The dynamical evolution and star formation history of the Small Magellanic Cloud: effects of interactions with the Galaxy and the Large Magellanic Cloud     

Akira M. Yoshizawa  Masafumi Noguchi 《Monthly notices of the Royal Astronomical Society》2003,339(4):1135-1154

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Sea‐surface temperature and salinity changes in the northwest Pacific since the Last Glacial Maximum     

Tadamichi Oba  Masafumi Murayama 《第四纪科学杂志》2004,19(4):335-346

The oxygen isotope records of both benthic and planktonic Foraminifera in five piston cores, collected from the region between the Oyashio and Kuroshio Currents near Japan, clearly show the marked latitudinal shifts of these two currents during the past 25 kyr. Under the present hydrographic condition, a clear relationship between the sea‐surface temperature (SST) and oxygen isotope differences from benthic to planktonic Foraminifera is observed in this region. Using this relationship, we find decreased SSTs of 12–13°C (maximum 15°C) in the southernmost core site at the Last Glacial Maximum (LGM), indicating the Oyashio Current shifted southward. The SSTs at the southern two core sites abruptly increased more than 10°C at 10–11 ka, suggesting the Kuroshio Current shifted northward over these sites at 10–11 ka. In contrast, the northern two core sites have remained under the influence of the cold Oyashio Current for the past 25 kyr. With the reasonable estimate of bottom‐water temperature decrease of 2.5°C at the LGM, the SSTs estimated by this new method give exactly the same SST values calculated from Mg/Ca ratio of planktonic Foraminifera, allowing palaeosea‐surface salinities to be reconstructed. The result suggests that the ice volume effect was 1.0 ± 0.1‰ at the LGM. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

Non-hydrostatic Kelvin waves in the ocean     

Motoyasu Miyata 《Journal of Oceanography》1979,35(1):43-46

A theory of the coastal Kelvin wave is presented in which the pressure is assumed not to be hydrostatic. The results show that the non-hydrostatic Kelvin wave is dispersive and that the e^–1 decay distance of the wave amplitude from the coast decreases as the wave length becomes shorter. Similar conclusions can be drawn on the equatorial Kelvin wave.  相似文献   

The instability of viscous two-layer oscillatory flows     

Masafumi Kamachi  Hiroyuki Honji 《Journal of Oceanography》1983,38(6):346-356

The instability of oscillatory flows in a two-layer fluid where the two layers differ in density and viscosity has been analysed using a perturbation method for long waves with special interest on effects of viscosity, time scale, density and depth of the fluid. The flow of a fluid with homogeneous density can be unstable, when the kinematic viscosity of the upper fluid layer is different from that of the lower one. Viscosity stratification results in unstable oscillatory flows. Two limiting cases of single-layer flow are also considered.  相似文献   

Introduction to Special Section: Kuroshio Observation, State Estimation and Prediction     

Shiro Imawaki  Hiroshi Ichikawa  Motoyoshi Ikeda  Atsuhiko Isobe  Masafumi Kamachi 《Journal of Oceanography》2004,60(2):265-268

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A Reconstruction of Observed Profiles in the Sea East of Japan Using Vertical Coupled Temperature-Salinity EOF Modes   总被引：4，自引：0，他引：4  

Yosuke Fujii  Masafumi Kamachi 《Journal of Oceanography》2003,59(2):173-186

It is important to estimate hard-to-observe parameters in the ocean interior from easy-to-observe parameters. This study therefore demostrates a reconstruction of observed temperature and salinity profiles of the sea east of Japan (30°≈40°N, 140°≈150°E). The reconstruction was done by estimating suboptimal state from several values of the observed profiles and/or sea surface dynamic height (SDH) calculated from the profiles. The estimation used a variational method with vertical coupled temperature-salinity empirical orthogonal function (EOF) modes. Profiles of temperature and salinity in the subtropical region are effectively reconstructed from in situ temperature profile data, or sea surface temperature (SST) and SDH. For example, the analyzed temperature field from SST and SDH has an accuracy to within 1°C in the subtropical region. Salinity in the sea north of Kuroshio, however, is difficult to estimate because of its complex variability which is less correlated with temperature than in the subtropical region. Sea surface salinity is useful to estimate the subsurface structure. We also show the possibility that the estimation is improved by considering nonlinearity in the equation calculating SDH from temperature and salinity analysis values in order to examine the misfit between analysis and observation. Analysis using TOPEX/POSEIDON altimetry data instead of SDH was also performed. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Fully nonlinear numerical wave tank (NWT) simulations and wave run-up prediction around 3-D structures     

