Dilution of North Pacific Intermediate Water studied with chlorofluorocarbons     

Yutaka W. Watanabe  Koh Harada  Kimitoshi Ishikawa 《Journal of Oceanography》1995,51(2):133-144

Assessment was made of residual ratio of North Pacific Intermediate Water (NPIW) produced in subpolar region of the North Pacific using chlorofluorocarbons, CFC-11 and CFC-12 (CCl₃F and CCl₂F₂), along 175°E. NPIW on density horizons less than 26.80 remained more than 80% north of 30°N. It was suggested that new NPIW laterally spreads over the northern North Pacific without hardly being diluted by the surroundings. For density horizons greater than 26.80 north of 30°N, NPIW remained less than 60%. The difference in the residual ratio between <26.80 and >26.80 north of 30°N suggests that NPIW is produced on density horizons less than 26.80, which contacts the atmosphere in the subpolar region, and that NPIW is diluted by upwelling deep water on density horizons greater than 26.80 in high latitude of the North Pacific. NPIW on a density horizon of 26.80 remained about 50% south of 30°N. The decrease in the horizontal distribution of the residual ratio of NPIW suggests that half the new NPIW produced in the subpolar region is laterally spread over the North Pacific with the southward movement of NPIW.  相似文献   

Statistical Evidence for Asymmetry in ENSO–IOD Interactions     

R. Kartika Lestari  Tieh-Yong Koh 《大气与海洋》2016,54(5):498-504

The interaction between the El Niño–Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) has been noted in many previous studies. However, the interaction is often presumed to exist in a robust manner. This paper questions this assumption and looks for statistical evidence for the robust existence of the ENSO–IOD interaction rather than chance co-occurrences. Consistent definitions of ENSO and IOD events were developed so that ENSO and IOD events identified are comparable in nature, strength, persistence, and time of occurrence during the year, relative to their natural variability. We applied a combinatorial probability test to the probability tables of ENSO and IOD events to test for robustness of our results and those computed from two published works. Our findings show that there is an asymmetry in the interaction between ENSO and IOD. The interaction between El Niño (EN) and the positive and negative phases of the IOD (pIOD and nIOD, respectively) is more robust, enhancing the EN–pIOD co-occurrence and suppressing the EN–nIOD co-occurrence. On the other hand, the interaction between La Niña (LN) and either phase of the IOD cannot be said to exist with the same robustness; the interaction suppresses LN–pIOD co-occurrence, but the occurrence of LN–nIOD might be coincidental. Further research is needed to determine the cause and mechanisms for the asymmetry in the interaction between LN and pIOD/nIOD.  相似文献   

Tidal variability in benthic silicic acid fluxes and microphytobenthos uptake in intertidal sediment     

Aude Leynaert  Sorcha Ní Longphuirt  Soonmo An  Jae-Hyun Lim  Pascal Claquin  Jacques Grall  Bong Oh Kwon  Chul Hwan Koh 《Estuarine, Coastal and Shelf Science》2011

Silicic acid (DSi) benthic fluxes play a major role in the benthic–pelagic coupling of coastal ecosystems. They can sustain microphytobenthos (MPB) development at the water–sediment interface and support pelagic diatoms when river DSi inputs decrease. DSi benthic fluxes have been studied at the seasonal scale but little is known about their dial variations. This study measured the amplitude of such variations in an intertidal area over an entire tidal cycle by following the alteration of DSi pore water concentrations at regular intervals over the flood/ebb period. Furthermore we independently estimated the potential DSi uptake by benthic diatoms and compared it to the variations of DSi pore water concentrations and fluxes. The microphytobenthos DSi demand was estimated from primary production measurements on cells extracted from the sediment. There were large changes in DSi pore water concentration and a prominent effect of tidal pumping: the DSi flushed out from the sediment at rising tide, occurs in a very short period of time, but plays a far more important role in fueling the ecosystem (800 μmol-Si m⁻² d⁻¹), than diffusive fluxes occurring throughout the rest of the tidal cycle (2 μmol-Si m⁻² d⁻¹). This process is not, to our knowledge, currently considered when describing the DSi cycling of intertidal sediments. Moreover, there was a large potential MPB requirement for DSi (812 μmol-Si m⁻² d⁻¹), similar to the advective flow periodically pumped by the incoming tide, and largely exceeded benthic diffusive fluxes. However, this DSi uptake by benthic diatoms is almost undetectable given the variation of DSi concentration profiles within the sediment.  相似文献   

