Numerical experiments on wind-driven circulations and associated transport processes in Suruga Bay     

Kiyoshi Tanaka  Yutaka Michida  Teruhisa Komatsu 《Journal of Oceanography》2008,64(1):93-102

The dynamics of the wind-driven circulations and surface transport processes in Suruga Bay have been examined by performing numerical experiments. While strong winds exist outside the bay, the winds inside the bays are greatly reduced, which generates a strong wind stress curl in winter and autumn. In particular, in winter, a strong positive curl region is located across the bay mouth, and a strong surface circulation with counterclockwise rotation is generated beneath it. The circulation is nearly geostrophic, but is not affected by the bottom topography in the deep bay. It is suggested that intense surface water exchange through the bay mouth occurs in winter, whereas it is not active in the other seasons when no significant vorticity is supplied on the bay mouth from the atmosphere. Moreover, we propose a hypothesis that the atmospheric wind stress curl will cause the frequent appearance of the counterclockwise circulation in winter in the real ocean.  相似文献   

Identification of the source caldera for the Middle Miocene ash-flow tuffs in the Kii Peninsula based on apatite trace-element composition     

Reishi Takashima  Hiroyuki Hoshi  Yutaka Wada  Hironao Shinjoe 《Island Arc》2021,30(1):e12404

A large caldera cluster consisting of at least four calderas (Omine, Odai, Kumano-North and Kumano calderas) existed in the central–southern part of the Kii Peninsula approximately 14–15 Ma. On the other hand, thick Middle Miocene ash-flow tuffs, referred to as the Muro Ash-flow Tuff and the Sekibutsu Tuff Member, are distributed in the northern part of the Kii Peninsula. Although these tuffs are considered to have erupted from the caldera cluster in the central-southern Kii Peninsula, identifying the source caldera in the cluster has been controversial because of similarities in the petrological characteristics and identical radiometric ages of the volcaniclastic rocks of these calderas. We successfully discriminated the characteristics of the eruptive products of each caldera in the caldera cluster based on the apatite trace-element compositions of the pyroclastic dikes and ash-flow tuffs of the calderas. We also demonstrated that the source caldera of at least the lower main part of the Muro Ash-flow Tuff and the Sekibutsu Tuff Member was the Odai Caldera, which is located in the central Kii Peninsula. Our findings show possible correlations among the pyroclastic conduits and ash-flow tuffs of the caldera-fill and/or outflow deposits, even in cases where they have been densely welded and diagenetically altered. This method is useful for the study of deeply eroded ancient calderas.  相似文献   

Non-stochastic colonization by pioneer plants after deglaciation in a polar oasis of the Canadian High Arctic     

Akira S. Mori  Masaki Uchida  Hiroshi Kanda 《Polar Science》2013,7(3-4):278-287

Initial plant colonization is critical in determining subsequent ecosystem development. In a High-Arctic oasis showing atypical “directional primary succession”, we quantified the microhabitat characteristics associated with colonization by pioneer vascular plants of a bare moraine. The study moraine, formed during the Little Ice Age, is located within the proglacial area at the southern front of Arklio Glacier, Ellesmere Island, Canada. We established two line-transects on this moraine to quantify microhabitats for vascular species. Microsites favorable for plants were concave depressions, probably increasing the likelihood of colonization. At microsites distant from stable boulders, which probably protect seeds/seedlings from wind desiccation, plant colonization was less likely. Furthermore, favorable microhabitat properties differed depending on topographical location within the moraine, suggesting that, even within a single moraine, microhabitats favorable for plant colonization are heterogeneously-distributed. This moraine was characterized by two major pioneer species, Epilobium latifolium and Salix arctica. Their species-specific microhabitat requirements highlight the importance of biotic factors in colonization processes. Favorable sites for plants are generally distributed at random in harsh environments. However, we showed that initial plant colonization is a deterministic process rather than random, indicating the possibility of non-stochastic processes even during the early phase of ecosystem development in High-Arctic ecosystems.  相似文献   

X-ray CT based numerical analysis of fracture flow for core samples under various confining pressures   总被引：1，自引：0，他引：1  

Noriaki Watanabe  Takuya Ishibashi  Yutaka Ohsaki  Yoshihiro Tsuchiya  Tetsuya Tamagawa  Nobuo Hirano  Hiroshi Okabe  Noriyoshi Tsuchiya 《Engineering Geology》2011,(4):338

