Tsunami ascending in rivers as an undular bore     

Yoshinobu Tsuji  Takashi Yanuma  Isao Murata  Chizuru Fujiwara 《Natural Hazards》1991,4(2-3):257-266

At time of the 1983 Japan Sea tsunami, waves in the form of a bore ascended many rivers. In some cases, bores had the form of one initial wave with a train of smaller waves, and in other cases, such a wave train did not appear and only a step with a flat water surface behind was observed. In the present study, it is clarified that both undular-type and nonundular-type bores can be recognized as solutions of the KdV-Burger's equation which was introduced by Johnson in 1972. Numerically obtained analytical solutions and results of laboratory experiments are compared.  相似文献   

Damage to coastal villages due to the 1992 Flores Island earthquake tsunami     

Yoshinobu Tsuji  Hideo Matsutomi  Fumihiko Imamura  Minoru Takeo  Yoshiaki Kawata  Masafumi Matsuyama  Tomoyuki Takahashi  Sunarjo  Prih Harjadi 《Pure and Applied Geophysics》1995,144(3-4):481-524

A field survey of the 1992 Flores Island earthquake tsunami was conducted during December 29, 1992 to January 5, 1993 along the north coast of the eastern part of Flores Island. We visited over 40 villages, measured tsunami heights, and interviewed the inhabitants. It was clarified that the first wave attacked the coast within five minutes at most of the surveyed villages. The crust was uplifted west of the Cape of Batumanuk, and subsided east of it. In the residential area of Wuring, which is located on a sand spit with ground height of 2 meters, most wooden houses built on stilts collapsed and 87 people were killed even though the tsunami height reached only 3.2 meters. In the two villages on Babi Island, the tsunami swept away all wooden houses and killed 263 of 1,093 inhabitants. Tsunami height at Riang-Kroko village on the northeastern end of Flores Island reached 26.2 meters and 137 of the 406 inhabitants were killed by the tsumani. Evidence of landslides was detected at a few points on the coast of Hading Bay, and the huge tsunami was probably formed by earthquake-induced landslides. The relationship between tsunami height and mortality was checked for seven villages. The efficiencies of trees arranged in front of coastal villages, and coral reefs in dissipating the tsunami energy are discussed.  相似文献   

Frequency-wavenumber spectra of equatorial waves detected from satellite altimeter data     

Yoshinobu Wakata 《Journal of Oceanography》2007,63(3):483-490

The sea surface height anomaly in the Pacific equatorial area was separated into equatorial modes using satellite altimeter data. The power-spectral density (PSD) was obtained for the east-west wavenumber and frequency for each separated mode. The PSD distribution was compared with the theoretical dispersion curve for the equatorial modes derived by Matsuno (1966). The first Rossby modes have a high-density distribution that is slightly lower than the theoretical dispersion curve, but the Kelvin mode and the higher Rossby modes have high-density distribution that almost matches each dispersion curve. Results of analyses of satellite observational data show that wave motion near the equator mainly shows characteristics of equatorial waves, especially for a intraseasonal time scale.  相似文献   

Variability of the Sea Surface Salinity (SSS) in the Western Tropical Pacific: On the Ability of an OGCM to Simulate the SSS, and on the Sampling of an Operating Merchant Ship SSS Network     

Mansour Ioualalen  Yoshinobu Wakata  Yoshikazu Kawahara  Yves Gouriou  David Varillon 《Journal of Oceanography》2003,59(1):105-111

The sea surface salinity (SSS) derived from a network developed at Institut de Recherche pour le Développement (IRD/Nouméa) has been analyzed during the period 1995–1998 in the tropical western Pacific. The measurements were made with thermosalinographs installed on merchant ships selected for their regularity and routes. The western tropical Pacific was sampled mainly along three regular routes across the equator leading to an average of a one month frequency. We analyze here how such a network can be efficient in monitoring the SSS at time scales longer than one month. For this purpose we have used results derived from the Princeton Ocean Model (POM) which is forced by the surface flux of National Centers for Environmental Prediction (NCEP) reanalysis data. The interannual variability of the simulated SSS exhibits very similar features to (sub-sampled) observations despite its being weakly damped to a climatology in order to avoid biases. Even smaller time scale phenomena can be simulated, like the erosion/reconstruction of the region composed of low density waters lying within the Pacific warm pool. The agreement between the observational data and the simulations indicate that the network sampling is sufficient to monitor the SSS variability of the western tropical Pacific from three-month to interannual time scales. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Kelvin Waves Excited by Intraseasonal Wind Forcing     

