Deep convection in a lake triggered by wind: Two-dimensional numerical experiments with a nonhydrostatic model     

Kazunori Akitomo  Kiyoshi Tanaka  Toshiyuki Awaji  Norihisa Imasato 《Journal of Oceanography》1995,51(2):171-185

We have investigated the fundamental processes of deep convection in a lake at high latitudes triggered by wind during spring or autumn and the associated deep water formation, executing vertically two-dimensional numerical experiments with a nonhydrostatic model. The water column in which a relatively cold mixed layer overlies a relatively warm layer becomes unstable, when the Ekman convergence on the shore due to along-shore wind deepens the mixed layer below the compensation depth, where water densities in both layers becomes equal to each other because of the thermobaric effect. At the onset of deep convection, the critical Rayleigh number agrees with that predicted by the linear theory. The onset time of deep convection is inversely proportional to the magnitude of wind stress. On the other hand, the onset time is minimal when water temperature in the mixed layer _m is 3.1°C because a change of _m has two effects oppositely acting on the stability of the water column. After the first onset, deep convection occurs intermittently for a few days. The sinking of the mixed layer water occurs in a thermal-like shape, and its amount is 4184% of the time-integrated Ekman transport when _m 3°C while it decreases to less than 10% for _m lower than 1.5°C. The present process can explain 30% of the amount of deep water renewal which is expected from the observation in Lake Baikal.  相似文献   

Diagenetic deposition of manganese in sediment of a historically meromictic lake,Lake Suigetsu,Japan     

Toshiyuki Masuzawa  Yasushi Kitano 《Journal of Oceanography》1982,38(2):73-80

Vertical profiles of manganese concentration in interstitial waters and of manganese and iron contents in five chemically-separated fractions of sediments have been studied in a sediment core (73 cm long) from a meromictic lake, Lake Suigetsu, which changed from freshwater to brackish conditions in 1664 A.D. The interstitial waters show a minimum manganese concentration of 0.13 ppm near a depth of 10 cm and a maximum of 26 ppm near 65 cm in the core. A predominant amount of manganese, up to 0.17%, is found in the hydrogen peroxide-soluble fraction of sediments in layers above a depth of 52 cm. It is suggested that the manganese is included in stable iron sulfides such as pyrite. Manganese, which diffuses upward from the lower layer, is thought to be deposited along with stable iron sulfide during diagenetic formation of the latter near a depth of 10 cm in the core.  相似文献   

Formation, Distribution and Volume Transport of the North Pacific Intermediate Water Studied by Repeat Hydrographic Observations     

Takashi Miyao  Koichi Ishikawa 《Journal of Oceanography》2003,59(6):905-919

In order to examine the formation, distribution and transport of North Pacific Intermediate Water (NPIW), repeated hydrographic observations along several lines in the western North Pacific were carried out in the period from 1996 to 2001. NPIW formation can be described as follows: (1) Oyashio water extends south of the Subarctic Boundary and meets Kuroshio water in intermediate layers; (2) active mixing between Oyashio and Kuroshio waters occurs in intermediate layers; (3) the mixing of Oyashio and Kuroshio waters and salinity minimum formation around the potential density of 26.8σ_θ proceed to the east. It is found that Kuroshio water flows eastward even in the region north of 40°N across the 165°E line, showing that Kuroshio water extends north of the Subarctic Boundary. Volume transports of Oyashio and Kuroshio components (relative to 2000 dbar) integrated in the potential density range of 26.6–27.4σθ along the Kuroshio Extension across 152°E–165°E are estimated to be 7–8 Sv (10⁶ m³s⁻¹) and 9–10 Sv, respectively, which is consistent with recent work. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Application of Sensitivity Analysis Using an Adjoint Model for Short-Range Forecasts of the Kuroshio Path South of Japan     

Yoichi Ishikawa  Toshiyuki Awaji  Nobumasa Komori  Takahiro Toyoda 《Journal of Oceanography》2004,60(2):293-301

A sensitivity experiment has been performed by assimilating altimetric data into a 1.5-layer primitive equation model as a first attempt to examine the impact of initialization on forecasts of the Kuroshio path variability south of Japan. By exploiting the advantage of an adjoint model, our approach clearly shows that a small meander off Shikoku Island has a large impact on the prediction of meander growth in the Kuroshio region. Further, the strengthening of the Kuroshio current and its recirculation clearly becomes an important factor in the development of the meander. These results demonstrate the effectiveness of our assimilation approach in identifying efficient initialization schemes on numerical forecasting of the Kuroshio south of Japan and should help in the construction of an effective observing system for improving the forecasting. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Study on the oceanic environments relating to the marine living resources     

Toshiyuki Hirano 《Journal of Oceanography》1986,42(6):490-501

This is a review of the study on the oceanic environments relating to the marine living resources carried out since 1947, during more than 35 years which are the period of the authors oceanographic research life for fisheries. Its content consists of describing the outlines of, (1) the oceanographic study of the Subarctic Region of the Northwestern Pacific as the salmon living waters, (2) the study on dilution processes of the effluent in the coastal waters in relation to marine pollution, (3) the oceanographic study on transportation and diffusion of fish eggs and larvae in relation to the recruitment of living resources and (4) the study on forecasting of the fisheries and oceanographic conditions, and a short note on direction of fisheries oceanography expected to be studied in the future.  相似文献   

