Roles of vertical turbulent mixing in the ocean response to Typhoon Rex (1998)     

Akiyoshi Wada  Hiroshi Niino  Hideyuki Nakano 《Journal of Oceanography》2009,65(3):373-396

How the role of vertical turbulent mixing (VTM) in sea surface cooling (SSC) varies with the moving speed of a tropical cyclone was examined for Typhoon Rex (1998) by using the Meteorological Research Institute Community Ocean Model (MRI.COM). The MRI.COM well reproduced TRMM/TMI three-day mean sea surface temperature (SST) fields along Rex’s track. During the fast-moving phase of Rex, SSC simulated by the MRI.COM was caused by shear-induced VTM on the right side of the track. During the slowly-moving phase, on the other hand, the Ekman-pumping area mostly overlapped the VTM area right behind Rex’s center. During the recurvature phase, cool water transported by the upwelling was more efficiently entrained into a mixed layer by the VTM for nearly a 1 near-inertial period after the passage of Rex. We then modified the entrainment formulation of Deardorff (1983), which was incorporated into a slab mixed-layer ocean model (SOM) so as to fit to the results simulated by the MRI.COM. The principal modifications are as follows: (1) consideration of turbulent kinetic energy (TKE) production caused by surface wave breaking; (2) increase in the coefficient for estimating dissipation to balance with TKE production due to turbulent transport; and (3) changing the initial guess for the critical Richardson number. These modifications led to an improvement of SST simulations by the SOM. The impact of the modifications on simulated SSTs turned out to be more significant than the impacts of initial mixed-layer depth and the difference between diurnally-varying and daily mean short-wave radiation.  相似文献   

Upwelling of oxygen-depleted water (Sumishio) in Omura Bay,Japan     

Tetsuya Takahashi  Hideaki Nakata  Keiji Hirano  Kazumi Matsuoka  Mitsunori Iwataki  Hitoshi Yamaguchi  Tomoyuki Kasuya 《Journal of Oceanography》2009,65(1):113-120

Wind-induced circulation and the distribution of hypoxia corresponding to the upwelling of oxygen-depleted water (called “Aoshio” in Japan and “Sumishio” locally in Omura Bay) in Omura Bay, Japan, was examined field observations and by three-dimensional modeling. During the calm weather in summer, well-mixed strait water, in rich oxygen at the mouth of the bay intruded into the middle layer of the bay, southward and northward along the west and east coast, respectively, forming basin-scale cyclonic circulation. A stagnant water mass was formed below the center of this cyclonic circulation, and it became hypoxic water. As a result of the prevailing strong southeast (northeast) wind, the bottom hypoxia moved in a southeasterly (northeasterly) direction. This induces the upwelling of hypoxic water, accompanied by mass mortality of marine organisms.  相似文献   

Seasonal change of oceanographic conditions and chlorophyll <Emphasis Type="Italic">a</Emphasis> vertical distribution in the southwestern Okhotsk Sea during the non-iced season     

Hiromi Kasai  Yoshiyuki Nakano  Tsuneo Ono  Atsushi Tsuda 《Journal of Oceanography》2010,66(1):13-26