Taxonomic studies on Korean marine benthic diatoms — LM and SEM observations of the diatom genus Amphora (Bacillariophyceae) from Korean tidal flats with the first recordings of A. arenicola, A. beaufortiana and A. maletractata var. constricta     

Jinsoon Park  Chul-Hwan Koh 《Ocean Science Journal》2012,47(2):101-112

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A Study Of The Atmospheric Boundary Layer Using Radon And Air Pollutants As Tracers     

Toshio Kataoka  Eiji Yunoki  Mitsuo Shimizu  Tadashige Mori  Osamu Tsukamoto  Yukitaka Ohashi  Ken Sahashi  Toshihiko Maitani  Koh’ichi Miyashita  Toru Iwata  Yoko Fujikawa  Akira Kudo  Roger H. Shaw 《Boundary-Layer Meteorology》2001,101(2):131-156

Concentrations of radon ²²²Rn andair pollutants, meteorological parametersnear the surface and vertical profiles of meteorological elements were measured atUchio (Okayama City, Okayama Prefecture, Japan) 12 km north from the coast ofthe Inland Sea of Japan. In the nighttime, the ²²²Rn concentration increased in the case of weak winds, but did not increase as much in the case of moderate or strong winds, as had been expected. In the daytime, the ²²²Rn concentrationheld at a slightly higher than average level for the period from sunrise to about 1100 JST. It is considered that this phenomenon is due to a period of morning calm, that is, a transition period from land breeze to sea breeze.NO, which is sensitive to traffic volume,brought information concerning advection.Oxidant concentrations,which reflect the availability of sunlight,acted in the reverse manner to ²²²Rnconcentrations. Thus, a set of ²²²Rn and air pollutants could provide useful information regarding the local conditions of the atmospheric boundary layer.  相似文献   

Seismic response of base isolated buildings including p-Δ effects of isolation bearings     

Chan Ghee Koh  Thambirajah Balendra 《地震工程与结构动力学》1989,18(4):461-473

In order to achieve a low isolation frequency, elastomeric bearings used for base isolation of buildings usually have low shear rigidity which leads to a significant reduction in the buckling load. The effects of compression load on the bearing behaviour are therefore an important consideration. A study of seismic response of base isolated buildings is presented in this paper, fully accounting for the P-Δ effects of isolation bearings. An analytical procedure is formulated that treats separately the superstructure and the supporting bearings and assembles the governing equations via the interaction forces at the base deck. The resulting equations are then solved step-by-step numerically. Numerical results obtained for a base isolated five-storey shear building show that neglecting the P-Δ effects can lead to considerable errors in the computed seismic response when the buckling safety factor of bearings is low.  相似文献   

Neutron Activation Analysis of Nine GSJ Sedimentary Rock Reference Samples     

Naomi AOTA  Yutaka MIYAMOTO  Sakae KOSANDA  Yasuji OURA  Toshiyuki OKUI  Koh SAKAMOTO 《Geostandards and Geoanalytical Research》1994,18(2):185-193

Nine rock reference samples "Sedimentary rock series" issued by the Geological Survey of Japan (GSJ) were analysed for up to 31 elements by neutron activation analysis (NAA); 14MeV-NAA for Si and Al, fission track method for U, radiochemical and instrumental NAA for rare-earth elements, and instrumental NAA for the remaining elements, with reactor neutrons for the latter three. The present results are compared with reported values.  相似文献   

