand the occurrences, causes, and statistics of unexpected meteotsunamis before any typhoon events. Meteotsunamis are tsunami-like sea-level oscillations meteorologically induced by the traveling forcings with a rapid change of atmospheric pressures and winds disturbances (Bechle and Wu 2014; Monserrat et al. 2006;
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