Global surface layer salinity change detected by Argo and its implication for hydrological cycle intensification   总被引：1，自引：0，他引：1  

Shigeki Hosoda  Toshio Suga  Nobuyuki Shikama  Keisuke Mizuno 《Journal of Oceanography》2009,65(4):579-586

We investigated changes in the global distribution of surface-layer salinity by comparing 2003–2007 Argo-float data with annual mean climatological surface-layer salinity data for 1960–1989 from the World Ocean Database 2005. The two datasets showed similar patterns, with low values in subpolar and tropical regions and higher values in the subtropics. The recent Argo data indicate that the contrast between low and high salinity has intensified in all areas except the subpolar North Atlantic. The intensified contrast of the surface layer salinity was maintaining for 2003–2007. Using a simple method, we attempted to estimate evaporation and precipitation changes on the basis of surface-layer salinity changes. The results show a high probability that the global hydrological cycle has increased in the past 30 years.  相似文献   

Primordial helium isotope signature from Plio–Quaternary alkaline basalts in Yemen     

Yuji Orihashi  Keisuke Nagao  Ashraf Al-Jailani  Barry B. Hanan 《Island Arc》2001,10(2):145-157

Abstract Isotopic compositions of He, Ne and Ar were measured on Plio–Quaternary alkaline basalts of Marib–Sirwah and Shuqra volcanic fields in Yemen, south-western Arabian Peninsula. Very high ³He/⁴He isotope ratios were found in olivine phenocrysts of some Quaternary alkaline basalts in both volcanic fields, located on the margin of the dispersed Afar mantle plume, compared with the Afar–Ethiopian province in the center of the mantle plume. This suggests that the Afar mantle plume source may consist of common component (C or focal zone (FOZO)) with variable primordial ³He/⁴He ratio rather than high μ mantle (HIMU) component. The three component mixing C as the Afar mantle plume, depleted mantle (DM) as upper mantle and lithospheric mantle with a hybrid enriched mantle I–II (EM I–EM II) characteristics may be adequate to explain He–Sr–Nd–Pb isotope variation for the Afar–Arabian Cenozoic volcanics. The occurrence of high ³He/⁴He ratios in the Marib–Sirwah volcanic field appears to show that the primitive basaltic magma, derived from the margin of the dispersed trous-like Afar mantle plume during 15–0 Ma, was not by contamination of lithospheric and upper mantle materials in comparison with that from the center of the Afar mantle plume as a result of relatively low thermal anomaly.  相似文献   

Mesoscale current fluctuations observed in the deep western North Pacific     

Shiro Imawaki  Keisuke Taira  Toshihiko Teramoto 《Journal of Oceanography》1984,40(1):39-45

A set of simultaneous long-term, deep current measurements was taken using a moored array in the mid-ocean of the western North Pacific near 30°N, 146°E. Five current meters at three stations provided good quality records over 84 days. Low-frequency current fluctuations with meridional dominance are clearly seen in the deep layer records. They are consistent with signals of a mesoscale current fluctuation which has a period of about 100 days, an east-west wave length of about 200 km, and a westward phase propagation with a speed of about 2 cm sec^–1. Bottom intensification of the east component of low-frequency current fluctuations is also observed.  相似文献   

Variability of Upper Ocean Heat Balance in the Shikoku Basin during the Ocean Mixed Layer Experiment (OMLET)     

Hirotaka Otobe  Keisuke Taira  Shoji Kitagawa  Tomio Asai  Kimio Hanawa 《Journal of Oceanography》2003,59(5):619-627