Seasonal changes in oceanographic conditions related to primary productivity was investigated in the southwestern Okhotsk Sea during non-iced seasons, using the observation data conducted in 2000∼2006. Based on hydrographic characteristics, the studied area could be classified into two regions, the Coastal Region which is influenced under the Soya Warm Current and the Forerunner Water of the Soya Warm Current, and the Offshore Region where the Intermediate Cold Water was located in the subsurface layer. This study is the first report on seasonal change of nutrient and chlorophyll a concentrations in the offshore region of the southwestern Okhotsk Sea. Variability of concentrations of chlorophyll a and nutrients is temporally and regionally high in the Coastal Region. The maximum chlorophyll a concentration in April was observed at the surface layer of both regions. The most remarkable feature on the vertical structure in the Offshore Region was the consistent existence of the Intermediate Cold Water and the development of seasonal thermocline in the subsurface layer during summer and autumn. The stratification formed within the euphotic zone in the Offshore Region resulted in the formation of the subsurface chlorophyll a maximum (SCM) from May to October. Throughout the research period, although less amplitude of nutrients at the surface was observed in the Coastal Region than that in the Offshore Region, comparable amplitude of chlorophyll a concentration was observed between regions. These results suggested differences of environmental conditions for primary production between the two regions. Depending on the presence of SCM, relationships between chlorophyll a concentration at the sea surface and chlorophyll a standing stock within the euphotic layer were different. At most stations with SCM, the surface chlorophyll a concentration was lower than 0.6 mg m-3. This suggests that the presence of SCM and the chlorophyll a standing stock within the euphotic layer may be estimated using the surface chlorophyll a concentration from spring to autumn in the studied area.  相似文献   

Encystment and excystment of <Emphasis Type="Italic">Gyrodinium instriatum</Emphasis> Freudenthal et Lee     

Tomoyuki Shikata  Sou Nagasoe  Tadashi Matsubara  Yasuhiro Yamasaki  Yohei Shimasaki  Yuji Oshima  Takuji Uchida  Ian R. Jenkinson  Tsuneo Honjo 《Journal of Oceanography》2008,64(3):355-365

In the present study, we have investigated the conditions influencing encystment and excystment in the dinoflagellate Gyrodinium instriatum under laboratory conditions. We incubated G. instriatum in modified whole SWM-3 culture medium and in versions of modified SWM-3 from which NO₃ ⁻, PO₄ ³⁻, NO₃ ⁻ + PO₄ ³⁻, or Si had been omitted and observed encystment. Percentage encystment was high in the media without N and without P, while the percentage encystment in the medium lacking both N and P was highest. Moreover, to investigate N or P concentration which induced the encystment, Gyrodinium instriatum was also incubated in media with different concentrations of inorganic N and P; the concentrations of NO₂ ⁻ + NO₃ ⁻ and PO₄ ³⁻ were measured over time. The precursors of cysts appeared within 2 or 3 days of a decrease in NO₂ ⁻ + NO₃ ⁻ or PO₄ ³⁻ concentration to values lower than 1 μM or 0.2 μM, respectively. When cysts produced in the laboratory were incubated, we observed excystment after 8–37 days, without a mandatory period of darkness or low temperature. We incubated cysts collected from nature at different temperatures or in the dark or light and observed excystments. Natural cysts excysted at temperatures from 10 to 30°C, in both light and dark, but excystment was delayed at low temperatures. These studies indicate that G. instriatum encysts in low N or P concentration and excysts over a wide temperature range, regardless of light conditions, after short dormancy periods.  相似文献   

Simple coprecipitation method combined with low-background γ-spectrometry: Determination of 7Be, 137Cs, 210Pb, and radium and thorium isotopes in small-volume coastal water samples     

Yusuke Nakano  Mutsuo Inoue  Kazuhisa Komura 《Journal of Oceanography》2008,64(5):713-717

Application of a coprecipitation method combined with low-background γ-spectrometry allowed the isolation of ⁷Be, ¹³⁷Cs, ²¹⁰Pb, and radium and thorium isotopes together with BaSO₄, Fe(OH)₃, or AMP/Cs in 18 L of coastal water. This simple method showed high chemical yields of 77–91% (mean, 85%) for ²¹⁰Pb and radium isotopes, 87–92% (mean, 91%) for 7Be and thorium isotopes, and 98% for ¹³⁷Cs. The activity of the nuclides showed good reproducibility with standard deviations of 1–8%, while the deviation of activity in particle-reactive ²¹⁰Pb (32%) and ⁷Be (21%) in filtered water samples was exceptionally large.  相似文献   

