Comparison of sea surface heights observed by TOPEX altimeter with sea level data at Chichijima     

Naoto Ebuchi  Kimio Hanawa 《Journal of Oceanography》1996,52(3):259-273

The sea surface heights (SSHs) observed by the TOPEX altimeter are compared with tide gauge data at Chichijima in Ogasawara (Bonin) Islands and hydrographic data taken around the islands, in order to quantitatively verify the altimeter observations and oceanic tide corrections by three tide models proposed by Cartwright and Ray (1991), Rayet al. (1994), and Maet al. (1994). First, performance of the new tide models is assessed by comparing tidal variations consisting of diurnal and semi-diurnal constituents with the tide gauge data at Chichijima. The tide model proposed by Rayet al. gives the smallest root-mean-squared (rms) difference of 2.61 cm. Errors in amplitude and phase in each tide model are evaluated by spectral analysis. The TOPEX SSHs corrected by the tide models are compared with sea level data at Chichijima. A long-term variation of a period of about 1 year is found in the residual between the SSHs and the Chichijima sea levels. This variation is also found in the difference between the dynamic height anomalies calculated from hydrographic data around the island and the Chichijima sea levels. By subtracting the long-term variation, the rms difference between the TOPEX SSHs and the Chichijima sea levels is reduced to about 4 cm and the slope of the regression line is improved to unity. The residual shows variations related to aliasing caused by incompleteness of the ocean tide correction with the repeat cycle of the altimeter observation.  相似文献   

Trajectory of Mesoscale Eddies in the Kuroshio Recirculation Region   总被引：4，自引：1，他引：4  

Naoto Ebuchi  Kimio Hanawa 《Journal of Oceanography》2001,57(4):471-480

Trajectories of mesoscale eddies in the Kuroshio recirculation region were investigated by using sea surface height (SSH) anomaly observed by the TOPEX/POSEIDON and ERS altimeters. Cyclonic and anticyclonic eddies have been traced on maps of the filtered SSH anomaly fields composed from the altimeter observations every ten days. Both the cyclonic and anticyclonic eddies propagate westward in the Kuroshio recirculation region from a region south of the Kuroshio Extension. The propagation speed of these eddies has been estimated as about 7 cm s⁻¹, which is much faster than the phase speed theoretically estimated for the baroclinic first-mode Rossby wave in the study area. It was also found that in the Izu-Ogasawara Ridge region, most of eddies pass through the gap between the Hachijojima Island and Ogasawara (Bonin) Islands, and some of the eddies decay around the Izu-Ogasawara Ridge. It seems that the trajectory of the eddies is crucially affected by the bottom topography. In the region south of Shikoku and east of Kyushu, some of the eddies coalesce with the Kuroshio. It is also suggested that this coalescence may trigger the path variation of the Kuroshio in the sea south of Japan. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Statistical properties of microwave backscattering from laboratory wind-wave surfaces     

Naoto Ebuchi  Hiroshi Kawamura  Yoshiaki Toba 《Journal of Oceanography》1992,48(2):139-154

The microwave backscattering from wind-wave surfaces is observed in a windwave tunnel under various conditions of the wind and wind waves, and its statistical features are investigated. The dependence of the backscattered power on the wind speed and the incident angle shows similar features to those predicted by models proposed previously. However, the dependence of the backscattered power on the incident angles also corresponds to the asymmetrical feature of the wind-wave surfaces with respect to the wind direction. The spectral analyses of time series of the backscattered intensity show that the propagating speed of fine structures of the wind-wave surface contributing to the backscattering at large incident angles does not coincide with the phase speed of the freely propagating Braggwaves. Atupwind incidence, the surface structures of wind waves contributing to the backscattering propagates with the dominant waves at their phase speed. This result is inconsistent with the two-scale model in which the Bragg waves are simply superimposed on longer waves, but is consistent with the results of optical observation by Ebuchiet al. (1987). At downwind incidence, the propagating speed is slower than the phase speed of the dominant waves.  相似文献   

Volume transport of the Soya Warm Current revealed by bottom-mounted ADCP and ocean-radar measurement   总被引：2，自引：2，他引：0  

Yasushi Fukamachi  Iori Tanaka  Kay I. Ohshima  Naoto Ebuchi  Genta Mizuta  Hideo Yoshida  Shiro Takayanagi  Masaaki Wakatsuchi 《Journal of Oceanography》2008,64(3):385-392

The vertical structure of the Soya Warm Current (SWC) was observed by a bottom-mounted acoustic Doppler current profiler (ADCP) in the region of the SWC axis near the Soya Strait during a 1-year period from May 2004. The ADCP data revealed a marked seasonal variability in the vertical structure, with positive (negative) vertical shear in summer and fall (winter and spring). The volume transport of the SWC is estimated on the basis of both the vertical structure observed by the ADCP and horizontal structure observed by the ocean radars near the strait. The transport estimates have a minimum in winter and a maximum in fall, with the yearly-averaged values in the range of 0.94–1.04 Sv (1 Sv = 10⁶ m³ s⁻¹). These lie within a reasonable range in comparison to those through other straits in the Japan Sea.  相似文献   

Dominant sea-surface temperature anomaly patterns in summer over the North Pacific ocean     