The heat balance of the surface layer in the vicinity of the former Ocean Weather Station “Tango” (OWS-T; 29°N, 135°E), where a large amount of heat is transported by the Kuroshio and transferred to the atmosphere, was studied by during Ocean Mixed Layer Experiment (OMLET) as an oceanographic component of the Japanese World Climate Research Program (1987–1991). Temperature and velocity in the upper ocean measured using a surface moored buoy system deployed by the Ocean Research Institute, the University of Tokyo, in total 668 days of four time series namely the periods of April 1988–November 1988 (OMELET-88), August 1989–February 1990 (OMLET-89), April 1990–September 1990 (OMLET-901) and September 1990–January 1991 (OMLET-902). We have analyzed the moored buoy data of the upper 100 m for the latter three time series (OMLET-89, -901 and -902) and here we discuss the heat balance of the upper 100 m, in combination with surface heat flux and oceanographic data provided by the Japan Meteorological Agency. A large fluctuation of oceanic heat convergence/divergence of 200–300 W/m² in amplitude with predominant period of 20–30 days occurred in the first half of OMLET-89 period, which was just the early stage in the formation process of a large meander path of the Kuroshio. A large amount of heat convergence of 71 and 79 W/m² on average was detected in observation period of OMLET-89 and -901, respectively. During OMLET-902, relatively small heat convergence of 13 W/m² was obtained. It is suggested that these variations of oceanic heat convergence in this region were closely related to the fluctuation of the Kuroshio axis to the south of Japan. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Observation of temperature and velocity in the coastal water off Kuala Terengganu,Malaysia     

Keisuke Taira  Mohd Nasir B. Saadon  Shoji Kitagawa  Tetsuo Yanagi 《Journal of Oceanography》1996,52(2):251-257

Mooring observation of current and temperature was made at 17.8 m layer of 19 m depth about 8 km east to Kuala Terengganu, Peninsular Malaysia. Harmonic analysis was applied to tidal currents for 30 days in September 1993, and to the tides observed at Chendering. The K1 tide was the largest both in tidal currents and the tides. Daily mean temperature, currents, sea level, and winds were analyzed from September 1993 to May 1994. Northeast Monsoon from December to February caused sea level rise of 50 cm and temperature lowering of 1°C.  相似文献   

Path and volume transport of the Kuroshio current in Sagami Bay and their relationship to cold water masses near Izu Peninsula     

Keisuke Taira  Toshihiko Teramoto 《Journal of Oceanography》1986,42(3):212-223

The path of the Kuroshio in Sagami Bay was surveyed through drifter tracking from Oshima-West Channel to Oshima-East Channel. A subsurface drifter with a drogue at 300 m depth flowed around Oshima from Oshima-West Channel to Oshima-East Channel. A difference in flow directions between the upper and lower layers was apparent in the northwest of Oshima. Flow directions there were shown to change from north in the surface layer to east in the bottom layer, and this was confirmed with moored currentmeters.A profile of northward current velocity was estimated from measurements in six layers with currentmeters deployed in the Oshima-West Channel. The profile shows a core of northward flow along the eastern bottom slope and a weak southward flow along the western bottom slope. Volume transport of the Kuroshio into Sagami Bay was estimated to be 1.8×10⁶m³sec^–1 from the profile.Long-term current measurement showed that southward flows were observed in Oshima-West Channel in July 1977, May 1978 and April 1979. Cold or warm water masses appearing south of the Izu Peninsula are suggested to have caused the changes.Displacement of the cold water mass in July 1977 is discussed on the basis of current measurements and offshore oceanographic conditions.  相似文献   

A field study of the development of wind-waves     

Keisuke Taira 《Journal of Oceanography》1972,28(5):187-202

This paper presents the results of observation on the development of wind-waves which were generated in a lake water about 420 cm deep with a fetch 12 km long. Measurements of surface elevation were carried out at the end of an observational pier where the water depth was 80 cm. The wave momentum flux, i.e., the growth rate of the wave momentum, was estimated from both significant waves and power spectral densities for the wave records. The values obtained by the two ways accorded fairly well and they were 57 % as large as the wind stress measured simultaneously. The exponential growth rate of spectral densities for a frequency component was in good accord with that observed bySnyder andCox (1966) and by others. If these growth rates are applied to all the components of the spectrum, the wave momentum flux must exceed the wind stress. This cannot explain the experimental results nor can be physically accepted. The difference of spectral densities between the two successive runs showed that the increase of spectral densities was. limited in several bands of frequency. The phenomena are discussed in relation with the overshoot-undershoot effects studied byBarnett andSutherland (1968).Observational results suggest that the spectral growth of a certain component is closely related to the spectral densities of other components. Energy exchange among componented waves has not been considered in the theories for generation and development of wind-waves established by Phillips, Miles and others.New generation mechanism suggested byLonguet-Higgins (1969) was found to be able to describe the observed growth rates of the form(f)={(1/2)(t–t_1/2)}²: the spectral density(f) was proportional to the square of durationt. However, the mechanism can not explain the overshoot-undershoot effects peculiar to the equilibrium spectrum of windwaves.Three frequencies characterizing the discrete distributions of frequency bands where spectral densities increased were examined and three waves corresponding to these frequencies were found to be satisfying the resonance conditions for the wave-wave interactions among three sinusoidal wave trains as studied byPhillips (1960),Longuet-Higgins (1962) andBenny (1962). The interactions are suggested to predict well both the spectral growth proportional to squares of duration and the ceaseless oscillations of spectral densities in an equilibrium spectrum.  相似文献   