Ra in the Japan Sea and the residence time of the Japan Sea water     

Koh Harada  Shizuo Tsunogai 《Earth and Planetary Science Letters》1986,77(2)

The surface water of the Japan Sea contained²²⁶Ra of70 ± 4dpm m⁻³ which was nearly equal to that of the surface water in the North Pacific. The concentration of²²⁶Ra in the Japan Sea deep water below 500 m was151 ± 8dpm m⁻³, showing a vertically and regionally small variation. This concentration of²²⁶Ra in the deep water is unexpectedly high, because the Japan Sea deep water has a higher Δ¹⁴ C value by about 50‰ than the Atlantic deep water containing the same²²⁶Ra. One of the causes to be considered is larger contribution of²²⁶Ra from biogenic particles dissolving in the Japan Sea deep water, but the Japan Sea is not so fertile in comparison to the Bering Sea. The other more plausible cause is the internal ventilation of the Japan Sea water, which means that the residence time of the Japan Sea Proper water is considerably long although the water is vertically mixed fairly well especially in winter. The ventilation may supply some amounts of radiocarbon and oxygen but does not change the inventory of²²⁶Ra. The residence times of the Japan Sea deep water and of water within the Japan Sea are calculated by solving simultaneous equations for²²⁶Ra and¹⁴C with a three-box model to be 300–400 years and 700–1000 years, respectively.  相似文献   

Earthquake response spectra taking account of number of response cycles     

Kazuhiko Kawashima  Koh Aizawa 《地震工程与结构动力学》1986,14(2):185-197

Proposed is a new definition of earthquake response spectra, which takes account of the number of response cycles N. The Nth largest amplitude of absolute acceleration response of a linear oscilator with natural period T and damping ratio h, which is subjected to ground motion at its base, is defined as S_A(T, h, N). By defining a reduction factor η(T, h, N) as S_A(T, h, N)/S_A(T, h, 1), characteristics of η(T, h, N) were investigated based on 394 components of strong motion records obtained in Japan. Two practical empirical formulae to assess the reduction factor η(T, h, N) are proposed.  相似文献   

Tidal effects on variations of fresh–saltwater interface and groundwater flow in a multilayered coastal aquifer on a volcanic island (Jeju Island, Korea)     

Kue-Young Kim  Hyeonjeong Seong  Taehee Kim  Ki-Hwa Park  Nam-Chil Woo  Yoon-Suk Park  Gi-Won Koh  Won-Bae Park 《Journal of Hydrology》2006,330(3-4):525-542

We conducted various field studies at the seawater intrusion monitoring wells located in the eastern part of Jeju Island, Korea, to observe the tidal effect on groundwater–seawater flow in the coastal aquifer. Studies included monitoring the fluctuations of groundwater and tide levels, electrical and temperature logging, and 2-D heat-pulse flowmeter tests. According to time-series analysis, tidal effects on groundwater level reached up to 3 km inland from the coastline. Water-level variation was more sensitive to tidal fluctuations near the coast, and more related to rainfall toward inland areas. Temporal and spatial variations in the shape and location of the freshwater–saltwater interface were analyzed using data from nine monitoring wells. The results indicated that the interface toe is located at a distance of 6–8 km from the coastline and its location was related to geological layers present. Long-term seasonal variations revealed no major changes in the interface; minor variations were due to moving boundary conditions induced by tidal fluctuations. Using the two-dimensional heat-pulse flowmeter, groundwater flow directions and velocities at four tidal stages were measured on three monitoring wells drilled into the multilayered aquifers. This direct measurement enabled us to relate the differences of flow velocities and directions with geology and tidal fluctuations. Combining the results of EC logging and flowmeter tests, we found a zone where freshwater and saltwater moved alternately in opposite directions, as influenced by the tidal fluctuations. Integrating various physical logging and flowmeter data with water-level fluctuations improved our understanding of the behavior of fresh and seawater flow in the coastal aquifers.  相似文献