Simulation of Formation and Spreading of Salinity Minimum Associated with NPIW Using a High-Resolution Model   总被引：1，自引：2，他引：1  

Hiroshi Ishizaki  Ichiro Ishikawa 《Journal of Oceanography》2004,60(2):463-485

A series of numerical experiments were conducted with a high-resolution (eddy-permitting) North Pacific model to simulate the formation and spreading of the salinity minimum associated with the North Pacific Intermediate Water (NPIW). It was found that two factors are required to simulate a realistic configuration of the salinity minimum: a realistic wind stress field and small-scale disturbances. The NCEP reanalyzed wind stress data lead to better results than the Hellerman and Rosenstein wind stress data, due to the closer location of the simulated Oyashio and Kuroshio at the western boundary. Small-scale disturbances formed by relaxing computational diffusivity included in the advection scheme promote the large-scale isopycnal mixing between the Oyashio and Kuroshio waters, simulating a realistic configuration of the salinity minimum. A detailed analysis of the Oyashio water transport was carried out on the final three-year data of the experiment with reduced computational diffusivity. Simulated transport of the Kuroshio Extension in the intermediate layer is generally smaller than the observed value, while those of the Oyashio and the flow at the subarctic front are comparable to the observed levels. In the Oyashio-Kuroshio interfrontal zone the zonally integrated southward transport of the Oyashio water (140–155°E) is borne by the eddy activity, though the time-mean flow reveals the existence of a coastal Oyashio intrusion. In the eastern part (155°E–180°) the zonally integrated transport of the Oyashio water indicates a southward peak at the southern edge of the Kuroshio Extension, which corresponds to the branching of the recirculating flow from the Kuroshio Extension. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Effects of presence of a circumpolar region on buoyancy-driven circulation     

I. Ishikawa  Y. Yamanaka  N. Suginohara 《Journal of Oceanography》1994,50(3):247-263

Effects of the presence of a circumpolar region on buoyancy-driven circulation are investigated by using an idealized numerical ocean model. Comparison of circulation and meridional density (heat) transport is made between a closed ocean and an ocean with a cyclic gap near its southern boundary. The presence of the circumpolar region leads to disconnection of the meridional overturning across the circumpolar region. And the circumpolar eastward flow reaches the bottom of the ocean. It is essential for this that the pycnocline is deeper than the bottom of the gap. Since the amount of the mass transported northward must return southward at the levels deeper than the bottom of the cyclic gap, the weak stratification, hence weak vertical geostrophic shear, at the deeper levels leads to inactive communication across the circumpolar region. Meridional heat transport across the circumpolar region is made mainly by horizontal diffusion for the ocean with the cyclic gap, while the contribution of the advection is dominant for the closed ocean. Sensitivity of meridional heat transport to change in horizontal diffusivity is studied. The meridional heat transport for the ocean with the cyclic gap is more sensitive than for the closed ocean. The change in heat transport occurs not only in the circumpolar region but also in the rest of the ocean. It is suggested that subgrid scale phenomena, especially mesoscale eddies, in the circumpolar region controls the whole ocean to a great extent.  相似文献   

State Estimation of the North Pacific Ocean by a Four-Dimensional Variational Data Assimilation Experiment   总被引：1，自引：0，他引：1  

Toshiyuki Awaji  Shuhei Masuda  Yoichi Ishikawa  Nozomi Sugiura  Takahiro Toyoda  Tomohiro Nakamura 《Journal of Oceanography》2003,59(6):931-943

A four-dimensional variational data assimilation system has been applied to an experiment to describe the dynamic state of the North Pacific Ocean. A synthesis of available observational records and a sophisticated ocean general circulation model produces a dynamically consistent dataset, which, in contrast to the nudging approach, provides realistic features of the seasonally-varying ocean circulation with no artificial sources/sinks for temperature and salinity fields. This new dataset enables us to estimate heat and water mass transports in addition to the qualification of water mass formation and movement processes. A sensitivity experiment on our assimilation system reveals that the origin of the North Pacific Intermediate Water can be traced back to the Sea of Okhotsk and the Bering Sea in the subarctic region and to the subtropical Kuroshio region further south. These results demonstrate that our data assimilation system is a very powerful tool for the identification and characterization of ocean variabilities and for our understanding of the dynamic state of ocean circulation. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

High parallelization efficiency in barotropic-mode computation of ocean models based on multi-grid boundary ghost area   总被引：1，自引：0，他引：1  

Hiroshi Ishizaki  Ichiro Ishikawa 《Ocean Modelling》2006,13(3-4):238-254

In general, barotropic-mode computation requires the largest communication time in ocean models because of its iterative nature, when parallel computation is performed based on regional partitioning. In this study, reduction in the overhead time included in the communication in the parallel computation of the barotropic mode is considered to achieve a high parallelization efficiency of ocean models. We verify that the reduction in the communication frequency based on the multi-grid boundary ghost area reduces the total communication time. We find that this is because the sum of several kinds of overhead time for communication occupies a fairly large part of the total communication time. We discuss the trade-off between the decrease in communication time and the increase in computation time due to increased boundary area in such cases, leading to a determination of a suitable width of the multi-grid boundary that minimizes the total required time. We also discuss the efficiencies of the one- and two-dimensional partitioning of the model domain, when a multi-grid boundary is used. In general, two-dimensional partitioning is more efficient than one-dimensional for large partitioning numbers.  相似文献   