Nanase Motokawa  Noriyuki Matsuo  Naoto Iwasaka 《Journal of Oceanography》2010,66(4):581-590

We investigated the structure and persistency of the dominant sea-surface temperature (SST) anomaly pattern in summer over the North Pacific from 1960 to 2004, which has been attracting less attention than those in winter. The leading empirical orthogonal functions (EOFs) for August and September, which can be treated as the summer patterns, rather resemble each other in both spatial structure and time variations but are quite different from those of the other months. A lag correlation analysis indicates that the summer patterns do not show significant persistency in the following winter and the summer of the next year. An inappropriate definition of the summer season might obscure the characteristics of the dominant summer SST anomaly pattern in the North Pacific.  相似文献   

Effect of translate speed of typhoon on wind waves     

Inagaki  Naoto  Shibayama  Tomoya  Esteban  Miguel  Takabatake  Tomoyuki 《Natural Hazards》2021,105(1):841-858

Natural Hazards - Quantitative assessments on the effect of translate speed of typhoons on wind waves were carried out. A WRF-SWAN coupled model that used observed meteorological data was applied...  相似文献   

Atmospheric helium isotope ratio: Possible temporal and spatial variations     

Yuji Sano  Yukiko Furukawa  Naoto Takahata 《Geochimica et cosmochimica acta》2010,74(17):4893-4901

The atmospheric ³He/⁴He ratio has been considered to be constant on a global scale, because the residence time of helium is significantly longer than the mixing time in the atmosphere. However, this ratio may be decreasing with time owing to the anthropogenic release of crustal helium from oil and natural gas wells, although this observation has been disputed. Here, we present the ³He/⁴He ratios of old air trapped in historical slags in Japan and of modern surface air samples collected at various sites around the world, measured with a newly developed analytical system. In air helium extracted from metallurgical slag found at refineries in operation between AD 1603 and 1907 in Japan, we determined a mean ³He/⁴He ratio of (5106 ± 108) × 10^-5 R_HESJ (where R_HESJ is the ³He/⁴He ratio of the Helium Standard of Japan), which is consistent with the previously reported value of (5077 ± 59) × 10^-5 R_HESJ for historical slags in France and United Arab Emirates and about 4% higher than that of average modern air, (4901 ± 4) × 10^-5 R_HESJ. This result implies that the air ³He/⁴He ratio has decreased with time as expected by anthropogenic causes. Our modern surface air samples revealed that the ³He/⁴He ratio increases from north to south at a rate of (0.16 ± 0.08) × 10^-5 R_HESJ/degree of latitude, suggesting that the low ³He/⁴He ratio originates in high-latitude regions of the northern hemisphere, which is consistent with the fact that most fossil fuel is extracted and consumed in the northern hemisphere.  相似文献   

Kalman filter finite element method applied to dynamic ground motion     

Yusuke Kato  Mutsuto Kawahara  Naoto Koizumi 《国际地质力学数值与分析法杂志》2009,33(9):1135-1151

The purpose of this paper is to investigate the estimation of dynamic elastic behavior of the ground using the Kalman filter finite element method. In the present paper, as the state equation, the balance of stress equation, the strain–displacement equation and the stress–strain equation are used. For temporal discretization, the Newmark ¼ method is employed, and for the spatial discretization the Galerkin method is applied. The Kalman filter finite element method is a combination of the Kalman filter and the finite element method. The present method is adaptable to estimations not only in time but also in space, as we have confirmed by its application to the Futatsuishi quarry site. The input data are the measured velocity, acceleration, etc., which may include mechanical noise. It has been shown in numerical studies that the estimated velocity, acceleration, etc., at any other spatial and temporal point can be obtained by removing the noise included in the observation. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Tectonic setting of high-Mg andesite magmatism in the SW Japan arc: K–Ar chronology of the Setouchi volcanic belt     

Yoshiyuki Tatsumi  Naoto Ishikawa  Ken Anno  Kyoichi Ishizaka  Tetsumaru Itaya 《Geophysical Journal International》2001,144(3):625-631

  相似文献   

Electrokinetic phenomena associated with a water injection experiment at the Nojima fault on Awaji Island, Japan   总被引：2，自引：0，他引：2  

Hideki Murakami  Takeshi Hashimoto  Naoto Oshiman  Satoru Yamaguchi  Yoshimori Honkura  Norihiko Sumitomo 《Island Arc》2001,10(3-4):244-251

Abstract Self-potential variations were measured to estimate the magnitude of electrokinetic and hydrological parameters (zeta potential and permeability) of the Nojima Fault zone in Awaji, Japan. The study observed self-potential variations that seemed to be associated with water flow from the injection well to the fracture zone, which were induced by turning the injection on and off. Amplitudes of the variations were a few to 0.03 V across 320–450 m dipoles. These variations can be explained well with an electrokinetic model. The quantity k/ζ (permeability/zeta potential) is in the range 1.6 × 10⁻¹³− 5.4 × 10⁻¹³ m²/V. Permeability of the Nojima fault zone can be estimated as approximately 10⁻¹⁶–10⁻¹⁵ m² on the assumption that the zeta potential is in the range –0.01 to –0.001 V.  相似文献