Characteristics of earthquake-induced landslides in a heavy snowfall region—landslides triggered by the northern Nagano prefecture earthquake, March 12, 2011, Japan   总被引：1，自引：0，他引：1  

Baator Has  Tomoyuki Noro  Kiyoteru Maruyama  Akira Nakamura  Kiichiro Ogawa  Satoshi Onoda 《Landslides》2012,9(4):539-546

The northern Nagano Prefecture earthquake, M_JMA?6.7 (Mw?6.2), which is inferred to have been triggered by the huge (Mw?9.0) March 11, 2011 Tohoku earthquake, occurred on March 12, 2011, in northern Nagano Prefecture, an area in Japan famous for heavy snowfall. A large number of landslides were triggered by the 12 March earthquake, and it caused building damage in the area of the epicenter. To clarify characteristics of the distribution and dynamic behavior of these landslides, we analyzed aerial photographs and conducted field surveys in and around the epicentral area. Large-scale landslides with long distance run-outs are a remarkable characteristic of the landslides induced by this earthquake. The long travel distance is considered to be related to the thick snowpack at the time the earthquake occurred. Moderate scale deep-seated landslides and shallow landslides were also observed in the study area. Based on an analysis of landslides with the active fault on which the earthquake is believed to have occurred, most of these landslides were distributed on the hanging wall of the active fault, within a distance of 12?km from the fault.  相似文献   

Performances of Landfill Liners under Dry and Wet Conditions     

Saravanan Mariappan  Masashi Kamon  Faisal Haji Ali  Takeshi Katsumi  Tomoyuki Akai  Toru Inui  Masaki Nishimura 《Geotechnical and Geological Engineering》2011,29(5):881-898

This paper addresses the study conducted on the performance of landfill liner interface parameters. Interface shear strength parameters for various combinations of 9 different lining materials were studied and presented in this paper. This comprehensive testing program covers the interfaces between: (1) soil and compacted clay liner (CCL), (2) geomembrane (HDPEs or PVC) and soil, (3) geosynthetic clay liner (GCL)/CCL and soil, (4) geomembrane and geotextile, (5) geotextile and soil, (6) geotextile and GCL/CCL, and (7) geomembrane and GCL/CCL. The experiments were conducted for both at dry or optimum moisture condition and at saturated or wet condition. The interface performance under both conditions were compared to access the material performances. Tabulated summaries of interface test data under dry or optimum moisture condition (OMO) and saturated or wet condition are presented in the paper.  相似文献   

Effects of large-scale wind on the Kuroshio path south of Japan in a 60-year historical OGCM simulation     

Hiroyuki Tsujino  Shiro Nishikawa  Kei Sakamoto  Norihisa Usui  Hideyuki Nakano  Goro Yamanaka 《Climate Dynamics》2013,41(9-10):2287-2318

The effects of large-scale wind forcing on the bimodality of the Kuroshio path south of Japan, the large meander (LM) and non-large meander (NLM), were studied by using a historical simulation (1948–2007) with a high-resolution Ocean general circulation models (OGCM). The Kuroshio in this simulation spent much time in the NLM state, and reproduced several aspects of its long-term path variability for the first time in historical OGCM simulation, presumably because the eddy kinetic energy was kept at a moderate level. By using the simulated fields, the relationships between wind forcing (or Kuroshio transport) and path variation proposed by past studies were tested, and specific roles of eddies in those variations were investigated. The long-term variation of the simulated net Kuroshio transport south of Japan was largely explained by the linear baroclinic Rossby wave adjustment to wind forcing. In the simulated LM events, a triggering meander originated from the interaction of a wind-induced positive sea surface height (SSH) anomaly with the upstream Kuroshio and was enlarged by cyclonic eddies from the recirculation gyre. The cyclonic eddy of the trigger meander was followed by a sizable anticyclonic eddy on the upstream side. Subsequently, a weak (strong) Kuroshio favored the LM (NLM). The LM tended to be maintained when the Kuroshio transport off southern Japan was small, and increasing Kuroshio transport promoted decay of an existing LM. The supply of disturbances from upstream, which is related to the wind-induced SSH variability at low latitudes, contributed to the maintenance of an existing LM.  相似文献   

