Long-Wave Generation due to Atmospheric-Pressure Variation and Harbor Oscillation in Harbors of Various Shapes and Countermeasures against Meteotsunamis

Abstract

First, the generation and propagation of long ocean waves due to the atmospheric-pressure variation have been simulated using the numerical model based on the nonlinear shallow water equations, where the atmospheric-pressure waves of various pressure-profile patterns travel eastward over East China Sea. Before the oscillation attenuation in Urauchi Bay, Japan, the incidence of long waves can continue owing to an oscillation system generated between the main island of Kyushu and Okinawa Trough. Second, the simple estimate equations are proposed to predict both the wave height and wavelength of long waves caused by an atmospheric-pressure wave, using atmospheric-pressure data above the ocean. Third, numerical simulation has been generated for the oscillation in the harbors of C-, I-, Land nd T-type shapes, as well as Urauchi Bay with two bay heads like a Ttype harbor. Finally, we discuss disaster measures, including the real-time prediction of meteotsunami generation, as well as both the structural and the nonstructural preparations.

Numerical Simulation of Surface and Internal Wave Excitation due to an Air Pressure Wave

“…The waveform of the air pressure wave was an isosceles triangle, where the length of its base, i.e., the wavelength λ, was 10 km or 20 km. The maximum and minimum pressures p m of positive and negative air pressure waves, respectively, were 2 hPa and −2 hPa, respectively, referring the values in the meteotsunami and eruption cases [11,21]. The position of the air pressure wave center at the initial time, i.e., t = 0 s, was x 0 = 50 km.…”

“…Regarding surface waves, air pressure waves of a few hectopascals often generate meteotsunamis around the world, e.g., [7,8,9]. For example, at the west coasts of Kyushu, Japan, meteotsunamis called "Abiki" are observed, e.g., [10,11]. Conversely, internal waves are also generated and amplified by air pressure waves due to meteorological factors including typhoons [12,13].…”

Tsunamis Generated and Amplified by Atmospheric Pressure Waves Due to an Eruption over Seabed Topography

“…where η(x, t) and b(x) are the water surface displacement and seabed position, respectively, and ∇ is a horizontal partial differential operator, namely, (∂/∂x, ∂/∂y). The gravitational acceleration g is 9.8 m/s 2 , and the sea water density ρ is 1030 kg/m 3 .…”

“…After the atmospheric p wave W1 stopped traveling and a tsunami generated by W1 left from W1, the ma amplitude of the tsunami propagating as a free wave, namely, ηmax, was numeric tained. The calculated ηmax was compared with the estimated maximum amplitud corresponding tsunami under the linear shallow-water condition, namely, ζmax, wh obtained by Equation ( 8) in [3], i.e., ζmax = [pmax•(vpτ)/(λ/2)]/20000, where the units of atmospheric pressure, length, and time are Pa, m, and s, respec…”

“…After the eruption, the atmospheric Lamb wave with the largest pressure deviation of approximately 2 hPa was observed in Japan [1]. Therefore, one of the sources that caused the tsunamis observed far away from the eruption site was considered to be the Proudman resonance [2], which is also an origin of meteotsunamis, e.g., [3]. The tsunamis caused by atmospheric pressure fluctuations due to eruptions were studied for the 1883 Krakatau volcanic eruption tsunamis [4][5][6][7][8][9][10][11], as well as the 1956 Bezymianny volcanic eruption tsunamis [12,13].…”