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21.
Kazuhiro?AokiEmail author Manabu?Shimizu Hiroshi?Kuroda Toshifumi?Yamatogi Naoya?Ishida Shigeru?Kitahara Keiji?Hirano 《Journal of Oceanography》2016,72(5):811-816
In both 2009 and 2010, massive Chattonella blooms occurred in Tachibana Bay. Observation results show that high cell densities of Chattonella were distributed in the central area of Tachibana Bay with low salinity water. Model results indicate that the low salinity water originated from the Ariake Sea and intruded into Tachibana Bay during the northerly or weak winds. It is suggested that low salinity water was mainly discharged from the northern area of the Ariake Sea. Northerly wind enhanced the horizontal advection of the low salinity water intruding into Tachibana Bay originating from the northern area of the Ariake Sea. 相似文献
22.
Akio Ishida Kisaburo Nakata Shigeaki Aoki Hiroshi Kutsukake Michio J. Kishi Masahisa Kubota 《Journal of Oceanography》2001,57(4):433-450
Distributions and characteristics of water mass and chlorofluorocarbons (CFCs) in the North Pacific are investigated by using
a General Circulation Model (GCM). The anthropogenic CO2 uptake by the ocean is estimated with velocity fields derived from the GCM experiments. The sensitivity of the uptake to
different diffusion parameterizations and different surface forcing used in the GCM is investigated by conducting the three
GCM experiments; the diffusive processes are parameterized by horizontal and vertical eddy diffusion which is used in many
previous models (RUN1), parameterized by isopycnal diffusion (RUN2), and isopycnal diffusion and perpetual winter forcing
for surface temperature and salinity (RUN3). Realistic features for water masses and CFCs can be simulated by the isopycnal
diffusion models. The horizontal and vertical diffusion model fails to simulate the salinity minimum and realistic penetration
of CFCs into the ocean. The depth of the salinity minimum layer is better simulated under the winter forcing. The results
suggest that both isopycnal parameterization and winter forcing are crucial for the model water masses and CFCs simulations.
The oceanic uptake of anthropogenic CO2 in RUN3 is about 19.8 GtC in 1990, which is larger by about 10% than that in RUN1 with horizontal and vertical diffusive
parameterization. RUN3 well simulates the realistic water mass structure of the intermediate layer considered as a candidate
of oceanic sink for anthropogenic CO2. The results suggest that the previous models with horizontal and vertical diffusive parameterization may give the oceanic
uptake of anthropogenic CO2 underestimated.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
23.
Yutaka?W.?WatanabeEmail author Hiroshi?Ishida Toshiya?Nakano Naoki?Nagai 《Journal of Oceanography》2005,61(6):1011-1016
Using time series of hydrographic data in the wintertime and summertime obtained along 137°E from 1971 to 2000, we found that
the average contents of nutrients in the surface mixed layer showed linear decreasing trends of 0.001∼0.004 μmol-PO4 l−1 yr−1 and 0.01∼0.04 μmol-NO3 l−1 yr−1 with the decrease of density. The water column Chl-a (CHL) and the net community production (NCP) had also declined by 0.27∼0.48
mg-Chl m−2 yr−1 and 0.08∼0.47 g-C-NCP m−2 yr−1 with a clear oscillation of 20.8±0.8 years. These changes showed a strong negative correlation with the Pacific Decadal Oscillation
Index (PDO) with a time lag of 2 years (R = 0.89 ± 0.02). Considering the recent significant decrease of O2 over the North Pacific subsurface water, these findings suggest that the long-term decreasing trend of surface-deep water
mixing has caused the decrease of marine biological activity in the surface mixed layer with a bidecadal oscillation over
the western North Pacific. 相似文献
24.
