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61.
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
62.
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
63.
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
64.
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
65.
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
66.
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
67.
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
68.
Abstract. The Pongkor Gold‐Silver Mine, Bogor district, West Java, is approximately 80 km southwest of Jakarta. The gold and silver mineralization in the area is present in a deposit consisting of an epithermal vein‐system named individually as the Pasir Jawa, Gudang Handak, Ciguha, Pamoyanan, Kubang Cicau, and Ciurug veins. In the area studied, rocks of basaltic‐andesitic composition are dominated by volcanic breccia and lapilli tuff, with andesite lava and siltstone present locally. The hydrothermal alteration minerals in the Ciurug area are typical of those formed from acid to near‐neutral pH thermal waters, where the acid alteration is distributed from the surface to shallow depth, while the near‐neutral pH alteration becomes dominant at depths. The Ciurug vein shows four main mineralization stages where each discrete stage is characterized by a specific facies; these are, from early to late: carbonate‐quartz, manganese carbonate‐quartz, banded‐massive quartz and gray sulfide‐quartz facies. The major metallic minerals are pyrite, sphalerite, chalcopyrite and galena; they occur in almost each mineralization stage. Bornite was observed only in the southern part of the Ciurug vein at a depth of 515 m, and the occurrence of this mineral is reported here for the first time. Electrum and silver sulfides (mostly acanthite) are minor, whereas silver sulfosalts, stromeyerite and mckinstryite, and covellite are in trace amounts. The silver sulfosalts have compositional ranges of pearceite, antimon‐pearceite and polybasite. Most of the electrum occurs coexisting with other sulfide minerals, as inclusions in pyrite grains, with very little as inclusions in chalcopyrite or sphalerite. Gold grades within the Ciurug vein vary from 1.2 to hundreds of ppm, where the highest gold grade occurs in the latest mineralization stage in a thin sulfide band in vein quartz. Fluid inclusion microthermometry of calcite and quartz indicates deposition throughout the mineralized veins in the range from 170 to 230d?C and from low salinity fluids (predominantly lower than 0.2 wt% NaCl equiv.). Fluid inclusions occur with features of boiling. 相似文献
69.
Abstract. The Francis Creek area located at the Sybil graben in North Queensland, Australia, has some features of epithermal gold mineralization such as gold-bearing quartz vein and silica body hosted in rhyodacitic rocks of the Late Carboniferous Hells Gate Formation. In order to understand the nature of the paleo-hydrothermal activity in this area and to aid exploration for an economic gold deposit in this area, we carried out hydrothermal alteration mapping surrounding the veins and silica body, over an area of about 7 times 5 km2 .
We defined two alteration zones and inferred the center of hydrothermal activity. Fluid inclusion shows the boiling feature, and the microthermometry analysis resulted in the trapping temperature of 240°C and low salinity. This temperature is consistent with the formation temperature of clay mineral in the host rocks. On the basis of whole-rock composition, the silica body was identified as silicified rocks. Precious metal minerals such as electrum and acanthite coexist with sulfide minerals. Iodagylite was identified as a product of weathering. The sulfide minerals imply that the low-sulfidation epithermal gold mineralization occurred in the Francis Creek area. 相似文献
We defined two alteration zones and inferred the center of hydrothermal activity. Fluid inclusion shows the boiling feature, and the microthermometry analysis resulted in the trapping temperature of 240°C and low salinity. This temperature is consistent with the formation temperature of clay mineral in the host rocks. On the basis of whole-rock composition, the silica body was identified as silicified rocks. Precious metal minerals such as electrum and acanthite coexist with sulfide minerals. Iodagylite was identified as a product of weathering. The sulfide minerals imply that the low-sulfidation epithermal gold mineralization occurred in the Francis Creek area. 相似文献
70.
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