Wind-Tunnel and Numerical Simulations of the Coastal Thermal Internal Boundary Layer     

Tomohiro Hara  Yuji Ohya  Takanori Uchida  Ryohji Ohba 《Boundary-Layer Meteorology》2009,130(3):365-381

Wind-tunnel experiments in a thermally stratified wind tunnel and direct numerical simulations were performed to simulate the thermal internal boundary layer (TIBL) that developed over a coastal area in a sea-breeze flow. The results of the simulations were analyzed to investigate turbulence structure in the TIBL. To study the effects of the atmospheric stability over the sea on the TIBL, two vertical profiles of temperature were created in the upstream portion of the wind-tunnel experiment and the direct numerical simulation. Turbulence statistics of the TIBL changed significantly according to the temperature profile over the sea, indicating that the stability of the flow over the sea has a significant effect on the structure and turbulence characteristics of the TIBL. Furthermore, the TIBL heights were estimated from the vertical profiles of the local Richardson number. The estimated TIBL heights agreed with those predicted by a pre-existing relation, suggesting that both the wind-tunnel experiment and the direct numerical simulation accurately reproduced the growth of the TIBL.  相似文献   

Simple monitoring method for precaution of landslides watching tilting and water contents on slopes surface   总被引：2，自引：2，他引：0  

Taro Uchimura  Ikuo Towhata  Trinh Thi Lan Anh  Jou Fukuda  Carlos J. B. Bautista  Lin Wang  Ichiro Seko  Taro Uchida  Akira Matsuoka  Yosuke Ito  Yuichi Onda  Sho Iwagami  Min-Seok Kim  Naoki Sakai 《Landslides》2010,7(3):351-357

A low-cost and simple monitoring method for early warning of landslides is proposed. To detect abnormal deformation of a slope, this method employs a tilt sensor in place of an extensometer on the slope surface. In order to examine the relevance of measuring rotation angle on a slope surface by tilt sensor, model tests were conducted, and rotation on the slope surface was observed together with slide displacement along the surface. The rotation data responded 30 min before failure in a model test, which could be useful as a signal for early warning. However, the behavior of rotation before failure varies from case to case, and thus, criteria to issue warning should be defined more carefully. For a model slope made of uniform loose sand, measurement of slide displacement along the slope surface is sensitive to failure at the toe, while the measurement of rotation on the slope surface is useful to detect the development of progressive failure upward along the slope. Wireless sensor units with microelectromechanical systems (MEMS) tilt sensor and volumetric water content sensor were also examined on a real slope in Kobe City, and a long-term monitoring was attempted. A simple but possible way to define the criteria of judgment to issue warning can be proposed based on combination of data obtained by the tilt sensors and volumetric water content sensors.  相似文献   

EMECS8 – Harmonizing catchment and estuary     

Zhongyuan Chen  Tetsuo Yanagi  Eric Wolanski 《Estuarine, Coastal and Shelf Science》2010,86(3):v

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Phase transformations in the earth's mantle and subducting slabs: Implications for their compositions, seismic velocity and density structures and dynamics   总被引：3，自引：0，他引：3  

Tetsuo  Irifune 《Island Arc》1993,2(2):55-71

Abstract Phase transformations in model mantle compositions and those in subducting slabs have been reviewed to a depth of 800 km on the basis of recent high-pressure experimental data. Seismic velocity and density profiles in these compositions have also been calculated using these and other mineral physics data. The nature of the seismic velocity and density profiles calculated for a pyrolite composition was found to generally agree with those determined by seismic observations (e.g. PREM). The locations of the seismic discontinuities at 400 and 670 km correspond almost exactly to the depths where the transformations of the olivine component to denser phases take place. Moreover, the steep gradients in the seismic velocity/density profiles observed between these depths are qualitatively consistent with those expected from the successive transformations in the complementary pyroxene-garnet component in the pyrolite composition. Further, the calculated seismic velocity and density values agree well with those observed in the upper mantle and mantle transition region within the uncertainties attached to these calculations and observations. Pyrolite or peridotite compositions are thus most likely to represent the composition of the mantle above 670 km depth, although some degrees of chemical heterogeneity may exist in the transition region. The observed sharp discontinuous increases of seismic velocities and density at this depth may be attributed either to the phase transformation to a perovskite-bearing assemblage in pyrolite or to chemical composition changes. Density profiles in subducted slabs have been calculated along adequate geotherms assuming that the slabs are composed of the former oceanic crust underlain by a thicker harzburgitic layer. It is shown that the former oceanic crust is substantially less dense than the surrounding pyrolite mantle at depths below 670 km, while it is denser than pyrolite in the upper mantle and the transition region. The subducted former oceanic crust may be trapped in this region, forming a geochemically enriched layer at the upper mantle-lower mantle boundary. Thick and cool slabs may penetrate into the lower mantle, but the chemically derived buoyancy may result in strong deformation and formation of megalith structures around the 670 km seismic discontinuity. These structures are consistent with those detected by recent seismic tomography studies for subduction zones.  相似文献   