The X-ray CT based numerical analysis of fracture flow for core samples, recently developed by the authors, was applied to two granite core samples having either a mated artificial or a mated natural fracture at confining pressures of 5 to 50 MPa. A third-generation medical X-ray CT scanner was used to image the samples within a core holder consisting of an aluminum liner and a carbon fiber overwrap. Fracture models (i.e., aperture distributions) were obtained by the CT images, the resolution of which was coarser than the apertures, and a single-phase flow simulation was performed using a local cubic law-based fracture flow model. Numerical results were evaluated by a fracture porosity measurement and a solution displacement experiment using NaCl and NaI aqueous solutions. These numerical results coincided only qualitatively with the experimental results, primarily due to image noise from the aluminum liner of the core holder. Nevertheless, the numerical results revealed flow paths within the fractures and their changes with confining pressure, whereas the experimental results did not provide such results. Different stress-dependencies in the flow paths were observed between the two samples despite the similar stress-dependency in fracture porosity and permeability. The changes in total area of the flow paths with confining pressure coincided qualitatively with changes in breakthrough points in the solution displacement experiment. Although the data is limited, the results of the present study suggest the importance of analyzing fluid flows within naturally fractured core samples under in situ conditions in order to better understand the fracture flow characteristics in a specific field. As demonstrated herein, X-ray CT-based numerical analysis is effective for addressing this concern. Using a multi-phase flow model, as well as a core holder constructed of an engineered plastic, should provide a useful, non-destructive, and non-contaminative X-ray CT-based fracture flow analysis for core samples under in situ conditions in future studies.  相似文献   

Magmatic diversity of western Mexico as a function of metamorphic transformations in the subducted oceanic plate   总被引：1，自引：0，他引：1  

Arturo Gómez-Tuena  Laura Mori  Ofelia Pérez-Arvizu 《Geochimica et cosmochimica acta》2011,75(1):213-241

This geochemical study of the Mexican subduction zone elucidates how metamorphic and dehydration reactions affecting the subducted oceanic plate at different depths can influence magmatic diversity. In the western Trans-Mexican Volcanic Belt, there is a narrow potassic volcanic front running in parallel to the Middle American Trench that becomes replaced by intraplate-like high-Nb rocks to the north, and by more typical calc-alkaline products to the southeast. Potassic rocks have high MgO and are enriched in incompatible trace elements, but have lower heavy rare earth element contents than more evolved calc-alkaline and high-Nb magmas, and slightly more enriched Sr, Nd and Pb isotopes. Potassic magmas also have higher Rb/Cs and Ba/Cs ratios than the calc-alkaline and high-Nb suites, and extend to unusually high Nb/Ta ratios that correlate positively with Rb/Ta, Zr/Ta, La/Ta and Gd/Yb. These chemical variations are inconsistent with different extents of melting of a peridotitic source, but are also incompatible with melting of a phlogopite-rich mantle (vein-plus-wall-rock relationship), unless mica is totally consumed during melting, and a titaniferous phase such as rutile remains in the residue together with garnet. This assemblage is unlikely in the source region of primitive hydrous magmas, but it is what would be expected during dissolution of phengite and monazite/allanite in the subducted slab, with the concurrent formation of an anhydrous rutile-bearing eclogite. The magmatic diversity of western Mexico can thus be explained by invoking contributions of chemically different subduction agents as a function of slab depth and residual mineralogy: a low-pressure/temperature aqueous fluid would induce melting of the peridotitic mantle wedge and form typical calc-alkaline volcanoes, whereas a deeper and hotter slab-derived melt (or supercritical liquid) would contribute to the formation of potassic magmas due to phengite/monazite/allanite disintegration. In this context, intraplate-like magmas derive from decompression melting of the upper mantle as a natural consequence of subduction geodynamics.  相似文献   

Application of chemical tracers to an estimate of benthic denitrification in the Okhotsk Sea     

Masanori Ito  Yutaka W. Watanabe  Masahito Shigemitsu  Shinichi S. Tanaka  Jun Nishioka 《Journal of Oceanography》2014,70(5):415-424

To estimate benthic denitrification in a marginal sea, we assessed the usefulness of \({\text{N}}_{2}^{*}\) , a new tracer to measure the excess nitrogen gas (N₂) using dissolved N₂ and argon (Ar) with N* in the intermediate layer (26.6–27.4σ _θ ) of the Okhotsk Sea. The examined parameters capable of affecting \({\text{N}}_{2}^{*}\) are denitrification, air injection and rapid cooling. We investigated the relative proportions of these effects on \({\text{N}}_{2}^{*}\) using multiple linear regression analysis. The best model included two examined parameters of denitrification and air injection based on the Akaike information criterion as a measure of the model fit to data. More than 80 % of \({\text{N}}_{2}^{*}\) was derived from the denitrification, followed by air injection. Denitrification over the Okhotsk Sea shelf region was estimated to be 5.6 ± 2.4 μmol kg^?1. The distribution of \({\text{N}}_{2}^{*}\) was correlated with potential temperature (θ) between 26.6 and 27.4σ _θ (r = ?0.55). Therefore, we concluded that \({\text{N}}_{2}^{*}\) and N* can act complementarily as a quasi-conservative tracer of benthic denitrification in the Okhotsk Sea. Our findings suggest that \({\text{N}}_{2}^{*}\) in combination with N* is a useful chemical tracer to estimate benthic denitrification in a marginal sea.  相似文献   

Long-term (36-year) observations on the dynamics of the fish-killing raphidophyte Chattonella in Harima-Nada,eastern Seto Inland Sea,Japan     

