Synoptic-scale physical mechanisms associated with the Mei-yu front: A numerical case study in 1999     

Nguyen Minh Truong  Vu Thanh Hang  Roger A. Pielke Sr.  Christopher L. Castro  Koji Dairaku 《Asia-Pacific Journal of Atmospheric Sciences》2012,48(4):433-448

The Mei-yu front system occurring from 23 to 27 June 1999 consists of the Mei-yu front and the dewpoint front, which confine a warm core extending from the eastern flank of the Tibetan Plateau to the west of 145°E. To further understand the synopticscale physical mechanisms associated with the Mei-yu front system, the present study proposes another insight into the physical significance of the x-component relative vorticity (XRV) whose vertical circulation is expected to tilt isentropic surfaces. The XRV equation diagnoses exhibit that the twisting effect of the planetary vorticity (TEPV) is positive along the Mei-yu front and negative in the dewpoint front region, and tilts isentropic surfaces from south to north in the Mei-yu frontal zone. Conversely, the meridional gradient of the atmospheric buoyancy (MGAB) tilts isentropic surfaces in the opposite direction and maintains negative in the regions where the TEPV is positive and vice versa. Thus, the TEPV plays the role of the Mei-yu frontogenesis, whereas the MGAB demonstrates the Meiyu frontolysis factor. Both terms control the evolution of the cross-front circulation. The other terms show much minor contributions in this case study. The present simulations also indicate that the weakening of the upper-level jet evidently induces the weakening of the Mei-yu front and reduces the amplitude of the East Asia cold trough. Furthermore, the impact can also penetrate into the lower troposphere in terms of mesoscale disturbances and precipitation, proving that the upper-level jet imposes a noticeable top-down influence on the Mei-yu front system.  相似文献   

Geotechnical sealing material for coastal disposal facility for soils and wastes contaminated by radioactive cesium     

Takashi Tsuchida  Hiroki Murakami  Ooki Kurihara  A. M. R. G. Athapaththu  Yuichi Tanaka  Kazuhiko Ueno 《Marine Georesources & Geotechnology》2017,35(4):481-495

Safe disposal of wastes produced due to the process of decontamination in and around Fukushima No. 1 nuclear power plant is an urgent requirement. The purpose of this study was to develop a sealing material which can be used as an engineered barrier for a final disposal facility for the soils and wastes contaminated by radioactive cesium. The analyses conducted based on 4-m-thick sealing layer revealed that the hydraulic conductivity of the sealing material needs to be kept below 5.0?×?10^?10?m/s to avoid the seepage of contaminants below the environmentally safe limits. Sealing material was developed using marine clay–bentonite mixture and the engineering characteristics were examined. The results of laboratory experiments showed that, with the addition of bentonite, the hydraulic conductivity equal to or less than 5.0?×?10^?10?m/s was achieved when the effective consolidation stress is equal to or more than 27?kPa. From the tests for adsorption properties for cesium, it was found that the sealing material showed the significant capacity of adsorption for cesium in seawater. It was concluded that the construction of waste disposal facility on the sandy seafloor is feasible using the sealing layer proposed in this study.  相似文献   

Preferred orientation of the trace fossil Entradichnus meniscus in eolian dune strata (Djadokhta Formation) at Tugrikiin Shiree,southern Mongolia and its paleoecological implications     

Koji Seike  Hitoshi Hasegawa  Niiden Ichinnorov 《Island Arc》2010,19(4):622-627

Eolian sand dune deposits of the Upper Cretaceous Djadokhta Formation at Tugrikiin Shiree, southern Mongolia, yield not only dinosaur skeletal remains but also numerous trace fossils produced by invertebrates. This paper describes the trace fossil Entradichnus meniscus, a long unlined and unbranched trail that is filled with meniscate laminae and occurs characteristically in positive epirelief. The trail is straight to gently meandering, parallel to the foreset laminae of the eolian dunes, and exhibits a significant preferred orientation parallel to the depositional dip of the cross‐stratification laminae. In addition, almost all the crescentic internal laminae of the trail show concave down‐dips. These features indicate that the trails were produced beneath the slipface of eolian dunes by the downward burrowing of the trace‐makers. This occurrence mode of E. meniscus of the Mongolian Cretaceous is very similar to that described from the Jurassic eolian dune deposits in North America. Hence, the downward burrowing of the E. meniscus animal might be a common feature in arid eolian dune deposits at least during the Jurassic and Cretaceous, and possibly reflecting a behavioral response to the morphology of large sand dunes under an arid climate.  相似文献   