Melting of enstatite from 13 to 18 GPa under hydrous conditions     

Akihiro Yamada  Tetsuo Irifune 《Physics of the Earth and Planetary Interiors》2004,147(1):45-56

Experiments on MgSiO₃ enstatite were conducted in the pressure range from 13 to 18 GPa under hydrous conditions in order to clarify the effect of water on the melting phase relations of enstatite at pressures corresponding to the Earth’s mantle transition zone. In some previous experiments [Geol. Soc. Am. Bull. 79 (1968) 1685; Phys. Earth Planet. Inter. 85 (1994) 237], incongruent melting behavior to form Mg₂SiO₄ forsterite and SiO₂ enriched liquid up to 5 GPa was observed, and congruent melting behavior at pressures up to 12 GPa was observed. Under hydrous conditions, we found that the melting reaction changes from congruent to incongruent at around 13.5 GPa. Liquid formed above 13.5 GPa is enriched in MgO component relative to MgSiO₃ because it coexists with stishovite (SiO₂). Moreover, the solidus temperature decreases drastically at around 13.5 GPa, in unison with the change in the melting reaction. The solidus temperature is about 1400 °C at 13 GPa, but approximately 900 °C at 15 GPa. Our results show that the liquidus phase changes from clinoenstatite to stishovite with increasing pressure and water content above 13.5 GPa. MgSiO₃ enstatite is one of the major constituent minerals in the Earth’s mantle, and it is expected that MgO-enriched liquid will be generated in the transition zone if water is present.  相似文献   

Aircraft Observations of the Development of Thermal Internal Boundary Layers and Scaling of the Convective Boundary Layer Over Non-Homogeneous Land Surfaces   总被引：1，自引：0，他引：1  

Michail A. Strunin  Tetsuya Hiyama  Jun Asanuma  Tetsuo Ohata 《Boundary-Layer Meteorology》2004,111(3):491-522

This study investigates the convective boundary layer (CBL) that develops over anon-homogeneous surface under different thermal and dynamic conditions. Analysesare based on data obtained from a Russian research aircraft equipped with turbulentsensors during the GAME-Siberia experiment over Yakutsk in Siberia, from April to June 2000.Mesoscale thermal internal boundary layers (MTIBLs) that radically modified CBLdevelopment were observed under unstable atmospheric conditions. It was found thatMTIBLs strongly influenced the vertical and horizontal structures of virtual potentialtemperature, specific humidity and, most notably, the vertical sensible and latent heatfluxes. MTIBLs in the vicinity of the Lena River lowlands were confirmed by clouddistributions in satellite pictures.MTIBLs spread through the entire CBL and radically modify its structure if the CBL isunstable, and strong thermal features on the underlying surface have horizontal scalesexceeding 10 km. MTIBL detection is facilitated through the use of special parameterslinking shear stress and convective motion.The turbulent structure of the CBL with and without MTIBLs was scaled usingthe mosaic or flux aggregate approach. A non-dimensional parameterL_Rau/L_hetero (where L_Rau is Raupach's length and L_hetero is the horizontal scale of the surface heterogeneity)estimates the application limit of similarity and local similarity scaling models forthe mosaic parts over the surface. Normalized vertical profiles of wind speed, airtemperature, turbulent sensible and latent heat fluxes for the mosaic parts withL_RauL_hetero < 1 could be estimated by typical scalingcurves for the homogeneous CBL. Traditional similarity scaling models for the CBLcould not be applied for the mosaic parts with L_Rau/L_hetero > 1.For some horizontally non-homogeneous CBLs, horizontal sensible heat fluxes werecomparable with the vertical fluxes. The largest horizontal sensible heat fluxes occurred at the top of the surface layer and below the top of the CBL.Formerly affiliated to the Frontier Observational Research System for Global ChangeFormerly affiliated to the Frontier Observational Research System for Global Change  相似文献   