Yoshinobu Wakata 《Journal of Oceanography》2001,57(6):693-707

The Kelvin wave excited by an intraseasonal wind forcing with a 40-day period over the western Pacific Ocean was simulated using an ocean general circulation model, and was investigated by the use of spectral analysis. The amplitude of the temperature has two peaks north and south of the equator at the depth of the thermocline, and the amplitude of zonal velocity also has two peaks on the equator above and below the thermocline. The phase shows the upward propagation of the wave. It was queried why this wave, which appears to be transient rather than modelike, is formed quickly and always propagates with a phase velocity of about 3 m/s. The vertical one-dimensional forcing problem was studied, where the external forcing of up and down motions moving eastward is imposed at the surface. The growth time is estimated from the resonant solution. The first mode can resonate quickly, but the second cannot. The response in the infinitely deep ocean was also studied to focus on the transiency, where the reflection from the bottom is inhibited. The wave response to the forcing with a speed of about 3 m/s has a large amplitude, i.e. quasi-resonance occurs. In this case, the thermocline plays the role of a reflector, and the upper ocean between the sea surface and the thermocline behaves as a duct. Here, the small resonant cavity explains why the wave is formed so quickly, and the special value of the wave velocity is interpreted as a resonance condition in the duct. The wave corresponding to the second baroclinic mode could not be excited easily by the short-lived forcing at the surface, since this mode is mainly structured under the thermocline. It was found that the wave damps in consequence of leaking energy downward, and the damping rate depends on the period of the wave. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Automated identification of red tide phytoplanktonProrocentrum triestinum in coastal areas by image analysis     

Takashi Tsuji  Takashi Nishikawa 《Journal of Oceanography》1984,40(6):425-431

An image analyzing system was developed for automated identification and cell counting of a red tide phytoplankton,Prorocentrum triestinum, in coastal areas. Using an interference filter, a photograph of phytoplankton was taken through a fluorescence microscope. The photograph was then fed into an image analyzing system consisting of an image sensor, a front mini-computer, and a host computer. The system identifiedP. triestinum as effectively as the conventional method in one twentieth of the time required by the latter. The system was used to examine preserved samples collected fromP. triestinum-dominated red tides in Tokyo Bay. It was found that there were two phytoplankton populations in the red tide:P. triestinum and a smaller phytoplankton.  相似文献   

The tsunami of 3 February 1605     

Hisashi Miyoshi  Kaname Satoh  Yoshinobu Tsuji 《Journal of Oceanography》1989,45(3):174-180

Whether the origins of the tsunami of 3 February 1605 were separated ones or a joined one, is one of the most important problems for Japanese society. When the marine knowledge has not been popularized, it has been considered that the damage pattern on Hachijo Island (including Kojima) was an important key to solving this question.It resembles the situation that the reports concerning the tsunami of 1 April 1946 were introduced to Japanese society under an internal disturbance just after the war, and we overlooked the most important consideration on the combination of tsunami and storm waves caused by the trade wind, and received this tsunami as an extraordinarily huge one.We studied the statistics of recent wind directions around Hachijo Island in January and February 1973, 1974, 1977, 1983, 1984, 1985, 1986 and 1987. And we believed that the probability was high that we could explain well that the damage pattern on Hachijo Island in 1605 was due to the combination of tsunami and storm waves caused by the monsoon.We need not, therefore, look back the damage pattern on Hachijo Island when we consider the fact that the necrologies of many temples in Shizuoka Prefecture record no death on 3 February 1605, proves to be the key to infer that the origins were separated ones.  相似文献   

Misfit functionals in Laplace‐Fourier domain waveform inversion,with application to wide‐angle ocean bottom seismograph data     

