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排序方式: 共有217条查询结果,搜索用时 718 毫秒
171.
Koichi Ara Koh Yamaki Keisuke Wada Satoshi Fukuyama Takeshi Okutsu Sadao Nagasaka Akihiro Shiomoto Juro Hiromi 《Journal of Oceanography》2011,67(1):87-111
Seasonal and interannual variations in physicochemical properties (i.e., temperature, salinity, dissolved oxygen and dissolved
inorganic nutrients), chlorophyll a (Chl-a), particulate carbon and nitrogen (PC and PN, respectively), and primary production were investigated in the neritic area
of Sagami Bay, Kanagawa, Japan, from January 2002 to December 2008. These abiotic/biotic variables, except for NH4
+–N, repeated similar seasonal variations for all 7 years. On the basis of the analysis of data obtained on 167 sampling dates,
depth-integrated primary production in this water can be easily estimated from Chl-a at the surface using the regression equations obtained in the present study. Intermittently high values of dissolved inorganic
nutrients, Chl-a, PC, PN and primary productivity at the surface during the summer stratified period were induced by high freshwater discharge
from the rivers after rainfalls and by the expansion of nutrient-rich Tokyo Bay Water. Temperature, salinity and dissolved
inorganic nutrients showed drastic variations within a scale of a few days and/or weeks, and these variations were related
to sea levels that represent the intrusion of the Kuroshio Water, Intermediate Oyashio Water or deep water from the continental
slope. However, there was no consistent trend in the variations in Chl-a, PC, PN and primary production due to the complex effects of these waters. 相似文献
172.
From 1980 to 1995, in August, the bottom layer of Osaka Bay was occupied by cold, nutrient-rich water compared with that observed
during both previous and subsequent decades. To investigate the mechanisms for the intrusion of bottom-layer cold water into
Osaka Bay, the intrusion into Osaka Bay via the Kii Channel is simulated using a finite-volume coastal ocean model with unstructured
triangular cell grids. The initial conditions, boundary conditions, and surface temperature given to the model are obtained
from daily reanalysis data provided by the Japan Coastal Ocean Predictability Experiment. The model shows that cold water
uplifted on the eastern side of the Kii Peninsula is propagated westward at 1.0 m/s as a coastal boundary current; it reaches
the Kii Channel mouth when the Kuroshio axis is located around 74 km south of Cape Shionomisaki. However, the modeled cold
water mass at the Kii Channel mouth does not intrude further to the north of the Kii Channel; therefore, another mechanism
is required to explain the cold-water intrusion into the bottom layer of Osaka Bay. A plausible explanation is the estuarine
circulation established by the freshwater supply at the bay head. When the river runoff is included in the model without forced
vertical mixing, the temperature in Osaka Bay decreases 6.6 days later than the temperature decreases at the Kii Channel mouth.
Furthermore, the shoreward current speed in the bottom layer of the modeled estuarine circulation is 15 cm/s, which provides
the mechanism required for the cold water mass to pass the Kii Channel. 相似文献
173.
Glacial hazards in the Rolwaling valley of Nepal and numerical approach to predict potential outburst flood from glacial lake 总被引:3,自引:1,他引:2
Badri Bhakta Shrestha Hajime Nakagawa Kenji Kawaike Yasuyuki Baba Hao Zhang 《Landslides》2013,10(3):299-313
In recent years, climate change and retreating glaciers constitute a major hazard in the Himalaya of South Asia. Glacial lakes are rapidly developing or increasing due to climate change. The rapid development of the lake may cause outburst of the lake. The outburst discharge from the glacial lake can cause catastrophic flooding and disaster in downstream area. Therefore, it is necessary to investigate the impact of climate change on glacial lakes and to understand the characteristics of the glacial lake outburst. In this study, the field assessment of Tsho Rolpa Glacial Lake in the Himalaya of Nepal has been presented and the impact of climate change on this glacial lake has been discussed. The Tsho Rolpa Glacial Lake is the largest and most potentially dangerous glacial lake in Nepal. In addition, a numerical model has been also developed for computing the characteristics of glacial lake outburst due to moraine dam failure by seepage and water overtopping. The numerical model is tested for the flume experimental cases. The simulated results of the outburst discharge, the dam surface erosion, and the temporal variation of the moisture movement in the dam are compared with those obtained from the hydraulic model experiments. The moisture profile calculated by numerical model was agreeable with the experimental moisture profile. The simulated failure surface of the dam due to seepage by considering the suction in slope stability analysis gave more agreeable results than the Janbu's simplified method. The results of the outburst discharge and dam surface erosion also agreed with the experimental results. 相似文献
174.