A coastal acoustic tomography experiment in the Tokyo Bay   总被引：1，自引：0，他引：1  

KANEKO Arat  YAMAGUCHI Keisuke  YAMAMOTO Tokuo  GOHDA Noriaki  ZHENG Hong  SYAMSUDIN Fadli  LIN Ju  NGUYEN Hong-Quang  MATSUYAMA Masaji  HACHIYA Hiroyuki  HASHIMOTO Noriaki 《海洋学报(英文版)》2005,24(1):86-94

Eight sets of coastal acoustic tomography (CAT) systems were deployed during November 29 to December 10, 2002 at the coasts on both sides of Tokyo Bay to measure tidal current structures at 15-rain interval.Sound transmission across the Tokyo Bay (between Yokohama and Chiba)was successfillly traced,even under severe interference from ship generated wakes and bubbles.Tidal current fields changing from northward to southward flow are well reconstructed by the inverse analysis of travel-time difference data for a period with the best sound transmission condition. It is suggested that the CAT is the most powerful tool to continuously map tidal current fields in the coastal seas with heavy shipping traffic and fisheries activity.  相似文献   

Petrological models of the oceanic lithosphere: Geophysical and geochemical tests     

Keisuke Ito 《Earth and Planetary Science Letters》1974,21(2):169-180

Petrological models of the oceanic lithosphere are tested to satisfy geophysical and geochemical constraints within the framework of plate tectonics. Quartz eclogite, olivine eclogite, peridotite and dunite are considered as the material of the lithosphere. The temperature at the base of the lithosphere is assumed to be the solidus temperature. This temperature, the thermal conductivity, and the heat flow and topography changes with age are used as the geophysical constraints. The compressional wave velocity-depth profile is used to select preferred models. Among geophysically successful models, high-temperature models are preferred to wet low-temperature models, because the low-temperature models have difficulties in explaining the mechanism of generation of oceanic basalt magmas. A preferred model is a two-layer model 70 km thick consisting of peridotite at the upper lithosphere and olivine eclogite at the lower lithosphere bounded at the base by the dry solidus.  相似文献   

Multifractal analysis of earthquakes   总被引：5，自引：0，他引：5  

Tadashi Hirabayashi  Keisuke Ito  Toshikatsu Yoshii 《Pure and Applied Geophysics》1992,138(4):591-610

Multifractal properties of the epicenter and hypocenter distribution and also of the energy distribution of earthquakes are studied for California, Japan, and Greece. The calculatedD _q-q curves (the generalized dimension) indicate that the earthquake process is multifractal or heterogeneous in the fractal dimension. Japanese earthquakes are the most heterogeneous and Californian earthquakes are the least. Since the earthquake process is multifractal, a single value of the so-called fractal dimension is not sufficient to characterize the earthquake process. Studies of multifractal models of earthquakes are recommended. Temporal changes of theD _q-q curve are also obtained for Californian and Japanese earthquakes. TheD _q-q curve shows two distinctly different types in each region; the gentle type and the steep type. The steeptype corresponds to a strongly heterogeneous multifractal, which appears during seismically active periods when large earthquakes occur.D _q for smallq or negativeq is considerably more sensitive to the change in fractal structure of earthquakes thanD _q forq2. We recommend use ofD _q at smallq to detect the seismicity change in a local area.  相似文献