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   

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   

The sudden disappearance of a dark filament observed on October 26, 1989     

Jun Kubota  Reizaburo Kitai  Ichiro Tohmura  Akira Uesugi 《Solar physics》1992,139(1):65-79

We present H monochromatic and spectroscopic observations of the sudden disappearance of a dark filament located near the center of the solar disk on October 26, 1989. The event was not associated with the flare activity. The dark filament first disintegrated into two loop-like components, and then each component successively showed ascending motion with a velocity greater than 30 km s^–1. Comparison of the H pictures taken before and after the start of this event suggests that the dark filament was originally composed of two magnetic flux loops.  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   

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   

Gelifluction within a solifluction lobe in the Kärkevagge valley, Swedish Lapland     

Hotaka Matsumoto  & Mamoru Ishikawa 《Geografiska Annaler: Series A, Physical Geography》2002,84(3&4):261-266

Soil displacement, soil temperature, depths of thaw plane and groundwater level were continuously monitored during the period from July 1999 to June 2000 within a solifluction lobe in the Kärkevagge valley, northern Sweden. The strain–probe method was used to measure soil displacement, and we found significant soil displacements in the thawing period 2000. These displacements were the result of gelifluction. The ice content profile showed that gelifluction occurred at the same time as the thaw plane reached the layers with high ice content at shallow soil depths (0–6 and 16–25 cm deep). In contrast, gelifluction did not occur when the thaw plane reached the layers with high ice content at greater depth (46–49 cm deep). These observations indicate that thawing of ice lenses in the near–surface layer triggers gelifluction.  相似文献   

Analysis of crack movements observed in an alpine bedrock cliff     

Mamoru Ishikawa  Yoshimasa Kurashige  Kazuomi Hirakawa 《地球表面变化过程与地形》2004,29(7):883-891

Crack widths and rock temperatures were monitored on an andestic bedrock cliff in the summit area of the Daisetsu Mountains, Hokkaido, northern Japan. Sequential data recorded the gradual widening of a crack to the point of critical crack extension, which resulted in catastrophic rock breakage. The data indicate that a combination of liquid water in?ltration into crack tip and subsequent freezing is the most signi?cant factor contributing to critical crack extension. The recorded sub‐critical crack movements involved a number of minor crack extensions and contractions, the timing of which correlates well with the magnitude of the reconstructed thermal stresses at the crack tip derived from thermal deformation of the plate‐shaped rock fragment. Larger crack extensions occurred when stress at the crack tip exceeded a threshold value, possibly re?ecting the control of rock fracture mechanics by which cracks are thought to propagate when the stress intensity factor at the crack tip exceeds the threshold values for stress corrosion cracking and the fracture toughness of the material. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

Effects of mass source/sink at the western boundary on the wind-driven gyres: Implications for the ventilation of the north pacific intermediate layer through convection in the Okhotsk Sea and tidal mixing at the Kuril Straits     

Tomohiro Nakamura  Takahiro Toyoda  Yoichi Ishikawa  Toshiyuki Awaji 《Journal of Oceanography》2010,66(1):41-60

A steady quasi-geostrophic 2.5-layer model, forced by both Ekman pumping and a mass source/sink situated at the western boundary has been constructed to investigate the effect of diapycnal transport due to convection in the Okhotsk Sea and tidal mixing at the Kuril Straits on the intermediate layer in the North Pacific. The model illustrates a combined effect of the wind-driven and mass-driven circulations. First, net mass input induces a “barotropic” mode inter-gyre flow along the western boundary through the dynamical influence of Kelvin waves. This flow creates characteristic curves (geostrophic contours) that facilitate inter-gyre communication through the western boundary layer from the location of the mass source to the subtropical gyre. Due to the effect of wind-driven circulation, the offshore part turns eastward into the interior, encircles the outer rim of the region (which would otherwise be the pool region in the absence of mass input), and then encounters the western boundary. Eventually, the water fed into the lower layer flows mostly along this path and later flows away to the equatorial region. Conversely, in the upper layer, water is fed from the equator to the subtropics, and to the subpolar interior region through the western boundary current. The water then circulates along the outer rim and is absorbed into the mass sink. The model is controlled mainly by three nondimensional parameters: (1) the ratio of net mass input rate to the maximum Sverdrup transport (Q/T _Sv ^max ), which affects the inter-gyre communication by altering the paths of geostrophic contours, (2) the ratio of a mass input rate into the lower layer to that in total (Q ₂/Q), which controls the vertical structure of the inter-gyre flow, and (3) the measure of the wind forcing effect relative to the β effect, which determines the horizontal extent of the area influenced by the mass input. The other parameter regimes with respect to Q/T _Sv ^max and Q ₂/Q are also presented.  相似文献   

Nucleation,growth and stability of CaAl2Si2O8 polymorphs     

Toshiya Abe  Katsuo sukamoto  Ichiro Sunagawa 《Physics and Chemistry of Minerals》1991,17(6):473-484

By means of in situ observation, the nucleation and growth of triclinic, pseudo-orthorhombic and pseudo-hexagonal CaAl₂Si₂O₈ were investigated and their relative stabilities established. Pseudo-hexagonal and pseudo-orthorhombic CaAl₂Si₂O₈ nucleate prior to anorthite and grow in a supercooled anorthite melt before the latter appears. They either dissolve or transform to anorthite once the latter nucleates and starts to grow. Corundum and mullite also nucleate metastably prior to anorthite in this melt. The liquidus temperatures of the four metastably nucleated phases were determined precisely by in situ measurements of the transformation temperatures from a polyhedral to a rounded morphology. On the basis of the supercooling thus determined, the growth rate versus supercooling relations were measured and analysed for the respective phases. The growth rate of the stable phase is one order of magnitude higher than those of any metastable phases. However, the growth rates of the three CaAl₂Si₂O₈ polymorphs normalized by the viscosities are nearly the same.  相似文献   

Radiation induced lattice defects in natural zircon (ZrSiO4) observed at atomic resolution     

Keiji Yada  Takayoshi Tanji  Ichiro Sunagawa 《Physics and Chemistry of Minerals》1987,14(3):197-204

Fission tracks and point defects in natural zircon are directly observed by a 1 MV electron microscope at atomic resolution for three types of samples adjusted to the 100 orientation. Lattice planes intersecting the fission tracks at high angles are distorted in a rather irregular manner over a wide region up to more than 100 Å wide. Diameter of the tracks, ranging from 25 Å to 40Å, is much narrower than those so far reported for the U-doped synthetic zircon (100–200 Å), UO₂ thin film (100 Å), mica (66 Å, 240 Å) or fluorophlogopite (150 Å). The fact that fairly long tracks thousands of angstroms in length are observed in thin 100-oriented sample hundreds of angstroms in thickness and that some of them are nearly parallel to a low index lattice plane suggest a possible occurrence of channelling in the process of track formation. Parallel tracks often observed in chemically etched specimens support the idea of channelling. Slightly bent tracks are sometimes observed. It is concluded from computer simulation that many contrast anomalies of bright and dark spots in the lattice image are due to point defects of vacancies and interstitial atoms, mainly produced by the direct atomic collision with α-particles or by passage of ionizing nuclear particles. Optimum conditions of the observation of point defects with highest contrast are studied. One interstitial Zr atom or one Zr ion vacancy will give very low contrast and will be not detectable unless the crystal is less than two unit cells thick. A pair of Zr ion vacancies, however, yields extended detectable limit of thickness. Some of the observed defects are in good accordance with those simulated.  相似文献