Tidal currents influenced by topographic eddies in Uchiumi Bay     

Hidetaka Takeoka  Hajime Murao 《Journal of Oceanography》1993,49(5):491-501

In the current record taken in Uchuimi Bay during summer in 1990, we find anomalous features that the tidal currents during spring and neap tides are quite different in both speed and direction, and the transition between them takes place suddenly. Relation between the variation of tidal current and the observed internal tide is examined, but they are poorly correlated. By examining the direction and phase of the current, it is inferred that these anomalous features are caused by the influence of topographic eddies formed perioidically in Uchiumi Bay.  相似文献   

Time-series observation of dissolved inorganic carbon and nutrients in the northwestern North Pacific     

Hajime Kawakami  Makio C. Honda  Masahide Wakita  Shuichi Watanabe 《Journal of Oceanography》2007,63(6):967-982

Time-series measurements of dissolved inorganic carbon (DIC) and nutrient concentrations were conducted in the northwestern North Pacific from October 2002 to August 2004. Assuming that data obtained in different years represented time-series seasonal data for a single year, vertical distributions of DIC and nutrients showed large seasonal variabilities in the surface layer (∼100 m). Seasonal variabilities in normalized DIC (nDIC) and nitrate concentrations at the sea surface were estimated to be 81–113 μmol kg⁻¹ and 12.7–15.7 μmol kg⁻¹, respectively, in the Western Subarctic Gyre. The variability in nutrients between May and July was generally at least double that in other seasons. In the Western Subarctic Gyre, estimations based on statistical analyses revealed that seasonal new production was 39–61 gC m⁻² and tended to be higher in the southwestern regions or coastal regions. The seasonal new productions in the northwestern North Pacific were two or more times higher than in the North Pacific subtropical gyre and the northeastern North Pacific. It is likely that this difference is due to spatial variations in the concentrations of trace metals and the species of phytoplankton present. In addition, from estimations of surface pCO₂ it was verified that the Western Subarctic Gyre is a source of atmospheric CO₂ between February and May and a sink for CO₂ between July and October.  相似文献   

Precise Positioning of Ocean Bottom Seismometer by Using Acoustic Transponder and CTD   总被引：1，自引：0，他引：1  

Shiobara  Hajime  Nakanishi  Ayako  Shimamura  Hideki  Mjelde  Rolf  Kanazawa  Toshihiko  Berg  Eivind W. 《Marine Geophysical Researches》1997,19(3):199-209

We have obtained precise estimates of the position of Ocean Bottom Seismometers (OBS) on the sea bottom. Such estimates are usually uncertain due to their free falling deployment. This uncertainty is small enough, or is correctable, with OBS spacing of more than 10 km usually employed in crustal studies. But, for example, if the spacing is only 200 m for OBS reflection studies, estimates of the position with an accuracy of the order of 10 m or more is required.The determination was carried out with the slant range data, ship position data and a 1D acoustic velocity structure calculated from Conductivity–Temperature–Depth (CTD) data, if they are available. The slant range data were obtained by an acoustic transponder system designed for the sinker releasing of the OBS or travel time data of direct water wave arrivals by airgun shooting. The ship position data was obtained by a single GPS or DGPS. The method of calculation was similar to those used for earthquake hypocenter determination.The results indicate that the accuracy of determined OBS positions is enough for present OBS experiments, which becomes order of 1 m by using the DGPS and of less than 10 m by using the single GPS, if we measure the distance from several positions at the sea surface by using a transponder system which is not designed for the precise ranging. The geometry of calling positions is most important to determine the OBS position, even if we use the data with larger error, such as the direct water wave arrival data. The 1D acoustic velocity structure should be required for the correct depth of the OBS. Although it is rare that we use a CTD, even an empirical velocity structure works well.  相似文献   