Distribution of boulders at Miyara Bay of Ishigaki Island,Japan: A flow characteristic indicator of tsunami and storm waves     

Kazuhisa Goto  Tetsuya Shinozaki  Koji Minoura  Kiyohiro Okada  Daisuke Sugawara  Fumihiko Imamura 《Island Arc》2010,19(3):412-426

This study investigates the distribution of boulders at Miyara Bay of Ishigaki Island, Japan. These boulders were deposited on a reef flat extending approximately 400–1300 m in width. Most boulders were rectangular to ellipsoidal, without sharp broken edges. They are reef and coral rock fragments estimated as <335 m³ (<633 t). Locally in the bay, the relationship between the boulder weight and position shows that boulders of a given weight have a clear limit on seaward distribution on the reef flat. For example, more than 1, 10, and 100 tons of boulders were deposited, respectively, more than 500, 300, and 100 m from the reef edge. The line is consistent with the possible landward transport limit by maximum storm waves at the Ryukyu Islands, suggesting that the line was formed by the reworking of some boulders by maximally strong storm waves, although we can not exclude the possibility that the line was formed by tsunamis. Furthermore, 68% of boulders at the bay are deposited beyond this line. Therefore, the presence of these boulders at their present positions is difficult to explain solely by storm waves, implying the possible tsunami origin of these boulders. The boulders are characteristically concentrated along the high‐tide line, suggesting the drastic reduction of the tsunami hydraulic force along the line. Previous studies using radiocarbon age dating, as well as our study, imply that at least 69 boulders at Miyara Bay were probably deposited at their present positions by the 1771 Meiwa tsunami, although some of these boulders might have been emplaced and displaced on the reef flat by prior tsunami or storm surges.  相似文献   

Distributions of the Venus 1.27-μm O₂ airglow and rotational temperature     

S. Ohtsuki  N. Iwagami  H. Sagawa  M. Ueno  Y. Kasaba  T. Imamura  K. Yanagisawa 《Planetary and Space Science》2008,56(10):1391-1398

Imaging spectroscopic observations of the Venus 1.27-μm O₂ airglow were carried out with ground-based telescopes from 2002 to 2007. Spectral image cubes were taken with the Okayama Astrophysical Observatory/infrared imaging spectrometer (superOASIS), the Gunma Astronomical Observatory/near-infrared camera and NASA's Infrared Telescope Facility/cryogenic echelle spectrograph (CSHELL). The rotational temperature shows weak positive correlation with the airglow intensity. However, there are some regions that have almost same intensities but different temperatures. The intensities tend to decrease from the anti-solar point to the terminator besides local features. These results indicate that there are local strong downward flows superimposed on the subsolar-to-antisolar circulation.  相似文献   

Hemispheric distributions of HCl above and below the Venus’ clouds by ground-based 1.7 μm spectroscopy     

N. Iwagami  S. Ohtsuki  K. Tokuda  N. Ohira  T. Imamura  H. Sagawa  G.L. Hashimoto  M. Ueno  S. Okumura 《Planetary and Space Science》2008,56(10):1424-1434

The abundance of hydrogen chloride (HCl) in the Venus atmosphere was measured by ground-based IR spectroscopy. The dayside measurements were performed in May 2007 with a resolution of 40,000, and the nightside measurements in October 1999 with a resolution of 1000. The hemispheric distributions of the HCl mixing ratio measured above the Venus’ clouds show no significant structure with a disc-averaged value of 0.74±0.06 ppm which is in the similar range as the previous report of 0.6±0.2 ppm. The representative height for the dayside measurements is estimated to be 60-66 km. Recent results by Venus Express/SPICAV/SOIR show much smaller values of 0.1-0.2 ppm at 64-94 km; however the direct comparison is difficult due to the different spatial conditions. The hemispheric distributions of the ³⁵Cl/³⁷Cl isotope ratio are also found to show no significant structure with a disc-averaged value of 3.1±0.4 which coincides with the terrestrial value of 3.1. The HCl mixing ratios below the clouds are also found to show no significant structure with a disc-averaged value of 0.40±0.05 ppm, which is similar to the previous reports of 0.4-0.5 ppm. The larger HCl mixing ratio above the clouds than below suggests the production of HCl in the cloud region or above. Also, a uniform hemispherical distribution of H₂O is found below the clouds with a disc-averaged mixing ratio of 25±5 ppm; this is in the same range as the previous measurements. Those uniform distributions of HCl and H₂O support the fact that their chemical lifetimes are much longer than that of mixing as has been discussed so far.  相似文献   