Electromagnetic fields in a steel-cased borehole   总被引：1，自引：0，他引：1  

Ki Ha Lee  Hee Joon Kim  Toshihiro Uchida 《Geophysical Prospecting》2005,53(1):13-21

The development of an electromagnetic numerical modelling scheme for a magnetic dipole in an arbitrary casing segment in an inhomogeneous conductivity background has been difficult, due to the very high electrical conductivity and magnetic permeability contrasts between the steel casing and the background medium. To investigate the effect of steel casing efficiently, we have developed an accurate but simple finite‐element modelling scheme to simulate electromagnetic fields in a medium of cylindrically symmetric conductivity structures. In order to preserve the cylindrical symmetry in the resulting electromagnetic fields, a horizontal loop current source is used throughout. One of the main advantages of the approach is that the problem is scalar when formulated using the azimuthal electric field, even if the casing is both electrically conductive and magnetically permeable. Field calculations have been made inside the cased borehole as well as in another borehole which is not cased. Careful analyses of the numerical modelling results indicate that the anomaly observed in a cross‐borehole configuration is sensitive enough to be used for tomographic imaging.  相似文献   

Stability and P–V–T equation of state of KAlSi3O8-hollandite determined by in situ X-ray observations and implications for dynamics of subducted continental crust material     

Norimasa Nishiyama  Robert Paul Rapp  Tetsuo Irifune  Takeshi Sanehira  Daisuke Yamazaki  Ken-ichi Funakoshi 《Physics and Chemistry of Minerals》2005,32(8-9):627-637

In situ X-ray diffraction measurements of KAlSi₃O₈-hollandite (K-hollandite) were performed at pressures of 15–27 GPa and temperatures of 300–1,800 K using a Kawai-type apparatus. Unit-cell volumes obtained at various pressure and temperature conditions in a series of measurements were fitted to the high-temperature Birch-Murnaghan equation of state and a complete set of thermoelastic parameters was obtained with an assumed K′_300,0=4. The determined parameters are V _300,0=237.6(2) Å³, K _300,0=183(3) GPa, (?K _T,0/?T) _P =?0.033(2) GPa K^?1, a ₀=3.32(5)×10^?5 K^?1, and b ₀=1.09(1)×10^?8 K^?2, where a ₀ and b ₀ are coefficients describing the zero-pressure thermal expansion: α _T,0 = a ₀ + b ₀ T. We observed broadening and splitting of diffraction peaks of K-hollandite at pressures of 20–23 GPa and temperatures of 300–1,000 K. We attribute this to the phase transitions from hollandite to hollandite II that is an unquenchable high-pressure phase recently found. We determined the phase boundary to be P (GPa)=16.6 + 0.007 T (K). Using the equation of state parameters of K-hollandite determined in the present study, we calculated a density profile of a hypothetical continental crust (HCC), which consists only of K-hollandite, majorite garnet, and stishovite with 1:1:1 ratio in volume. Density of HCC is higher than the surrounding mantle by about 0.2 g cm^?3 in the mantle transition zone while this relation is reversed below 660-km depth and HCC becomes less dense than the surrounding mantle by about 0.15 g cm^?3 in the uppermost lower mantle. Thus the 660-km seismic discontinuity can be a barrier to prevent the transportation of subducted continental crust materials to the lower mantle and the subducted continental crust may reside at the bottom of the mantle transition zone.  相似文献   

²³⁰Th/²³⁴U and ¹⁴C dating of a lowstand coral reef beneath the insular shelf off Irabu Island, Ryukyus, southwestern Japan     