Tetsuya Nishikawa  Yutaka Hori  Satoshi Nagai  Kazutaka Miyahara  Yukinobu Nakamura  Kazuhiro Harada  Kuninao Tada  Ichiro Imai 《Journal of Oceanography》2014,70(2):153-164

Long-term changes of the fish-killing raphidophyte Chattonella spp. (Chattonella antiqua, Chattonella marina and Chattonella ovata) were examined in relation to environmental factors at 19 sampling stations in Harima-Nada, eastern Seto Inland Sea, Japan, for 36 years from 1973 to 2008. Long-term trends in the dynamics of Chattonella populations were considered to relate to environmental factors such as nutrient concentrations and water temperature. High nutrient levels during the period from the 1970s to the early 1980s have contributed to the high cell density and large-scale red tides of Chattonella spp. in Harima-Nada. However, nutrient levels exhibited a decreasing trend thereafter, and it is thought that Chattonella spp. cannot form large-scale blooms under the present conditions. After the mid-1990s, the occurrence period of vegetative cells of Chattonella spp. has been several weeks or 1 month earlier than that of the 1970s and early 1980s, and the appearance frequency of Chattonella spp. has increased in the northern coastal area, although the cell density and the spatial scale of the distribution have become lower and smaller than those in the previous decades. It is suggested that the timing of germination of Chattonella cysts has become earlier as a result of the increase in water temperature, and the chances of vegetative growth have also increased, especially at the northern coast where most of large rivers discharge into the Harima-Nada. In addition, the present results revealed that fewer diatoms were also one of the significant factors for the high abundance of Chattonella spp. in Harima-Nada.  相似文献   

A multidimensional horizontal-loop controlled-source electromagnetic inversion method and its use to characterize heterogeneity in aquiferous fractured crystalline rocks   总被引：1，自引：0，他引：1  

Yutaka Sasaki  Max A. Meju 《Geophysical Journal International》2006,166(1):59-66

  相似文献   

Soft X-ray observation of a large-scale coronal wave and its exciter     

Hudson  Hugh S.  Khan  Josef I.  Lemen  James R.  Nitta  Nariaki V.  Uchida  Yutaka 《Solar physics》2003,212(1):121-149

Recent extreme ultraviolet (EUV) observations from SOHO have shown the common occurrence of flare-associated global coronal waves strongly correlated with metric type II bursts, and in some cases with chromospheric Moreton waves. Until now, however, few direct soft X-ray detections of related global coronal waves have been reported. We have studied Yohkoh Soft X-ray Telescope (SXT) imaging observations to understand this apparent discrepancy, and describe the problems in this paper. We have found good X-ray evidence for a large-scale coronal wave associated with a major flare on 6 May 1998. The earliest direct trace of the wave motion on 6 May consisted of an expanding volume within 20 Mm (projected) of the flare-core loops, as established by loop motions and a dimming signature. Wavefront analyses of the soft X-ray observations point to this region as the source of the wave, which began at the time of an early hard X-ray spike in the impulsive phase of the flare. The emission can be seen out to a large radial distance (some 220 Mm from the flare core) by SXT, and a similar structure at a still greater distance by EIT (the Extreme Ultraviolet Imaging Telescope) on SOHO. The radio dynamic spectra confirm that an associated disturbance started at a relatively high density, consistent with the X-ray observations, prior to the metric type II burst emission onset. The wavefront tilted away from the vertical as expected from refraction if the Alfvén speed increases with height in the corona. From the X-ray observations we estimate that the electron temperature in the wave, at a distance of 120 Mm from the flare core, was on the order of 2–4 MK, consistent with a Mach number in the range 1.1–1.3. Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1022904125479 deceased  相似文献   

3D Structure of Arcade-Type Flares Derived from the Homologous Flare Series of 21, 24, and 27 February 1992     

Morita  Satoshi  Uchida  Yutaka  Hirose  Shigenobu  Uemura  Shuhei  Yamaguchi  Tomotaka 《Solar physics》2001,200(1-2):137-156

In February 1992, three flares, which we consider constitute a homologous flare series (flares having basically the same configuration repeating in the same situation), occurred in the active region NOAA 7070 and were observed by Yohkoh SXT. In the present paper, we first discuss the homology of these three flares, and derive the 3D structure by making use of the information obtained from the three different lines of sight at common phases. The result of this analysis made clear for the first time that the so-called `cusped arcade' at the maximum phase in the well-known 21 February 1992 flare is, contrary to the general belief, an `elongated arch' created at the beginning of the flare, seen with a shallow oblique angle. It is not the `flare arcade' seen on axis as widely conceived. This elongated arch roughly coincides with a diagonal of the main body of the soft X-ray arcade that came up later. The magnetic structure responsible for the flare as a whole turned out to be a structure with quadruple magnetic sources – with the third and fourth sources also playing essential roles. The observationally derived information in our paper provides strong restrictions to the theoretical models of the process occurring in arcade flares.  相似文献