A simulation study of the solar wind including the solar rotation effect

An axisymmetric solar wind structure including the solar rotation effect is studied by the method of MHD computer simulation. For the case of the radial magnetic field configuration, the simulation result is fairly well coincident with the steady-state solution. For the case of the dipole magnetic field configuration, the properties of the solution depend on the ratio of the gas pressure to the magnetic pressure-ratio) in the model. If the-ratio is small, a clearly defined stagnation region appears in the wind, in which the flow speed is very small and the azimuthal magnetic field is very weak because of the corotation of the plasma. If the-ratio is greater than 1, the plasma is not effectively trapped by the magnetic field so that the stagnation region is not clearly defined in the solution.     

Feeding Habits of the Mesopelagic Fish Gonostoma gracile in the Northwestern North Pacific

The diet of Gonostoma gracile, a numerically abundant mesopelagic fish in the Subtropical Region and the Transition Domain of the northwestern North Pacific, was examined using 520 specimens collected during June–July 1988, June 1995 and November 1995. The prey included mainly copepods, ostracods, amphipods and euphausiids. Copepods and ostracods were the most abundant, comprising approximately 70% of the total diet. There was little evidence of an ontogenetic dietary shift; Pleuromamma copepods were the most abundant prey for all size classes of fish ranging from 19 to 116 mm in standard length. The size range of prey increased with growth, but all fish sizes examined fed mainly on 1–4 mm long prey. Luminescent copepods and ostracods were the most abundant prey, suggesting that G. gracile detects its prey visually. This revised version was published online in August 2006 with corrections to the Cover Date.     

Influence functions for stress and displacement discontinuity elements in an anisotropic medium

Influence functions, that permit us to determine stresses and displacements at an arbitrary point in an infinite, homogeneous, linear elastic, anisotropic medium due to different three-dimensional (3-D) stress or displacement discontinuities distributed on infinite, flat, band-type elements, are presented. Any straight-line segment on the band, which is perpendicular to its infinite side, has the same distribution of the discontinuities. Along with the functions, their Taylor series approximations are also provided. The last can be useful to analyse stresses and displacements at points distant from the elements. The functions allow us to avoid procedures of numerical integration in the Indirect Boundary Element Method and/or the Displacement Discontinuity Method computer codes that are able to solve complete plane-strain problems with 3-D boundary conditions for an elastic, anisotropic medium. © 1997 by John Wiley & Sons, Ltd.     

Topology of Magnetic Field and Coronal Heating in Solar Active Regions – II. The Role of Quasi-Separatrix Layers

The photospheric vector magnetic fields, H and soft X-ray images of AR 7321 were simultaneously observed with the Solar Flare Telescope at Mitaka and the Soft X-ray Telescope of Yohkoh on October 26, 1992, when there was no important activity in this region. Taking the observed photospheric vector magnetic fields as the boundary condition, 3D magnetic fields above the photosphere were computed with a new numerical technique. Then quasi-separatrix layers (QSLs), i.e., regions where 3D magnetic reconnection takes place, were determined in the computed 3D magnetic fields. Since Yohkoh data and Mitaka data were obtained in well-arranged time sequences during the day, the evolution of 3D fields, H features and soft X-ray features in this region can be studied in detail. Through a comparison among the 3D magnetic fields, H features and soft X-ray features, the following results have been obtained: (a) H plages are associated with the portions of QSLs in the chromosphere; (b) diffuse coronal features (DCFs) and bright coronal features (BCFs) are morphologically confined by the coronal linkage of the field lines related to the QSLs; (c) BCFs are associated with a part of the magnetic field lines related to the QSLs. These results suggest that as the likely places where energy release may occur by 3D magnetic reconnection, QSLs play an important role in the chromospheric and coronal heating in this active region.     

A possible method of accelerating relativistic electrons in the neutral sheet in the Jovian outer magnetosphere

It is suggested that the periodic modulation of Mev electron fluxes observed by Pioneer 10 in its outbound orbit was due to crossing the magnetically neutral sheet in the Jovian outer magnetosphere. It is pointed out that these electrons are continually generated in this sheet formed in the outer magnetosphere beyond about 20 Jupiter radii from the planet.     

A study of magnetic energy build-up based on vector magnetograms

Solar Physics - Vector magnetograms taken at the Okayama Astrophysical Observatory are studied. A sequence of procedures applied to the data for analysis are explained, and their validity is...     

Short-Range Prediction Experiments with Operational Data Assimilation System for the Kuroshio South of Japan

The short-range (one month) variability of the Kuroshio path was predicted in 84 experiments (90-day predictions) using a model in an operational data assimilation system based on data from 1993 to 1999. The predictions started from an initial condition or members of a set of initial conditions, obtained in a reanalysis experiment. The predictions represent the transition from straight to meander of the Kuroshio path, and the results have been analyzed according to previously proposed mechanisms of the transition with eddy propagation and interaction acting as a trigger of the meander and self-sustained oscillation. The reanalysis shows that the meander evolves due to eddy activity. Simulation (no assimilation) shows no meander state, even with the same atmospheric forcing as the prediction. It is suggested therefore that the initial condition contains information on the meander and the system can represent the evolution. Mean (standard deviation) values of the axis error for all 84 cases are 13, 17, and 20 (10, 10, and 12) km, in 138.5°E, in the 30-, 60-, and 90-day predictions respectively. The observed mean deviation from seasonal variation is 30 km. The predictive limit of the system is thus about 80 days. The time scale of the limit depends on which stage in the transition is adopted as the initial condition. The gradual decrease of the amplitude in a stage from meander to straight paths is also predicted. The predictive limit is about 20 days, which is shorter than the prediction of the opposite transition. This revised version was published online in July 2006 with corrections to the Cover Date.     

Global instability of thin stellar discs

We have determined the dominant global modes of stellar discs by integrating the linearized collisionless Boltzmann equation. The models examined are the Kuzmin discs with two types of the distribution function. It is found that the growth rate correlates well with the central value ofQ.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.     

Computed magnetic field structure of the flares observed by Hinotori hard X-ray telescope

Potential field computations have been carried out to study the location of hard X-ray sources observed by the HINOTORI hard X-ray imaging instrument, SXT. Of the two flares studied, the X-ray source of the 1981 May 13 event, a very unusual gradual flare, appears to lie at the top of an arcade of field lines. In the other event, the 1981 October 15 flare, the observed double source structure is not explained in the present computation, implying the existence of non-negligible electric currents in the flare region.