Simulating present climate of the global ocean–ice system using the Meteorological Research Institute Community Ocean Model (MRI.COM): simulation characteristics and variability in the Pacific sector     

Hiroyuki Tsujino  Mikitoshi Hirabara  Hideyuki Nakano  Tamaki Yasuda  Tatsuo Motoi  Goro Yamanaka 《Journal of Oceanography》2011,67(4):449-479

A long-term spin-up and a subsequent interannual simulation are conducted for the ocean–ice component of the climate model intercomparison project (CMIP)-class earth system model of the Japan Meteorological Agency/Meteorological Research Institute. This experiment has three purposes: first is to assess the ability of our model with the Coordinated Ocean–ice Reference Experiments (COREs) forcing in reproducing the present ocean-climate; second is to understand the ocean-climate variability for the past 60 years; third is to present an example of evaluating an ocean–ice interannual variability simulation. The Pacific Ocean is focused on for the last two purposes. After integrating for about 1500 years with repeated use of a detrended CORE interannual forcing, the model reaches a quasi-steady state where the present climate is reproduced satisfactorily. Then, the interannual variability simulation is conducted with the retrieved forcing trend and the result is analyzed. The simulation is successful at reproducing the long-term variability in the Pacific and surrounding oceans. Brief analyses of the tropical and mid-latitude upper layer, deep circulation, and the Arctic sea ice are presented. A caveat in treating other parts of the globe is due to the recent intense convection in the Southern Ocean caused by a remarkably increasing trend of the Southern Hemisphere westerly. Overall, the current simulation with our CMIP-class ocean–ice model is shown to be useful for studying the present ocean-climate variability, specifically in the Pacific sector. It could also be used as a benchmark control experiment that facilitates further research, model development, and intercomparison.  相似文献   

Behavior of zircon in the upper-amphibolite to granulite facies schist/migmatite transition, Ryoke metamorphic belt, SW Japan: constraints from the melt inclusions in zircon     

Tetsuo Kawakami  Isao Yamaguchi  Akira Miyake  Tomoyuki Shibata  Kenshi Maki  Takaomi D. Yokoyama  Takafumi Hirata 《Contributions to Mineralogy and Petrology》2013,165(3):575-591

Behavior of zircon at the schist/migmatite transition is investigated. Syn-metamorphic overgrowth is rare in zircon in schists, whereas zircon in migmatites has rims with low Th/U that give 90.3 ± 2.2 Ma U–Pb concordia age. Between inherited core and the metamorphic rim, a thin, dark-CL annulus containing melt inclusion is commonly developed, suggesting that it formed contemporaneous with the rim in the presence of melt. In diatexites, the annulus is further truncated by the brighter-CL overgrowth, suggesting the resorption and regrowth of the zircon after near-peak metamorphism. Part of the zircon rim crystallized during the solidification of the melt in migmatites. Preservation of angular-shaped inherited core of 5–10 μm in zircon included in garnet suggests that zircon of this size did not experience resorption but developed overgrowths during near-peak metamorphism. The Ostwald ripening process consuming zircon less than 5–10 μm is required to form new overgrowths. Curved crystal size distribution pattern for fine-grained zircons in a diatexite sample may indicate the contribution of this process. Zircon less than 20 μm is confirmed to be an important sink of Zr in metatexites, and ca. 35-μm zircon without detrital core are common in diatexites, supporting new nucleation of zircon in migmatites. In the Ryoke metamorphic belt at the Aoyama area, monazite from migmatites records the prograde growth age of 96.5 ± 1.9 Ma. Using the difference of growth timing of monazite and zircon, the duration of metamorphism higher than the amphibolite facies grade is estimated to be ca. 6 Myr.  相似文献