Temporal Variability of High Vertical Wavenumber Shear over the Izu-Ogasawara Ridge     

Maki?NagasawaEmail author  Toshiyuki?Hibiya  Naoki?Furuichi  Shogo?Takagi 《Journal of Oceanography》2005,61(6):1101-1105

Recent numerical studies (Hibiya et al., 1996, 1998, 2002) showed that the energy cascade across the internal wave spectrum down to small dissipation scales was under strong control of parametric subharmonic instabilities (PSI) which transfer energy from low vertical mode double-inertial frequency internal waves to high vertical mode near-inertial internal waves. To see whether or not the numerically-predicted energy cascade process is actually dominant in the real deep ocean, we examine the temporal variability of vertical profiles of horizontal velocity observed by deploying a number of expendable current profilers (XCPs) at one location near the Izu-Ogasawara Ridge. By calculating EOFs, we find the observed velocity profiles are dominated by low mode semidiurnal (∼double-inertial frequency) internal tides and high mode near-inertial internal waves. Furthermore, we find that the WKB-stretched vertical scales of the near-inertial current shear are about 250 sm and 100 sm. The observed features are reasonably explained if the energy cascade down to small dissipation scales is dominated by PSI.  相似文献   

Can the visualization of rip currents prevent drowning accidents? Consideration of the effect of optimism bias     

Endo  Shintaro  Shimada  Ryo  Ishikawa  Toshinori  Komine  Tsutomu 《Natural Hazards》2022,110(3):2017-2033

Drowning accidents at beach in Japan are caused by rip currents. To reduce these accidents, a new technology that can detect rip currents and notify beachgoers by using the Internet of Things (IoT) and Artificial Intelligence (AI) was proposed. However, studies on the effect of visualizing rip currents or considering the effect of optimism bias have not been conducted. This study investigates if visualization of rip currents might help in preventing drowning accidents, while considering the effect of optimism bias. The participants were 90 Japanese beachgoers. They were asked to answer questions based on their knowledge of the beach and rip currents, their optimism bias regarding rip currents, and awareness with or without visualization. The results of the analyses suggest that despite optimism bias, the visualization of rip currents increases the tendency of beachgoers to perceive and avoid rip currents. As described above, it was found that by visualizing the rip current, beachgoers were able to perceive and avoid rip currents. In addition, an understanding of rip currents is positively related to the intent to avoid rip currents even when rip currents are visualized. Therefore, it is necessary not only to enhance the avoidance tendency by visualizing rip currents, but also to further enhance knowledge of beachgoers to deepen the understanding of rip currents including the danger associated and methods to avoid them.

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A FEM-MPM hybrid coupled framework based on local shear strength method for simulating rainfall/runoff-induced landslide runout     

Zhu  Yulong  Ishikawa  Tatsuya  Zhang  Yafen  Nguyen  Binh T.  Subramanian  Srikrishnan Siva 《Landslides》2022,19(8):2021-2032

Landslides - Limited by the independence and its defects of each general software package, simultaneous analysis of runoff, seepage, and large-deformation analysis is still an inevitable challenge....  相似文献   

Nuclear field shift effect as a possible cause of Te isotopic anomalies in the early solar system—An alternative explanation of Fehr et al. (2006 and 2009)     

Frédéric Moynier  Toshiyuki Fujii  Francis Albarède 《Meteoritics & planetary science》2009,44(11):1735-1742

Abstract— We explore the possibility that Te isotopic anomalies measured in Ca‐Al‐rich inclusions (Fehr et al. 2009) and in leachates of carbonaceous chondrites (Fehr et al. 2006) may be due to mass‐independent effects controlled by nuclear field shift rather than to nucleosynthetic processes. Fehr et al.'s spectrum of mass‐independent anomalies of Te isotopes shows a smooth correlation with mass number and nuclear charge distribution. Ratios of even to odd isotopes, as the ¹²⁵Te/¹²⁶Te ratio used by these authors for normalization are particularly prone to nuclear field shift effects. We show that the alternative normalization of isotopic ratios to ¹³⁰Te/¹²⁶Te strongly reduces the trend of isotopic fractionation with mass number, leaving only ¹²⁵Te as truly anomalous. For both normalizations (¹²⁵Te/¹²⁶Te and ¹³⁰Te/¹²⁶Te), Fehr et al.'s results fit the theory of Bigeleisen (1996), which suggests that the nuclear field shift effect can potentially account for the observed Te isotope abundances, as an alternative to nucleosynthetic processes. We propose that these mass‐independent effects may be acquired during accretion of sulfides from the solar nebula.  相似文献   

Tectonic setting of high-Mg andesite magmatism in the SW Japan arc: K–Ar chronology of the Setouchi volcanic belt     

Yoshiyuki Tatsumi  Naoto Ishikawa  Ken Anno  Kyoichi Ishizaka  Tetsumaru Itaya 《Geophysical Journal International》2001,144(3):625-631

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