J. -C. Park  M. -H. Kim  H. Miyata  H. -H. Chun 《Ocean Engineering》2003,30(15):1969-1996

A finite-difference scheme and a modified marker-and-cell (MAC) algorithm have been developed to investigate the interactions of fully nonlinear waves with two- or three-dimensional structures of arbitrary shape. The Navier–Stokes (NS) and continuity equations are solved in the computational domain and the boundary values are updated at each time step by the finite-difference time-marching scheme in the framework of a rectangular coordinate system. The fully nonlinear kinematic free-surface condition is implemented by the marker-density function (MDF) technique developed for two fluid layers.To demonstrate the capability and accuracy of the present method, the numerical simulation of backstep flows with free-surface, and the numerical tests of the MDF technique with limit functions are conducted. The 3D program was then applied to nonlinear wave interactions with conical gravity platforms of circular and octagonal cross-sections. The numerical prediction of maximum wave run-up on arctic structures is compared with the prediction of the Shore Protection Manual (SPM) method and those of linear and second-order diffraction analyses based on potential theory and boundary element method (BEM). Through this comparison, the effects of non-linearity and viscosity on wave loading and run-up are discussed.  相似文献   

Evaluation of change in subsurface thermal environment due to groundwater flow in the Tokyo Lowland,Japan     

Akinobu Miyakoshi  Takeshi Hayashi  Atsunao Marui  Yasuo Sakura  Shinichi Kawashima  Masafumi Kawai 《International Journal of Earth Sciences》2008,97(2):401-411

Information on the distribution of subsurface temperature and hydraulic heads at 24 observation wells in and around the Tokyo Lowland, the eastern part of the Tokyo Metropolitan area, were examined to make clear the relationship between groundwater and the subsurface thermal environment in the urban area. Minimums in temperature–depth logs due to subsurface temperature increasing at shallow parts were recognized in 21 wells. This fact shows subsurface temperature is affected by ground surface warming in almost all of this area. Deeper than minimums, where the effects of surface warming became relatively small, regional variation is observed as follows: high temperatures are shown in the central part to the southern part, and low temperatures shown in the inland to eastern part. The high temperature area corresponds to an area where the lower boundary of groundwater flow is relatively shallow. This area corresponds also to an area with severe land subsidence resulting from excessive groundwater pumping. It is considered that this high temperature area is formed by the effects of upward groundwater flow affected by hydrogeological conditions and pumping. On the other hand, a comparison between past data (1956–1967) and present data (2001–2003) revealed widespread decreasing temperature in the inland area. This is explained by downward groundwater flow based on an analysis of temperature–depth logs. This fact suggests that subsurface temperature is not only increasing from the effects of surface warming but also decreasing from the effects of groundwater environment change due to pumping.  相似文献   

改进的切线性模式对一个边界层模式变分资料同化的改善   总被引：7，自引：0，他引：7  

Zhu Jiang  Wang Hui  Masafumi Kamachi 《大气科学进展》2002,19(4):563-582

大气、海洋中边界层物理过程的强非线性会对切线性模式近似（尤其是当积分时间长时）有较大的影响，从而给相应的4维变分资料同化问题的求解造成困难。本构造了Mellor-Yamada湍流封闭模式（level 2.5)的一个改进的切线性模式，相比通常的切线性模式和简化的切线性模式可以提高对非线性扰动的逼近。利用这个改进的切线性模式的伴随模式分别进行了1到7天的变分资料同化试验，得到了满意的结果。而用通常的伴随模式和简化的伴随模式都无法得到令人满意的结果。  相似文献   

K–Ar geochronology of the temporal change of eruptive style in the eastern Izu peninsula, central Japan     

Ayako  Ozawa  Takahiro  Tagami  Masafumi  Sudo 《Island Arc》2004,13(3):466-472

Abstract   A recent K–Ar study elucidated that eruptive style in the eastern Izu peninsula changed from polygenetic to monogenetic volcano at 0.3–0.2 Ma. To narrow down the time of change, we determined 10 K–Ar ages on Togasayama Andesite of Amagi volcano, the youngest polygenetic volcano in the area, and Togasayama Monogenetic Volcano, one of the oldest monogenetic volcanoes in the area, which overlies a part of the Togasayama Andesite. Dating results showed that the Togasayama Andesite effused at least from 0.34 to 0.20 Ma, whereas the Togasayama Monogenetic Volcano erupted at 0.26–0.29 Ma, suggesting that the northern part of the Togasayama Andesite effused after the eruption of the Togasayama Monogenetic Volcano. Considering previous data, it is therefore inferred that change of eruptive style in the eastern Izu area occurred during the period 0.29–0.20 Ma, with considerable overlap of both polygenetic and monogenetic volcanism.  相似文献