175.
Woong-Seob Jeong Chris P. Pearson † Hyung Mok Lee Soojong Pak Takao Nakagawa 《Monthly notices of the Royal Astronomical Society》2006,369(1):281-294
We present a comprehensive analysis for the determination of the confusion levels for the current and the next generation of far-infrared surveys assuming three different cosmological evolutionary scenarios. We include an extensive model for diffuse emission from infrared cirrus in order to derive absolute sensitivity levels taking into account the source confusion noise due to point sources, the sky confusion noise due to the diffuse emission, and instrumental noise. We use our derived sensitivities to suggest best survey strategies for the current and the future far-infrared space missions Spitzer , AKARI ( ASTRO-F ), Herschel and SPICA . We discuss whether the theoretical estimates are realistic and the competing necessities of reliability and completeness. We find the best estimator for the representation of the source confusion and produce predictions for the source confusion using far-infrared source count models. From these confusion limits considering both source and sky confusions, we obtain the optimal, confusion limited redshift distribution for each mission. Finally, we predict the cosmic far-infrared background (CFIRB), which includes information about the number and distribution of the contributing sources. 相似文献
176.
Woong-Seob Jeong Hyung Mok Lee Soojong Pak Takao Nakagawa Suk Minn Kwon Chris P. Pearson Glenn J. White 《Monthly notices of the Royal Astronomical Society》2005,357(2):535-547
Fluctuations in the brightness of the background radiation can lead to confusion with real point sources. This type of confusion with background emission is relevant when making infrared (IR) observations with relatively large beam sizes, since the amount of fluctuation tends to increase with the angular scale. To quantitively assess the effect of the background emission on the detection of point sources for current and future far-IR observations by space-borne missions such as Spitzer , ASTRO-F , Herschel and Space Infrared Telescope for Cosmology and Astrophysics ( SPICA ), we have extended the Galactic emission map to a higher level of angular resolution than that of the currently available data. Using this high-resolution map, we estimate the sky confusion noise owing to the emission from interstellar dust clouds or cirrus, based on fluctuation analysis and detailed photometry over realistically simulated images. We find that the confusion noise derived by simple fluctuation analysis agrees well with the results from realistic simulations. Although sky confusion noise becomes dominant in long wavelength bands (>100 μm) with 60–90 cm aperture missions, it is expected to be two orders of magnitude lower for the next generation of space missions (with larger aperture sizes) such as Herschel and SPICA . 相似文献
177.
Tomoko Nakagawa 《Solar physics》1993,147(1):169-197
Planar magnetic structure (PMS) is an interplanetary magnetic structure in which magnetic field vectors are all parallel to a plane but highly variable in both magnitude and direction in that plane. This magnetic structure corresponds to re-entrant loops of magnetic field lines in the photosphere that emanate into interplanetary space. To find information on the generation site, occurrence properties of PMSs are investigated by using the interplanetary magnetic field data obtained by Sakigake and ISEE-3 spacecraft. No significant correlation is found between PMS occurrence and the solar wind velocity gradient which would suggest interplanetary formation of PMSs. No significant correlation is found between the PMS events and flares or filaments, either. Instead, a half of the PMSs were projected to the vicinity of the sector boundary in the source surface magnetic field, although there are exceptions when PMS appeared in the center of a sector. The PMS planes were not parallel to the current sheet at the sector boundary. Sometimes PMSs were observed recurrently at the same heliospheric longitude in successive rotations of the Sun, suggesting persistence of the source of PMS on the Sun. The orientation of the PMS planes were not conserved in the recurrent PMSs. 相似文献
178.
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