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31.
Propagation of hydromagnetic disturbances in the solar corona and Moreton's wave phenomenon 总被引:2,自引:0,他引:2
Yutaka Uchida 《Solar physics》1968,4(1):30-44
Moreton's wave phenomenon, observed to propagate across the solar disk during certain solar flares, may be explained as the intersection line between an expanding coronal wavefront surface and the chromosphere: The propagation of a hydromagnetic disturbance in a spherically symmetric model corona with a radial magnetic field is studied in the WKB-approximation, and the propagation paths of wavepackets, the shape of the wavefronts expanding in time, and the variation of the direction of material oscillation along the paths are discussed for disturbances in hydromagnetic wave modes. It is shown that the wavefront expanding in fast-mode in the corona has a circular intersection line with the chromosphere, which sweeps on the solar surface with a velocity and a direction of material oscillation just favorable for explaining the observed features of the phenomenon. 相似文献
32.
33.
Seawater samples were collected in the North Pacific along 175°E during a cruise of the Northwest Pacific Carbon Cycle Study (NOPACCS) program in 1994. Many properties related to the carbonate system were analyzed. By using well-known ratios to correct for chemical changes in seawater, the CO2 concentration at a given depth was back calculated to its initial concentration at the time when the water left the surface in winter. We estimated sea-surface CO2 and titration alkalinity (TA) in present-day winter, from which we evaluated the degree of air-sea CO2 disequilibrium in winter was. Using a correction factor for air-sea CO2 disequilibrium in winter, we reconstructed sea-surface CO2 in pre-industrial times. The difference between the back-calculated initial CO2 and sea-surface CO2 in pre-industrial times should correspond to anthropgenic CO2 input. Although the mixing of different water masses may cause systematic error in the calculation, we found that the nonlinear effect induced by the mixing of different water masses was negligible in the upper layer of the North Pacific subtropical gyre along 175°E. The results of our improved method of assessing the distribution of anthropogenic CO2 in that region show marked differences from those obtained using the previous back-calculation method. 相似文献
34.
Yutaka Nagata Junichi Takeuchi Makoto Uchida Isamu Ishikura Yoshitaka Morikawa Takashi Koike 《Journal of Oceanography》1999,55(3):407-416
The Kuroshio flows very close to Cape Shionomisaki when it takes a straight path. The detailed observations of the Kuroshio were made both on board the R/V Seisui-maru of Mie University and on board the R/V Wakayama of the Wakayama Prefectural Fisheries Experimental Station on June 11–14, 1996. It was confirmed that the current zone of the Kuroshio touches the coast and bottom slope just off Cape Shionomiaki, and that the coastal water to the east of the cape was completely separated from that to the west. The relatively high sea level difference between Kushimoto and Uragami could be caused by this separation of the coastal waters when the Kuroshio takes a straight path. This flow is rather curious, as the geostrophic flow, which has a barotropic nature and touches the bottom, would be constrained to follow bottom contours due to the vorticity conservation law. The reason why the Kuroshio leaves the bottom slope to the east of Cape Shionomisaki is attributed to the high curvature of the bottom contours there: if the current were to follow the contours, the centrifugal term in the equation of motion would become large and comparablee to the Coriolis (or pressure gradient) term, and the geostrophic balance would be destroyed. This creates a current-shadow zone just to the east of the cape. As the reason why the current zone of the Kuroshio intrudes into the coastal region to the west of the cape, it is suggested that the Kii Bifurcation Current off the southwest coast of the Kii Peninsula, which is usually found when the Kuroshio takes the straight path, has the effect of drawing the Kuroshio water into the coastal region. The sea level difference between Kushimoto and Uragami is often used to monitor the flow pattern of the Kuroshio near the Kii Peninsula. It should be noted that Uragami is located in the current shadow zone, while Kushimoto lies in the region where the offshore Kuroshio water intrudes into the coastal region. The resulting large sea level difference indicates that the Kuroshio is flowing along the straight path. 相似文献
35.
Yutaka Yoshikawa 《Journal of Oceanography》2012,68(6):971-983
Numerical experiments were performed to investigate the effects of eddies generated in deep water formation processes on an abyssal circulation in a closed bowl-shaped basin. Two sets of experiments were performed. One set was eddy-restricted experiments in which only a volume-driven (upwelling-driven) circulation was simulated and the other set was eddy-permitted experiments in which both a volume-driven circulation and an eddy-driven circulation were simulated. In the two layer experiment where the lower layer water is formed, a mean along-slope current is formed in the lower layer for both the eddy-restricted and eddy-permitted experiments. The direction of the current was not unique in the eddy-restricted experiment, but it was cyclonic in the eddy-permitted experiment. In the three layer experiments where water of the intermediate layer is formed, the mean along-slope current in the lowest layer is negligibly small in the eddy-restricted experiment, while it is large and cyclonic in the eddy-permitted experiment. The driving forcings of the eddy-driven circulation are quantified in terms of eddy fluxes of relative vorticity (Reynolds stress) and layer thickness (bolus velocity). These terms increase as the volume of the newly formed water increases, but they do not change greatly with the slope height. The magnitude of these terms changes with the slope width, but the sum of these terms does not vary greatly. As a result, the intensity of the eddy-driven circulation depends primarily on the volume of newly formed water. These dependences of eddy fluxes were interpreted using downgradient diffusion of potential vorticity. 相似文献
36.
