The coriolis effect against frontogenesis in steady buoyancy-driven circulation     

Akira Harashima  Yukio Oonishi 《Journal of Oceanography》1981,37(1):49-59

The Coriolis effect on frontogenesis in the transitional region between the inner bay and the outer ocean is studied by running several three-dimensional numerical experiments. The aim is to clarify what external parameters, including the transverse scale of the basin, control the phenomena. The characteristics of the front in each case are described by defining three diagnostic quantities, namely, the sharpness of the front, the intrusion of the front, and the buoyancy difference between the minimum buoyancy region and the surrounding part, as the existence of the minimum buoyancy region is closely related to frontogenesis. The three quantities are shown to depend on two nondimensional numbers,R _of (=f ⁻¹ L ^−2/3 F _b ^1/3 : defined as flux Rossby number) andR _ef (=ν _v ⁻¹ L ^−2/3 F _b ^1-3 H ²: defined as flux Reynolds number).  相似文献   

Regional distribution of dinoflagellate population off the coasts of Hokkaido in the Japan and Okhotsk seas from spring to Autumn, 1983     

Akira Miyazono  Takashi Minoda 《Journal of Oceanography》1990,46(3):96-106

The regional distribution of dinoflagellates was investigated in the surface waters surrounding Hokkaido in May, August, and October, 1983. Among the total of 92 species identified, 37 species appeared throughout the investigation period. A similarity analysis identified six assemblages at C_λ=0.66. It was shown that each assemblage was closely related to the currents and the water temperature. Assemblage I consisted of 80% of the total samples and was subdivided into two groups-cold and warm water species in the Tsushima Current. Cold water species were widely spread in the Tsushima and Soya Currents in May and shifted to the Low Saline Water in October while warm water species were dominant in the Tsushima and Soya Currents in October. The regional abundance of shellfish toxic dinoflagellates,Dinophysis fortii andProtogonyaulax tamarensis, was also revealed.  相似文献   

Interannual fluctuations in recruitment of walleye pollock in the Oyashio region related to environmental changes     

Osamu Shida  Tomonori Hamatsu  Akira Nishimura  Akifumi Suzaki  Jun Yamamoto  Kazushi Miyashita  Yasunori Sakurai 《Deep Sea Research Part II: Topical Studies in Oceanography》2007,54(23-26):2822

The Japanese Pacific walleye pollock (Theragra chalcogramma) stock is the largest stock of this species in Japanese waters. It is a key component of the Oyashio ecosystem. In southern Hokkaido waters, these fish spawn mainly during January and February near the mouth of Funka Bay (FB), and most eggs and larvae are transported into FB. During midsummer juvenile pollock migrate along the southern coast of Hokkaido to a nursery ground on the continental shelf off eastern Hokkaido (Doto area). However, some eggs and larvae are transported southward to the Tohoku region (TR). Transport depends largely on the Oyashio, which generally flows southward along the eastern coasts of Hokkaido and Tohoku. Thus, this stock has two different recruitment routes: FB–Doto and FB–TR. In the 1980s, when the southward flow of the Oyashio was strong, the number of age-2 pollock estimated from a virtual population analysis (VPA) indicated that recruitment to the entire stock remained at a medium level. In the 1990s, when the Oyashio weakened, strong year-classes occurred in 1991, 1994, and 1995, but not in the latter half of the 1990s. Juvenile catches in the TR by commercial fisheries, which can be taken as indices of recruitment level via FB–TR, were high during the 1980s and decreased in the 1990s. Although there was no significant difference in the average number of recruits between the 1980s and the 1990s as estimated from a VPA, the recruitment patterns differed between the two decades. Here, we propose that recruitment routes of this stock shifted in response to environmental changes.  相似文献   

The study of oceanic turbulent diffusion     

Okubo  Akira 《Journal of Oceanography》1983,39(6):327-331

Journal of Oceanography - It is indeed a great honor to receive the Oceanographical Society of Japan Prize (1983) for the study of oceanic turbulent diffusion. For this award I owe a great many...  相似文献   

Coastal Disturbance in Sea Level Propagating along the South Coast of Japan and Its Impact on the Kuroshio     