A statistical study of 228 flares on the three UV Ceti-type stars, i.e., YZ CMi, AD Leo, and EV Lac, is presented. Observations were gathered by Ichimura and Shimizu over a total monitoring time of 907 hours distributed over 18 years (1971 to 1988). Period analysis of flare activity was performed, and no periodicity was detected on the three stars for either the flare number rate or the energy rate in time-scales ranging from a year up to 14 years. Average colour of flares at peak was (U-B)=–0.98±0.17 and (B-V)=0.05±0.13. Cumulative number distributions of flare event time-integrated energies were solved by a least-squares method on a log-log plot for a power-law function to get both the constant of and the gradient , which were found to be similar among the three stars. The gradient showed that rare large flare events radiate most of the energy released by all the flare events in the monitoring time. The flare number rate and energy rate are similar if the power-law distributions are extended up to a specific maximum energy. In reality, the Kolmogorov-Smirnov test showed that the observed cumulative number distributions of flare event energy were not necessarily a power-law function. The monte-Carlo simulation, however, indicates that the monitoring time and/or the patrol observation time interval may not be long enough to get the average flare number rate and energy rate, especially at the upper energy limits which are statistically unreliable. 相似文献
25.
Summary Surface air temperature in central Japan was predicted from the temperature recordings from sensors in the Automated Meteorological Data Acquisition System (AMeDAS), using seven different procedures: the usual simple and universal kriging and cokriging estimators, the traditional regression analysis and the inverse distance weighted method. The cokriging estimator integrated digital elevation data as well as the air temperature readings. The performance of the procedures was evaluated and compared using cross-validation.The kriging estimator provided a better estimate than the traditional regression analysis that treated the data as spatially independent observations. The kriging estimate was also better than the inverse distance weighted method. Further improvement in the estimation accuracy was achieved by using cokriging procedures because of high correlation of air temperature with elevation. The accuracy of spatial prediction decreased due to nocturnal cooling in winter and daytime heating in summer. This decrease implies that a strong radiation balance at the surface, whether positive or negative, causes a relatively short-range variation in surface air temperature through the effects of local environments.With 8 Figures 相似文献
26.
The magnetostratigraphic subdivision of the Plio-Pleistocene series in the Kinki district around Osaka in southwest Japan, based on NRM measurements of volcanic ash beds, is correlated with biostratigraphic and paleoclimatic marker beds as well as past sea level oscillations. At least 10 high sea level stands occurred in the study area between about 1.5 and 0.27 million years ago, all associated with relative warming. A significant change in the composition of flora, from Metasequoia to Fagus dominated assemblages, was observed around the Jaramillo event. 相似文献
27.
Overview of the MITI Nankai Trough Wells: A Milestone in the Evaluation of Methane Hydrate Resources 总被引:4,自引:0,他引:4
Yoshihiro Tsuji Hisashi Ishida Masaru Nakamizu Ryo Matsumoto Satoshi Shimizu 《Resource Geology》2004,54(1):3-10
Abstract. Bottom-simulating reflectors suggestive of the presence of methane hydrates are widely distributed below the ocean floor around Japan. In late 1999, drilling of the MITI Nankai Trough wells was conducted to explore this potential methane hydrate resource and a Tertiary conventional structure. The wells are located in the Northwest Pacific Ocean off Central Japan at a water depth of 945 m. A total of six wells were drilled, including the main well, two pilot wells, and three post survey wells at intervals of 10–100 m. All wells except the first confirmed the occurrence of hydrates based on logging-while-drilling, wire-line logging and/or coring using a pressure and temperature coring system in addition to conventional methods. Based on the various well profiles, four methane hydrate-bearing sand-rich intervals in turbidite fan deposits were recognized. Methane hydrates fill the pore spaces in these deposits, reaching saturation of up to 80 % in some layers. The methane hydrate-bearing turbiditic sand layers are less than 1 m thick, with a total thickness of 12–14 m. The bottom depth of high hydrate concentration correlates well with the depth of the bottom-simulating reflector. Based on these exploration results, the Japanese government inaugurated a 16-year methane hydrate exploitation program in 2001. 相似文献
28.
