Ayumi Saruwatari

EVOLUTION OF THE 2011 TOHOKU EARTHQUAKE TSUNAMI ON THE PACIFIC COAST OF HOKKAIDO

A numerical computation of the 2011 Tohoku earthquake tsunami was performed to identify fundamental features of the tsunami evolution along the coast of Hokkaido, Japan. Edge waves formed at multiple locations where the refracted tsunami focused, governing local surface oscillations and regional variations in tsunami height along the Pacific coast of Hokkaido. The computation reasonably reproduced the distribution of surveyed tsunami height as well as the time records of surface elevation recorded at ports in Hokkaido. The major features of the frequency spectrum for the 2011 Tohoku tsunami were identical to those for the 2003 Tokachi-oki earthquake tsunami; inherent local properties of surface oscillation caused by the passage of edge waves existed, determined by the local bathymetry.

Report on the 2014 Winter Cyclone Storm Surge in Nemuro, Japan

From Tuesday, 16 December 2014, until Thursday, 18 December 2014, Hokkaido was battered by strong winds and high sea waves caused by a passing low pressure system intensified to typhoon levels. In the city of Nemuro, a rise in sea level influenced by the storm surge which exceeded quay height in port areas was observed from predawn Wednesday, 17 December 2014. Flooding was experienced in areas of central Nemuro, the Nemuro Port and estuaries of rivers. This technical note provides a comprehensive meteorological analysis and the results of a local flood survey carried out by the authors from 19 to 21 December 2014, and summarizes the characteristics of the 2014 Nemuro storm surge disaster.

LASER INDUCED FLUORESCENCE MEASUREMENTS OF CARBON DIOXIDE DISSOLUTION IN WAVE-BREAKING TURBULENCE

INTRODUCTION Air-sea gas transfer at equilibrium wave/wind state has been conventionally estimated using a simple model parameterized by only wind velocity over ocean (e.g. Liss and Merilvat 1986). However, local gas dissolution and transfer depend on other wave-breaking induced factors: turbulent intensity, breaker type, aeration effects etc, which are excluded in the conventional models. Toba and Koga (1986) presented an important role of wave breaking to affect air-sea gas and material exchanges in deep ocean. Komori et al. (1989) found that sub-surface turbulence disturbs and renews the air-water interface dissolved gas to entrain to depths. This surface renewal is a major process to induce downward gas flux under braking waves which significantly produce strong turbulence in the vicinity of the surface (Watanabe and Mori 2008). Another major factor enhancing the gas transfer is aeration in breaking waves. Numbers of air bubbles entrained through a wave splashing process significantly increase total area of air-sea interfaces per unit volume and enhance the gas dissolution into sea. For accurately estimating local C0 2 flux across the air-sea interface, dissolution and transport processes of CO2, which are also subjected to physical process of wave breaking, has to be understood. Mori (2004) presented capabilities of two-color laser induced fluorescence (LIF) image measurement that visualizes spatial distributions of dissolved C0 2 with dynamic correction of laser attenuation. In this study, the two-color LIF was applied to breaking waves for finding roles of the entrained air bubbles and

EFFECTS OF WAVE, TIDAL CURRENT AND OCEAN CURRENT COEXISTENCE ON THE WAVE AND CURRENT PREDICTIONS IN THE TSUGARU STRAIT

The Tsugaru Strait between Hokkaido and Honshu islands, connecting the Pacific Ocean and Japan Sea, has been used for shipping and fishery. The current in the strait formed by a tidal current and ocean current so-called Tsugaru Warm Current is recently assumed to be one of the potential renewable energy source in Japan. The present study investigates the effects of the coexistence of the tidal/ocean currents as well as sea waves on the predictions of the physical conditions around this strait. We performed two different numerical experiments for characterising the physical environment associated with current-current and wave-current interactions. Harmonic analysis of the tidal current shows tidal ellipses of the diurnal and semi-diurnal constituents are stretched into the direction of the ocean current and enable to be reasonably predicted without considering the effect of the current-current interaction. Wave height in the strait is shown to vary 0.75-1.5 times of the original wave height by attenuated and amplified by the coexisting current. It will be indicated that the physical environment associated with the current-current and wave-current interactions should be considered for effective utilisation of this area.

TURBULENT BEHAVIOR OF FLUIDIZED SEDIMENTS IN COMPOSITE SHEAR FLOW

A particle imaging measurement of granular particles was applied to fluidized and suspended solid particles involved in steady and unsteady shear flows. In this measurement, 42% sodium iodide solution was used as a fluid medium to coincide the refraction index with the transparent bed material (silica gel). Therefore, the vertical distributions of the granular velocity and turbulent behavior within the bed can be measured by tracking the dyed particles mixed with the bed material. The turbulent kinetic energy in the fluidized layer and particle concentration can also be measured using this technique. The turbulence developed over the bed disturbed the bed material, and as a result the surface particles were lifted and suspended. The underlying mechanism of fluidization and suspension of the sediment seabed in complex turbulent shear flow is believed to be understood through further parametric studies based on the present imaging technique.