巻号一覧
41 巻, 4 号
選択された号の論文の5件中1～5を表示しています
- |<
- <
- 1
- >
- >|
-
Hiroshi OYA, Masahide IIZIMA, Akira MORIOKA1989 年 41 巻 4 号 p. 331-369
発行日: 1989年
公開日: 2010/09/14
ジャーナル フリーWithin decametric radio emissions from the region near the galactic center, a pulse component has been detected in a frequency range from 25.5 to 29.3MHz, with a period of 421.602msec, and with a power level that is approximately 0.8% of the background random noise level from the Galaxy. The dispersion effect shows that NL=270±30pc/cc where N and L are the electron number density and the distance, respectively; and the Doppler effect on the observed period caused by the orbital motion of the earth also suggests that the source of the pulsating component is located at the galactic center. A rotating super massive black hole at the galactic center is inferred as a candidate for the origin of this pulsating component.抄録全体を表示PDF形式でダウンロード (2902K) -
P. E. SANDHOLT, B. LYBEKK, A. EGELAND, R. NAKAMURA, T. OGUTI1989 年 41 巻 4 号 p. 371-387
発行日: 1989年
公開日: 2010/09/14
ジャーナル フリーGround-based observations of the midday aurora by all-sky TV and meridian scanning photometers reveal the intermittent occurrence of discrete auroral displays within the cusp/cleft. A typical sequence includes the following features: Auroral brightening, near the equatorward boundary of the persistent cusp/cleft arc and subsequent poleward motion of discrete forms through the cusp/cleft region. A strong westward component of auroral motion, both of the individual forms and internal ray structures within these forms, is often observed. At maximum brightness, green line intensities of -10 kilo-rayleighs are observed, even within the interval which is otherwise characterized as the midday gap. The duration of the whole sequence is normally less than 10 minutes. During this period the auroral activity moves poleward, usually by a few degrees, in some cases by 3-5 degrees, say from 71° up to 75° MLAT. Characteristic ground magnetic signatures are observed, including a 50-100nT positive deflection in the H-component and a negative Z-component at stations located poleward of the initial brightening. A poleward propagating filamentary Hall current belt associated with the discrete aurora is inferred from the optical and magnetic data. A quantitative estimate shows that the conductivity enhancement due to electron precipitation in conjunction with northward electric field roughly accounts for the magnetic deflection on the ground. Series of such events are often observed when the cusp is located at rather low latitudes, say south of 75° MLAT, associated with negative IMF Bz.抄録全体を表示PDF形式でダウンロード (3010K) -
Masahiro KODAMA, Koichi OGURA1989 年 41 巻 4 号 p. 389-409
発行日: 1989年
公開日: 2010/09/14
ジャーナル フリーThe purpose of the present paper is to estimate defocusing characteristics of auroral X-ray images observed at balloon altitudes, on the basis of propagation properties of photons from the top to deep in the atmosphere. A Monte Carlo simulation of the X-ray propagation down to a selected atmospheric depth between 6 and 14g/cm2 was carried out to deduce the spatial dispersion of the initial source photons with different functions of energy and incident direction. The simulation results obtained can be summarized as follows: 1) the horizontal dispersion at a depth is amplified with increasing energy and incident zenith angle of source photons; 2) a fractional contribution of the upward scattering photons amounts to about one-third of the downward moving photons; 3) the omni-directional X-ray detector provides the defocusing of ±10-12km at balloon altitudes for any spectral type of isotropic photon; and 4) the collimated detector with a limited field of view reduces the dispersion widths, say ±10° in collimation angle, to about one-third of case 3. An example demonstrates defocused images of a ring-shaped photon source, as functions of incident direction, collimation angle and atmospheric depth.抄録全体を表示PDF形式でダウンロード (1863K) -
Ari VILJANEN, Risto PIRJOLA1989 年 41 巻 4 号 p. 411-420
発行日: 1989年
公開日: 2010/09/14
ジャーナル フリーA method to estimate geomagnetically-induced currents (GICs) in a power grid based directly on magnetic recordings is presented. To determine the electric field on the earth's surface for the calculation of GICs based on available magnetic data, a model is used in which the geomagnetic variation field propagates as a vertical plane wave in the earth and the earth is a half-space with a constant conductivity. To get statistically reliable results, the earth's conductivity is allowed to be a function of the geomagnetic K-index. The reason for this unphysical behaviour, which means that the conductivity is, of course, not real but some kind of an effective conductivity, is explained.抄録全体を表示PDF形式でダウンロード (875K) -
Yukiko YOKOYAMA, Takesi YUKUTAKE1989 年 41 巻 4 号 p. 421-442
発行日: 1989年
公開日: 2010/09/14
ジャーナル フリーIn the dynamo problem, the calculation of induced modes is of vital importance, because the interaction of fluid motions with the magnetic field induces specific types of fields which are, in many cases, different either from the type of velocity field or from the original magnetic field. This special induction relationship, known as “selection rules”, has so far been derived by calculating Adams-Gaunt integrals and Elsasser integrals.
In this paper, we calculate the induced modes in a more direct way, expressing the magnetic fields and the velocity in a spherical harmonic series. By linearizing the product terms of spherical harmonic functions, which appear in interaction terms between the velocity and the magnetic field, into a simple spherical harmonic series, we have derived the induced magnetic modes in a simple general form.
When the magnetic field and the velocity are expressed by toroidal and poloidal modes, four kinds of interaction are conceivable between the velocity and the magnetic field. By each interaction, two modes, the poloidal and toroidal, are induced, except in the interaction of the toroidal velocity with the toroidal magnetic field, which induces only the toroidal mode. In spite of the diversity of interaction processes, the induced modes have been found to be expressed simply by two types. For a velocity of degree l and order k interacting with a magnetic field of degree n and order m, one type is the mode with degree and order of n+l-2t, |m±k| for an integer t, and the other with n+l-2t-1, |m±k|.抄録全体を表示PDF形式でダウンロード (1302K)
- |<
- <
- 1
- >
- >|