Aiko Furukawa Robin Spence Yutaka Ohta Emily So 《Bulletin of Earthquake Engineering》2010,8(2):451-479
Collapse of adobe buildings during an earthquakes with various earthquake intensities is analyzed using the 3-dimensional
distinct element method code developed by the first author. Firstly, we evaluate structural damage with damage index, interior-space
damage with w score, and human casualties in the collapsing buildings with three casualty criteria. Secondly, we investigate
relationships between the earthquake intensity, the structural damage, the interior-space damage, and the casualties. It is
found that the casualties have stronger correlation with the interior-space damage than the structural damage, and three vulnerability
functions, namely, structural, interior-space and casualty vulnerability functions, are proposed. Effects of reinforcing methods
on these functions are also examined. Finally, a series of analytical procedures to develop vulnerability functions and to
estimate casualties using the functions are described. 相似文献
37.
Anis Chekirbane Maki Tsujimura Atsushi Kawachi Hiroko Isoda Jamila Tarhouni Abdallah Benalaya 《水文科学杂志》2013,58(5):1097-1110
Abstract The Wadi Al Ayn plain is a coastal system on the eastern coast of Cap Bon in northeastern Tunisia. The area is known for its intensive agriculture, which is based mainly on groundwater exploitation. The aim of this study is to identify the sources of groundwater salinization in the Wadi Al Ayn aquifer system and deduce the processes that drive the mineralization. Surface water and groundwater samples were taken and analysed for major ions and stable isotopes. The geochemical data were used to characterize and classify the water samples based on a variety of ion plots and diagrams. Stable isotopes are useful tools to help us understand recharge processes and to differentiate between salinity origins. The oilfield brines infiltrated from the sandy bed of Wadi Al Ayn comprise the main source of groundwater salinization in the central part of the plain, while seawater intrusion is mainly responsible for the increased salinity in the groundwater of the coastal part of the plain (at Daroufa). Citation Chekirbane, A., Tsujimura, M., Kawachi, A., Isoda, H., Tarhouni, J., and Benalaya, A., 2013. Hydrogeochemistry and groundwater salinization in an ephemeral coastal flood plain: Cap Bon, Tunisia. Hydrological Sciences Journal, 58 (5), 1097–1110. 相似文献
38.
We investigated the plastics ingested by short-tailed shearwaters, Puffinus tenuirostris, that were accidentally caught during experimental fishing in the North Pacific Ocean in 2003 and 2005. The mean mass of plastics found in the stomach was 0.23 g per bird (n = 99). Plastic mass did not correlate with body weight. Total PCB (sum of 24 congeners) concentrations in the abdominal adipose tissue of 12 birds ranged from 45 to 529 ng/g-lipid. Although total PCBs or higher-chlorinated congeners, the mass of ingested plastic correlated positively with concentrations of lower-chlorinated congeners. The effects of toxic chemicals present in plastic debris on bird physiology should be investigated. 相似文献
39.
Itaru Yamashita Adichat Surinkum Yutaka Wada Makoto Fujihara Masao Yokoyama Haider Zaman Yo-ichiro Otofuji 《Journal of Asian Earth Sciences》2011,40(3):784-796
Jurassic to Cretaceous red sandstones were sampled at 33 sites from the Khlong Min and Lam Thap formations of the Trang Syncline (7.6°N, 99.6°E), the Peninsular Thailand. Rock magnetic experiments generally revealed hematite as a carrier of natural remanent magnetization. Stepwise thermal demagnetization isolates remanent components with unblocking temperatures of 620–690 °C. An easterly deflected declination (D = 31.1°, I = 12.2°, α95 = 13.9°, N = 9, in stratigraphic coordinates) is observed as pre-folding remanent magnetization from North Trang Syncline, whereas westerly deflected declination (D = 342.8°, I = 22.3°, α95 = 12.7°, N = 13 in geographic coordinates) appears in the post-folding remanent magnetization from West Trang Syncline. These observations suggest an occurrence of two opposite tectonic rotations in the Trang area, which as a part of Thai–Malay Peninsula received clockwise rotation after Jurassic together with Shan-Thai and Indochina blocks. Between the Late Cretaceous and Middle Miocene, this area as a part of southern Sundaland Block experienced up to 24.5° ± 11.5° counter-clockwise rotation with respect to South China Block. This post-Cretaceous tectonic rotation in Trang area is considered as a part of large scale counter-clockwise rotation experienced by the southern Sundaland Block (including the Peninsular Malaysia, Borneo and south Sulawesi areas) as a result of Australian Plate collision with southeast Asia. Within the framework of Sundaland Block, the northern boundary of counter-clockwise rotated zone lies between the Trang area and the Khorat Basin. 相似文献
40.