Keiichi  Sasaki  Akio  Omura  Tetsuo  Miwa  Yoshihiro  Tsuji  Hiroki  Matsuda  Toru  Nakamori  Yasufumi  Iryu  Tsutomu  Yamada  Yuri  Sato  Hiroshi  Nakagawa 《Island Arc》2006,15(4):455-467

Abstract   High-resolution seismic reflection profiles delineated the distribution of mound-shaped reflections, which were interpreted as reefs, beneath the insular shelf western off Irabu Island, Ryukyus, southwestern Japan. A sediment core through one of the mounded structures was recovered from the sea floor at a depth of −118.2 m by offshore drilling and was dated by radiometric methods. The lithology and coral fauna of the core indicate that the mounded structure was composed of coral–algal boundstone suggesting a small-scaled coral reef. High-precision α-spectrometric ²³⁰Th/²³⁴U dating coupled with calibrated accelerator mass spectrometric ¹⁴C ages of corals obtained reliable ages of this reef ranging from 22.18 ± 0.63 to 30.47 ± 0.98 ka. This proves that such a submerged reef was formed during the lowstand stage of marine oxygen isotope stages 3–2. The existence of low-Mg calcite in the aragonitic coral skeleton of 22.18 ± 0.63 ka provides evidence that the reef had once been exposed by lowering of the relative sealevel to at least −126 m during the last glacial maximum in the study area. There is no room for doubt that a coral reef grew during the last glacial period on the shelf off Irabu Island of Ryukyus in the subtropical region of western Pacific.  相似文献   

The 10 ka multiple vent pyroclastic eruption sequence at Tongariro Volcanic Centre, Taupo Volcanic Zone, New Zealand: Part 2. Petrological insights into magma storage and transport during regional extension     

Mitsuhiro Nakagawa  Ian A Nairn  Tetsuo Kobayashi   《Journal of Volcanology and Geothermal Research》1998,86(1-4)

The six eruption episodes of the 10 ka Pahoka–Mangamate (PM) sequence (see companion paper) occurred over a ?200–400-year period from a 15-km-long zone of multiple vents within the Tongariro Volcanic Centre (TgVC), located at the southern end of the Taupo Volcanic Zone (TVZ). Most TgVC eruptives are plagioclase-dominant pyroxene andesites and dacites, with strongly porphyritic textures indicating their derivation from magmas that ascended slowly and stagnated at shallow depths. In contrast, the PM pyroclastic eruptives show petrographic features (presence of phenocrystic and groundmass hornblende, and the coexistence of olivine and augite without plagioclase during crystallisation of phenocrysts and microphenocrysts) which suggest that their crystallisation occurred at depth. Depths exceeding 8 km are indicated for the dacitic magmas, and >20 km for the andesitic and basaltic andesitic magmas. Other petrographic features (aphyric nature, lack of reaction rims around hornblende, and the common occurrence of skeletal microphenocrystic to groundmass olivine in the andesites and basaltic andesites) suggest the PM magmas ascended rapidly immediately prior to their eruption, without any significant stagnation at shallow depths in the crust. The PM eruptives show three distinct linear trends in many oxide–oxide diagrams, suggesting geochemical division of the six episodes into three chronologically-sequential groups, early, middle and late. Disequilibrium features on a variety of scales (banded pumice, heterogeneous glassy matrix and presence of reversely zoned phenocrysts) suggest that each group contains the mixing products of two end-member magmas. Both of these end-member magmas are clearly different in each of the three groups, showing that the PM magma system was completely renewed at least three times during the eruption sequence. Minor compositional diversity within the eruptives of each group also allows the PM magmas to be distinguished in terms of their source vents. Because petrography suggests that the PM magmas did not stagnate at shallow levels during their ascent, the minor diversity in magmas from different vents indicates that magmas ascended from depth through separate conduits/dikes to erupt at different vents either simultaneously or sequentially. These unique modes of magma transport and eruption support the inferred simultaneous or sequential tapping of small separate magma bodies by regional rifting in the southern Taupo Volcanic Zone during the PM eruption sequence (see companion paper).  相似文献