Akira?NaganoEmail author  Masaki?Kawabe 《Journal of Oceanography》2005,61(5):885-903

The coastal sea level propagating westward along the south coast of Japan and the impact of the disturbance on the generation of the Kuroshio small meander have been examined. The propagation occurs in sea level variations for periods shorter than 10 days and is remarkable for periods of 4–6 days. Characteristics of the 4–6 day component have been studied using the extended empirical orthogonal function (EEOF). The first and second modes of EEOF are almost in-phase throughout the south coast of Japan. The higher four modes of EEOF are significantly excited when the Kuroshio takes the non-large-meander path, and propagate westward with phase speeds of 2.8 m s⁻¹ (third and fourth modes) and 1.6 m s⁻¹ (fifth and sixth modes) in the Kuroshio region west of Mera in the Boso Peninsula. The analysis shows that more than 70% of the small meanders generate in two months after a significant propagating disturbance reaches south of Kyushu when the velocity of the Kuroshio is high. This effect of coastal disturbance is examined by numerical experiments with a 2.5-layer model in which coastal disturbance is excited by vertical displacement of the upper interface. The result is that offshore displacement of the Kuroshio occurs southeast of Kyushu only in the case of significant upward displacement of the interface under the influence of a high Kuroshio velocity. The significant coastal disturbance, which is associated with upward displacement of the density interface, and a high Kuroshio velocity can therefore be important factors in generating small meanders.  相似文献   

Water wedge advancing along the interface between two homogeneous layers     

Akira Masuda  Yutaka Nagata 《Journal of Oceanography》1974,30(6):289-297

The behavior of the water wedge advancing along the interface between two homogeneous layers is investigated experimentally. The horizontally intruding wedge is strongly influenced by the detailed structure of the interface, even when the interface is sharp enough for its position to be visually determined. Within our experimental range, the intrusion velocity is very slow and depends on the thickness of the interface along which the water wedge intrudes. The wedge length is well described by the relation which is derived using an analogy to the linearly stratified case. The results could be useful for understanding the generation mechanism of the oceanic microstructure.  相似文献   

A skewed eddy of Batchelor-modon type     

Akira Masuda 《Journal of Oceanography》1988,44(4):189-199

A Batchelor-modon eddy is a highly specialized nonlinear vortex pair, whose potential vorticity depends linearly on the stream function viewed from the coordinates moving with the translation velocity of the eddy. To generalize it, a skewed model is developed by introducing a cubic nonlinearity in addition to the linear term. A perturbation analysis shows that the eddy region is no longer a circle but is elongated longitudinally or transversely according as the sign of the cubic term. Moreover, the eddy is slightly flattened or steepened. The cubic term increases or decreases the translation velocity, if the average radius and the amplitude are fixed. A numerical experiment on anf-plane is carried out to show that these skewed eddies retain their initial forms even after they turn a corner of the basin; they are as stable as (first-mode) standard Batchelor-modon eddies. The present skewed model gives a reasonable qualitative interpretation of deformed eddies which result from merging of two eddies or from initially Gaussian eddies near the boundary.  相似文献   

Microzooplankton standing crop in the western subtropical pacific off the Bonin Islands in winter, 1980     

Yoshinari Endo  Hiroshi Hasumoto  Akira Taniguchi 《Journal of Oceanography》1983,39(4):185-191

Quantitative data on the vertical distribution and biomass of microzooplankton are presented for the western subtropical Pacific west of the Bonin Islands in winter. Microzooplankton other than foraminifera and radiolarians showed similar vertical distribution to chlorophylla. Among microzooplankters, naked ciliates, tintinnids and copepod nauplii were dominant components both in number and volume. Naked ciliates were the most dominant, comprising 82.2 % and 47.7 % of the total microzooplankton by number and volume, respectively. Copepod nauplii, occupying less than 10 % by number, accounted for 35.7 % of the volume of all microzooplankton. Tintinnids contributed less to the microzooplankton standing crop, 12.6 % of the total by number and 17.3 % by volume. Calculated microzooplankton wet weight varied from 0.84 to 1.80 g m^?2 and corresponded to 9.9–18.1 % of net zooplankton weight. The relative abundance of microzooplankton to net zooplankton in this study is comparable to that previously reported in the tropical and subtropical Pacific Ocean, but a little higher than in oceanic subarctic areas.  相似文献   