The idea of nature in the east in comparison with the west     

Hajime Nakamura Dr. 《GeoJournal》1992,26(2):113-128

Conclusion — Contemporary Implications According to Buddhist philosophy, men constitute just one class of living beings. As such, they have no right to unlimited use of natural resources. Also men have no right to unlimited exploitation of animal and plant life, which forms part of Nature. Until recently, Westerners or moderns tended to think that men were quite separate and different from the natural world. This assumption is ungrounded and unreasonable. It has brought about devastation. Men incur retaliation by nature.In order to deal with the difficult situation that has come about, we must seek a solution that is both objective and subjective. On the objective side, we must discard the arrogance of supposing that men are entitled to exploit the natural world at their own will, without limit and regardless of the consequences. It is not appropriate to maintain the idea of conquering nature. Nature should be met with affection. In this connection, we emphasize that the world of nature should not be monopolized by a few countries. The whole natural world should be shared by all mankind. We cannot but feel angry at the small, limited number of countries which totally control the reserves of a limited energy supply, and which are extravagantly wasting what nature has entrusted to them. Just as individual egoism must be curtailed and placed under control, so national and ethnic egoism also should be restrained in the name of justice and respect for nature.On the subjective side, there is need for correction of the opinion of moderns that the progress of mankind consists in the unlimited satisfaction of human desire for material objects. Buddhism taught satisfaction with what is given to men. To know being satisfied was thought to be the way to spiritual happiness. The key to the relationship between man and the environment may very well lie in the control of our desires according to this concept of satisfaction. For that purpose our desire should be scaled to the possibilities of nature conceived as supporting human existence. Nature is not an entity to confront us as if it were quite different from us; it is something to embrace, as we might think it as that from which we cannot separate ourselves. Admitting the disinction between man and nature, we have to think how to live with the knowledge that nature is necessary to us.  相似文献   

Caii K line asymmetries in two well-observed solar flares of October 18, 1990     

C. Fang  E. Hiei  T. Okamoto 《Solar physics》1991,135(1):89-97

Two-dimensional evolutions of two flares of October 18, 1990 have been well observed in the Caii K line with a CCD camera at Norikura station of National Astronomical Observatory in Japan. There are two common characteristics for the flares: 3 - 5 min before the impulsive phase, the heating already begins at the footpoints of the flares, but no asymmetry in line emission has been detected. After the onset of the impulsive phase, Caii K line emission at the footpoints shows strong red asymmetry, with the maximum asymmetry occurring at the same time as the peak of the radio bursts. The maximum downward velocity is about 30 50 km s^–1. For flare 1, blue and red asymmetries were observed in two sides of the footpoint area. They developed and attained a maximum nearly at the same time and the inferred Doppler velocities are comparable (30 40 km s^–1). This implies that two mass jets started from a small region and ejected along a loop but in opposite directions with roughly equivalent momentum. A possible mechanism has been discussed.  相似文献   

Characterization of water quality variation in the Mekong River at Vientiane by frequent observations     

Toshiaki Iida  Somphone Inkhamseng  Koshi Yoshida  Hajime Tanji 《水文研究》2011,25(23):3590-3601

To better understand the variation of water quality in the Mekong River, sampling and measurement were scheduled twice a week for about 3 years at Vientiane, followed by basic statistical analysis of the observed data. The frequent measurement revealed detailed characteristics of the water quality variation, which had not been detected by monthly observation in the previous studies. The variation in total ionic content was considered to be governed by dilution of the amount of water. Increases in turbidity could be attributed to physical effects including surface soil erosion and bed material resuspension at the time of discharge increase. Nitrogen concentrations were stably low during the low flow period and abruptly increased in May. After the annual maximum in late May, the nitrate concentration steadily decreased regardless of the remarkable rise in the discharge from mid‐July, whereas the ammonium concentration remained at a similar level until October. It was considered that the first small discernable runoff after the long dry season flushed the accumulated nitrogen in the surface soil and mobilized the nitrogen in the riverbed. The variation in phosphorus concentrations was different from that in nitrogen concentrations. During the high flow period, continual dilutions at discharge peaks and occasional large additions of phosphorus by surface runoff were suggested. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Wave set-up in the storm surge along open coasts during Typhoon Anita     

Soo Youl Kim  Tomohiro Yasuda  Hajime Mase 《Coastal Engineering》2010

Wave set-up in storm surges is studied using a numerical model for coasts in Tosa Bay, Japan, open to the Pacific Ocean. Simulation models employing only atmospheric pressures and winds as external forces are unable to properly simulate open coast storm surge heights, such as those due to Typhoon Anita (1970). However, the present study shows that a numerical model incorporating wave-induced radiation stresses, as well as wind stresses and pressure gradients, is able to account for the open coast surge heights. There is a maximum contribution of 40% by the radiation stresses to the peak sea level rises. This study also evaluates the effects of the tides; including the tides improves the agreement between the predicted water surface elevations and the observations. The difference in predictions between one-way coupling from wave to surge models and two-way coupling of the surge and wave models is found to be small.  相似文献   