Rapid decrease of mass balance observed in the Xiao (Lesser) Dongkemadi Glacier,in the central Tibetan Plateau   总被引：1，自引：0，他引：1  

Jianchen Pu  Tandong Yao  Meixue Yang  Lide Tian  Ninlian Wang  Yutaka Ageta  Koji Fujita 《水文研究》2008,22(16):2953-2958

The mass balance of the Xiao (Lesser) Dongkemadi Glacier located in the Tanggula Mountains, of the central Qinghai‐Tibetan Plateau has been monitored since 1989. The results show that the mass balance of the glacier has recently shown a deficit trend, and that the glacial terminus was also retreating. Positive mass balance of the glacier was dominant during the period 1989–1993, and the accumulated mass balance reached 970 mm. However, negative mass balance of the glacier has occurred since 1994, except for the large positive mass balance year 1997. The mass balance was ? 701 mm in 1998, an extremely negative glacier mass balance year. The equilibrium line altitude showed a significant increasing trend. The mass balance of the glacier has changed from a significantly positive mass balance to a strongly negative mass balance since 1994. Meteorological data suggest that the rapid decrease in the mass balance is related to summer season warming. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Characterization of sulfate mineral deposits in central Thailand          下载免费PDF全文

Junichiro Kuroda  Hidetoshi Hara  Katsumi Ueno  Thasinee Charoentitirat  Teruyuki Maruoka  Takashi Miyazaki  Akira Miyahigashi  Stefano Lugli 《Island Arc》2017,26(2)

In this paper we present petrographic and geochemical data of sulfate mineral deposits in northeast Nakhon Sawan, central Thailand, and provide new constraints on their age. The deposits are made up mainly of strongly deformed nodular and massive gypsum in the upper part, and less deformed layered anhydrite in the lower part. They are intruded by andesitic dikes that contain Middle Triassic zircons (ca 240 Ma). These dikes are probably part of the regional magmatic activity of the Sukhothai Arc during the Early to Middle Triassic. Sulfur (δ³⁴S) and strontium (⁸⁷Sr/⁸⁶Sr) isotopic compositions of the sulfates range from 15.86 ‰ to 16.26 ‰ and from 0.70810 to 0.70817, respectively. Comparisons with the Phanerozoic seawater isotopic evolution curve indicate that those values are best explained by precipitation of the sulfates from Carboniferous seawater, in particular seawater of late Mississippian age (ca 326 Ma), and this would be consistent with previous studies of calcareous fossils in the limestones that crop out around this site. Our interpretation is that evaporitic gypsum was originally precipitated from hypersaline seawater on a shallow lagoon or shelf on the Khao Khwang Platform during the Serpukhovian, and that this gypsum changed to anhydrite during early burial. The anhydrite was then cut by andesitic dikes during the Middle Triassic, and more recently the upper part of which was rehydrated during exhumation to form secondary gypsum near the surface.  相似文献   

Characteristic of the vertical seismic waves associated with the 1995 Hyogo‐ken Nanbu (Kobe), Japan earthquake estimated from the failure of the Daikai Underground Station     

Koji Uenishi  Shunsuke Sakurai 《地震工程与结构动力学》2000,29(6):813-821

The dynamic behaviour of underground structures built by cut‐and‐cover methods is discussed. A simple model analysis shows that a column supporting the overburden at midspan (central column) can resonate upon incidence of an elastic wave of a specific frequency. The analytical results indicate that not only the size and material properties of the column, but also the static load acting on the column (overburden) is a decisive factor that influences the resonant frequency. Based on the results obtained by the analysis, the mechanism of the failure at the Daikai Underground Station in Kobe caused by the 1995 Hyogo‐ken Nanbu, Japan, earthquake is investigated. It is shown that the wave‐induced damage to underground structures can concentrate on the sections with specific overburden, and from the induced damage, it is possible to estimate the frequency characteristics of the associated seismic waves. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

Effects of alkali and alkaline-earth cations on the high-pressure sound velocities of aluminosilicate glasses     

Aoki  Koji  Sakamaki  Tatsuya  Ohashi  Tomonori  Ikeda  Osamu  Suzuki  Akio 《Physics and Chemistry of Minerals》2020,47(6):1-9

Physics and Chemistry of Minerals - A black tourmaline sample from Seagull batholith (Yukon Territory, Canada) was established to be a schorl with concentrations of Fe2+ among the highest currently...  相似文献