Sea surface temperature observation by Global Imager (GLI)/ADEOS-II: Algorithm and accuracy of the product   总被引：1，自引：0，他引：1  

Futoki Sakaida  Kohtaro Hosoda  Masao Moriyama  Hiroshi Murakami  Akira Mukaida  Hiroshi Kawamura 《Journal of Oceanography》2006,62(3):311-319

A sea surface temperature (SST) retrieval algorithm for Global Imager (GLI) aboard the ADEOS-II satellite has been developed. The algorithm is used to produce the standard SST product in the Japan Aerospace Exploration Agency (JAXA). The algorithm for cloud screening is formed by combinations of various types of tests to detect cloud-contaminated pixels. The combination is changed according to the solar zenith angle, which enables us to detect clouds even in the sun glitter region in daytime. The parameters in the cloud-detection tests have been tuned using the GLI global observations. SST is calculated by the Multi-Channel SST (MCSST) technique from the detected clear pixels. Using drifting buoy measurements, match-up data are produced to derive the coefficients of the MCSST equations and to examine their performance. The bias and RMSE of the GLI SST are 0.03 K and 0.66 K for daytime and, −0.01 K and 0.70 K for nighttime, respectively.  相似文献   

Factors affecting preservation of coesite in ultrahigh‐pressure metamorphic rocks: Insights from TEM observations of dislocations within kyanite     

Tomoki Taguchi  Yohei Igami  Akira Miyake  Masaki Enami 《Journal of Metamorphic Geology》2019,37(3):401-414

To understand the preservation of coesite inclusions in ultrahigh‐pressure (UHP) metamorphic rocks, an integrated petrological, Raman spectroscopic and focussed ion beam (FIB) system–transmission electron microscope (TEM) study was performed on a UHP kyanite eclogite from the Sulu belt in eastern China. Coesite grains have been observed only as rare inclusions in kyanite from the outer segment of garnet and in the matrix. Raman mapping analysis shows that a coesite inclusion in kyanite from the garnet rim records an anisotropic residual stress and retains a maximum residual pressure of ~0.35 GPa. TEM observations show quartz is absent from the coesite inclusion–host kyanite grain boundaries. Numerous dislocations and sub‐grain boundaries are present in the kyanite, but dislocations are not confirmed in the coesite. In particular, dislocations concentrate in the kyanite adjacent to the boundary with the coesite inclusion, and they form a dislocation concentration zone with a dislocation density of ~10⁹ cm^?2. A high‐resolution TEM image and a fast Fourier transform‐filtered image reveal that a tiny dislocation in the dislocation concentration zone is composed of multiple edge dislocations. The estimated dislocation density in most of the kyanite away from the coesite inclusion–host kyanite grain boundaries is ~10⁸ cm^?2, being lower than that in kyanite adjacent to the coesite. In the case of a coesite inclusion in a matrix kyanite, using Raman and TEM analyses, we could not identify any quartz at the grain boundaries. Dislocations are not observed in the coesite, but numerous dislocations and stacking faults are developed in the kyanite. The estimated overall dislocation density in the coesite‐bearing matrix kyanite is ~10⁸ cm^?2, but a high dislocation density region of ~10⁹ cm^?2 is also present near the coesite inclusion–host kyanite grain boundaries. Inclusion and matrix kyanite grains with no coesite have dislocation densities of ≤10⁸ cm^?2. Dislocation density is generally reduced during an annealing process, but our results show that not all dislocations in the kyanite have recovered uniformly during exhumation of the UHP rocks. Hence, one of the key factors acting as a buffer to inhibit the coesite to quartz transformation is the mechanical interaction between the host and the inclusion that lead to the formation of dislocations in the kyanite. The kyanite acts as an excellent pressure container that can preserve coesite during the decompression of rocks from UHP conditions. The search for and study of inclusions in kyanite may be a more suitable approach for tracing the spatial distribution of UHP metamorphic rocks.  相似文献