The role of crabs (Macrophthalmus japonicus) burrows on organic carbon cycle in estuarine tidal flat,Japan     

Sosuke Otani  Yasunori Kozuki  Ryoichi Yamanaka  Hiromitsu Sasaoka  Tetsu Ishiyama  Yoshihito Okitsu  Hajime Sakai  Yoji Fujiki 《Estuarine, Coastal and Shelf Science》2010,86(3):434-440

The objective of this study is to elucidate the burrow structure and to clarify the role of burrows in material cycle in the tidal flat. In our work, we focused on the dominant species in muddy tidal flat, crab Macrophthalmus japonicus.Burrow structure of Macrophthalmus japonicus was investigated on a Katsuura river tidal flat in Tokushima prefecture, Japan, using in situ resin casting. Sampling was conducted in August 2006, and a total of 48 burrow casts were obtained. Burrows consisted mainly of J-shaped structures (98%) while the rest belonged to U-shaped structures (2%). The maximum measured burrow volume was 120 cm³ and wall surface area was 224 cm², while maximum burrow length and depth were 23.2 cm and 16.5 cm, respectively. Burrow volume and surface area were strongly correlated with carapace width of M. japonicus. Investigation of the individual number of M. japonicus in 13 quadrats (50 × 50 × 20 cm) was conducted using 2 mm sieve. The number of M. japonicus was 15–31 ind./m². Using cohort analysis we estimated that surface area of burrows was 0.07–0.15 m²/m².CO₂ emission rate was measured at the surface sediment during the period from June to December 2008. Results varied from 13.8 ± 2.2 to 49.4 ± 3.2 mg CO₂/m²/h, and organic carbon decomposition was 3.8 ± 0.6–13.5 ± 0.9 mg C/m²/h. This leads the increase of organic carbon decomposition by 1.1 times, because of the expansion of the tidal flat surface area by burrowing activity. Organic carbon decomposition in burrow walls therefore contributed to organic matter decomposition in the tidal flat. These results indicated that in situ activities of Macrophthalmus japonicus significantly influence the material cycle and it is important to consider the existence of burrow in order to understand the fluxes of materials and to evaluate the purification function of the tidal flat.  相似文献   

Harmonization of international risk assessment protocol     

Toyofuku H 《Marine pollution bulletin》2006,53(10-12):579-590

For over centuries developments in food production and new food safety management systems in most developed countries have been perceived by many to be efficient in the prevention of food-borne disease. Nevertheless a number of problems remain dominant, one of these being the high level of food-borne microbiological disease which seems, for some pathogens, to have increased over the last decades. The development of an interdisciplinary approach with direct interaction between surveillance and risk analysis systems is described as a potential basis for improved prevention of food-borne disease. Quantitative microbiological risk assessment is a relatively new scientific approach, able to link data from food within the entire food chain and the various data on human disease to provide a clear estimation of risk. Today food safety is one of the WHOs top eleven priorities; the Organization calls for more systematic and aggressive steps to be taken to reduce significantly the risk of microbiological food-borne diseases. Dealing with this challenge is one of the major challenges for the 21st century in regard to food safety, implying a significant re-direction of food microbiology efforts in many parts of the world.  相似文献   

Alfvén polar oscillations of relativistic stars     

Hajime Sotani  Kostas D. Kokkotas 《Monthly notices of the Royal Astronomical Society》2009,395(2):1163-1172

We study polar Alfvén oscillations of relativistic stars endowed with a strong global poloidal dipole magnetic field. Here, we focus only on the axisymmetric oscillations which are studied by numerically evolving the two-dimensional perturbation equations. Our study shows that the spectrum of the polar Alfvén oscillations is discrete in contrast to the spectrum of axial Alfvén oscillations which is continuous. We also show that the typical fluid modes, such as the f and p modes, are not significantly affected by the presence of the strong magnetic field.  相似文献