Tidal energy balance in the Seto Inland Sea     

Tetsuo Yanagi  Hidetaka Takeoka  Hideshi Tsukamoto 《Journal of Oceanography》1982,38(5):293-299

The tidal volume transport in the Seto Inland Sea is calculated. The cross-section where the volume transport of the M₂ tide is zero, is located around the western part of Bisan Strait. The tidal energy dissipation of the M₂ tide by friction is 6.30×10¹⁶ ergs s^–1 in the Seto Inland Sea. The quality factorQ for the M₂ tide is 20.2. The total energy dissipation of the M₂, S₂, K₁ and O₁ tides is 7.99×10¹⁶ ergs s^–1.  相似文献   

A shipborne wave-recording system with digital data processing     

Keisuke Taira  Atsushi Takeda  Koji Ishikawa 《Journal of Oceanography》1971,27(4):175-186

A shipborne wave-recording system which consists of a sonic wave gauge, accelerometers, gyroscopes and a computer system is described. Signals from the measuring apparatus are fed directly into a shipborne digital computer system at a prescribed sampling rate. The time series of wave heights and the acceleration are transformed into Fourier series using an algorithm of Fast Fourier Transform. Errors contained in the observed wave heights due to ship motion are corrected in the Fourier series by using the Fourier coefficients for the vertical acceleration. Power spectra and waveforms can also be calculated in a short time with this system from Fourier coefficients. Examples of the observational results obtained in the central part of the East China Sea in 1969 are presented.  相似文献   

Detection of a new interstellar molecular ion, H2COH+ (protonated formaldehyde)     

Ohishi M  Ishikawa SI  Amano T  Oka H  Irvine WM  Dickens JE  Ziurys LM  Apponi AJ 《The Astrophysical journal》1996,471(1):L61-L64

A new interstellar molecular ion, H2COH+ (protonated formaldehyde), has been detected toward Sgr B2, Orion KL, W51, and possibly in NGC 7538 and DR21(OH). Six transitions were detected in Sgr B2(M). The 1(1,0)-1(0,1) transition was detected in all sources listed above. Searches were also made toward the cold, dark clouds TMC-1 and L134N, Orion (3N, 1E), and a red giant, IRC + 10216, without success. The excitation temperatures of H2COH+ are calculated to be 60-110 K, and the column densities are on the order of 10(12)-10(14) cm-2 in Sgr B2, Orion KL, and W51. The fractional abundance of H2COH+ is on the order of 10(-11) to 10-(9), and the ratio of H2COH+ to H2CO is in the range 0.001-0.5 in these objects. The values in Orion KL seem to be consistent with the "early time" values of recent model calculations by Lee, Bettens, & Herbst, but they appear to be higher than the model values in Sgr B2 and W51 even if we take the large uncertainties of column densities of H2CO into account. We suggest production routes starting from CH3OH may play an important role in the formation of H2COH+.  相似文献   

Amorphous interstellar grains: Wavelength dependence of far-infrared emission efficiency     

Junji Seki  Tetsuo Yamamoto 《Astrophysics and Space Science》1980,72(1):79-86

It is shown theoretically that the emission efficiency of amorphous grains with radii smaller than 100 Å has a _-1-dependence in the wavelength region longer than 100 , whereas those of crystalline, metallic, and larger amorphous grains are proportional to _-2 in far infrared. Astrophysical implications of the amorphous grains are discussed.  相似文献   

Stratigraphy and optically stimulated luminescence (OSL) dating of a Quaternary sequence along the Dong Nai River, southern Vietnam   总被引：1，自引：0，他引：1  

Toshiyuki Kitazawa  Takahiro Nakagawa  Tetsuo Hashimoto  Masaaki Tateishi 《Journal of Asian Earth Sciences》2006,27(6):788-804

The pre-Holocene Cenozoic sequence outcrops in the terrestrial part of the eastern margin of the Mekong Basin. However, the stratigraphy of the sequence is still unclear. Its detailed stratigraphy and chronology were therefore studied along the Dong Nai River, southern Vietnam, and the lithofacies and the relations among the formations were investigated from the outcrops. The ages of the deposits were determined by using optically stimulated luminescence (OSL) dating.The Ba Mieu Formation was deposited about 176±52 ka during marine isotope stage (MIS) 7–6. The Thu Duc Formation was deposited about 97±27 ka during MIS 5. Both the Ba Mieu and Thu Duc formations are composed of fluvial and tidally influenced coastal deposits. The newly proposed Nhon Trach Formation was originally an eolian (blanket) deposit, but it has been partly reworked by fluvial processes. The Nhon Trach Formation was deposited about 10.9±4.7 ka, in the last part of the Pleistocene to the beginning of the Holocene. The OSL ages for the Ba Mieu, Thu Duc, and Nhon Trach formations are younger than the ages previously assigned to these formations.  相似文献   

Remote sensing parameterization of the processes of energy and water cycle over desertification areas     

Yaoming Ma  Osamu Tsukamoto  Hirohiko Ishikawa 《中国科学D辑(英文版)》2002,45(1):47-53

In order to understand the processes of land surface-atmosphere interaction over desertification area, it is indispensable to utilize of satellite remote sensing. Two scenes of Landsat TM were used to produce a set of maps of surface reflectance, MSAVI, vegetation coverage, surface temperature, net radiation, soil heat flux, sensible heat flux and latent heat flux. Statistical analysis based on these maps revealed some quantitative significant land surface characteristics. Future developments of the method are also discussed.  相似文献