Rie Kamei  R. Gerhard Pratt  Takeshi Tsuji 《Geophysical Prospecting》2014,62(5):1054-1074

In seismic waveform inversion, non‐linearity and non‐uniqueness require appropriate strategies. We formulate four types of L2 normed misfit functionals for Laplace‐Fourier domain waveform inversion: i) subtraction of complex‐valued observed data from complex‐valued predicted data (the ‘conventional phase‐amplitude’ residual), ii) a ‘conventional phase‐only’ residual in which amplitude variations are normalized, iii) a ‘logarithmic phase‐amplitude’ residual and finally iv) a ‘logarithmic phase‐only’ residual in which the only imaginary part of the logarithmic residual is used. We evaluate these misfit functionals by using a wide‐angle field Ocean Bottom Seismograph (OBS) data set with a maximum offset of 55 km. The conventional phase‐amplitude approach is restricted in illumination and delineates only shallow velocity structures. In contrast, the other three misfit functionals retrieve detailed velocity structures with clear lithological boundaries down to the deeper part of the model. We also test the performance of additional phase‐amplitude inversions starting from the logarithmic phase‐only inversion result. The resulting velocity updates are prominent only in the high‐wavenumber components, sharpening the lithological boundaries. We argue that the discrepancies in the behaviours of the misfit functionals are primarily caused by the sensitivities of the model gradient to strong amplitude variations in the data. As the observed data amplitudes are dominated by the near‐offset traces, the conventional phase‐amplitude inversion primarily updates the shallow structures as a result. In contrast, the other three misfit functionals eliminate the strong dependence on amplitude variation naturally and enhance the depth of illumination. We further suggest that the phase‐only inversions are sufficient to obtain robust and reliable velocity structures and the amplitude information is of secondary importance in constraining subsurface velocity models.  相似文献   

Symbiosis of Biodiversity and Tea Production Through Chagusaba     

KUSUMOTO Yoshinobu  INAGAKI Hidehiro 《资源与生态学报(英文版)》2016,7(3):151-154

Chagusaba, which is traditional tea-grass integrated system in Shizuoka, is one of Globally Important Agricultural Heritage Systems (GIAHS) sites in Japan. Chagusaba provide an important habitat for natural plant species. In this study, we investigated the flora in Chagusaba and environmental factors to affect the number of native species estimated their diversity. Fifty Chagusaba were classified in to five vegetation types by Two-way indicator species analysis. In addition, high number of native plant species Chagusaba had low soil pH, covered large areas, and were in places where the land had not been modified. Through statistical analysis (GLM), we found that land modification had an especially significant effect on the diversity of native plants, and that the diversity of native plants was reflected in the history of the use of the land.  相似文献   

Traditional Tea-grass Integrated System in Shizuoka as a GIAHS Site: Values and Conservation—Background of Application and Efforts after Registration     

Hidehiro INAGAKI  Yoshinobu KUSUMOTO 《资源与生态学报(英文版)》2019,10(5):511-517

The traditional tea-grass integrated system in Shizuoka is the first example of a Globally Important Agriculture Heritage Systems (GIAHS) site in Japan that was proposed by a local government. In this paper, we report the background and circumstances leading to the recognition of this system, its registration as a GIAHS, and its current use after registration. Although semi-natural grasslands have decreased considerably in Japan, we found unique semi-natural grasslands with no pest insects and a rich biodiversity around the tea fields. These grasslands and the farming method employed are known as “Chagusaba”, which was registered as a GIAHS in 2013. However, the registration process for GIAHS was not easy, as many local farmers do not understand the value of their traditional farming methods or the GIAHS honor. After registering Chagusaba as a GIAHS, our main agenda was branding. Traditional farming, with time and effort, produces high-quality tea. As labor saving technologies in agriculture have progressed in Japan, the price of high-quality tea has declined, and consequently, the numbers of farmers performing the inefficient traditional farming methods are decreasing. It is necessary to correctly brand the Chagusaba-grown tea and reflect the value of the traditional farming method in the price. The local government of the Shizuoka Prefecture is currently working on implementing a certification system, which includes scientific evaluation using GPS, and the introduction of biodiversity indicators.  相似文献