Shoji Arai Yohei Shimizu Tomoaki Morishita Yoshito Ishida 《Contributions to Mineralogy and Petrology》2006,152(3):387-398
We found fine-grained Fe-rich orthopyroxene-rich xenoliths (mainly orthopyroxenite) containing partially digested dunite fragments of Group I from Takashima, Southwest Japan. Orthopyroxenite veinlets, some of which contain plagioclase at the center, also replace olivine in dunite and wehrlite xenoliths of Group I. This shows high reactivity with respect to olivine of the melt involved in orthopyroxenite formation, indicating its high SiO2 activity. The secondary orthopyroxene of this type is characterized by low Mg# [= Mg/(Mg + total Fe) atomic ratio] (down to 0.73) and high Al2O3 contents (5–6 wt%). It is different in chemistry from other secondary orthopyroxenes found in peridotite xenoliths derived from the mantle wedge. Clinopyroxenes in the Fe-rich orthopyroxenite show a convex-upward REE pattern with a crest around Sm. This pattern is strikingly similar to that of clinopyroxenes of Group II pyroxenite xenoliths and of phenocrystal and xenocrystal clinopyroxenes, indicating involvement of similar alkali basaltic melts. The Fe-rich orthopyroxenite xenoliths from Takashima formed by reaction between evolved alkali basalt melt and mantle olivine; alkali basalt initially slightly undersaturated in silica might have evolved to silica-oversaturated compositions by fractional crystallization at high-pressure conditions. The Fe-rich orthopyroxenites occur as dikes within the uppermost mantle composed of dunite and wehrlite overlying pockets of Group II pyroxenites. The orthopyroxene-rich pyroxenites of this type are possibly common in the uppermost mantle beneath continental rift zones where alkali basalt magmas have been prevalent. 相似文献
29.
Hiroshi Ishida 《Boundary-Layer Meteorology》1989,47(1-4):71-84
Based on the data from an array of buoys during the JASIN-1978 field experiment made in an area northwest of Scotland, power spectra of surface wind speed and air temperature over the ocean in the mesoscale frequency range were studied. The averaged composite spectrum of wind speed for the whole period shows the existence of a spectral gap in the frequency range from 10–4 to 5 × 10–3 Hz. However, significant peaks in this range are often seen in particular spectra under certain weather conditions. Mesoscale spectral peaks of wind speed occur in 14 segments of the data record, approximately 10% of the total duration of the observations. In 4 of these segments, the mesoscale spectral peaks of both wind speed and air temperature occurred simultaneously. Several wave patterns of mesoscale atmospheric disturbances when mesoscale spectral peaks were seen are derived from phase differences between buoys. Significant mesoscale peaks in spectra appear in relatively strong winds and unstable or near-neutral atmospheric conditions, and none in stable atmospheric conditions. A criterion of wind speed and atmospheric stability is found for the mesoscale spectral peak appearance. 相似文献
30.
Katsuhiko Ishida 《地震工程与结构动力学》1985,13(6):799-825
This paper presents some results on the following subjects obtained from in-situ forced vibration tests and earthquake observations. (1) The characteristics of the radiation damping of soil-foundation interaction systems vs. non-dimensional frequency a0 (=ωr/Vs) were experimentally estimated by the equivalent damping ratios hH ( = K′H/2KH) and hR ( = K′R/2KR), which were defined by complex stiffnesses 1KH (= KH + iKH) and 1KR (= KR + iK′R) of soil. The results for hH and hR of base rock were compared with those of soft soil. (2) A comparative study of experimental and theoretical results was made. The theoretical results were obtained from elastic half-space theory. (3) A semi-empirical equation to estimate the equivalent S-wave velocity for the elastic half-space model is proposed here, considering the effects of layered media. (4) Various comparisons of the results of 1 KH, 1 KR, hH and hR of forced vibration tests and earthquake observations were made. 相似文献