巻号一覧
41 巻, 7 号
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Masashi HAYAKAWA1989 年 41 巻 7 号 p. 573-595
発行日: 1989年
公開日: 2010/09/14
ジャーナル フリーVLF data from the low-altitude Ariel 4 satellite are used to investigate the characteristics and generation (propagation) mechanism of low- and equatorial-latitude VLF radio noises. Low-latitude emissions are defined as VLF noises whose mean (running mean during -30 sec) intensity exceeds 40 dB above 4.8×10-19W m-2 Hz-1(free space equivalent) at the frequency of 3.2kHz (Δf=1kHz) in each 28sec sampling interval in the magnetic latitude range less than 30°. Three months' data (December 11, 1971 to March 19, 1972) have been used to obtain a full local time coverage. It is then found that the noises are impulsive at that frequency as based on the high values of the observed mean/minimum and peak/mean ratios, and also that they are localized to the longitudes of thunderstorm centers. Hence, low-latitude VLF emissions, as observed in the southern hemisphere for our season, have been found to be well explained by the propagation of sferics to the lowaltitude satellite as short-fractional-hop whistlers; those observed in the northern hemisphere are attributed to the interhemisphere propagation of those sferics in the whistler mode. Furthermore, diurnal variations of the occurrence rate, intensity, spectral property and occurrence latitude are studied, and many of these characteristics are found to be compatible with the ionospheric D-region absorption of whistler-mode propagation in the southern hemisphere. Finally, the satellite VLF data as presented here are suggested as being useful for the study of the global distribution of lightning activity.抄録全体を表示PDF形式でダウンロード (1839K) -
T. SARYO, M. TAKEDA, T. ARAKI, T. SATO, T. TSUDA, S. FUKAO, S. KATO1989 年 41 巻 7 号 p. 597-611
発行日: 1989年
公開日: 2010/09/14
ジャーナル フリーBy using MU radar at Shigaraki, Japan, ion drift and the electron density profile in the F region were observed during two periods, September 17-18 and October 7-8, 1986. Between 23h LT and 24h LT on September 17, a clear difference was found between the electron density profiles observed by the eastward and westward beams, which may be caused by a wave propagated from east to west. A clear negative correlation between the perpendicular northward (V⊥) and parallel (V//) component of the velocity, which is caused by the F region dynamo action, was found as observed at Arecibo. The daily variation pattern of V⊥ was similar to that observed at Arecibo, especially in the daytime, but that of the eastward drift was different. Geomagnetic field variations were estimated by using a drift velocity and conductivities deduced from the IRI 79 model (IRI 79, 1981) compared to observations at Miyazu, approximately 110km northwest of the radar site. Discordance between the estimated and observed field variations was concluded to be caused by ionospheric winds, which contribute to the generation of the geomagnetic Sq field through the induced electric field.抄録全体を表示PDF形式でダウンロード (1164K) -
Y. IWASAKA, Y. MORITA1989 年 41 巻 7 号 p. 613-626
発行日: 1989年
公開日: 2010/09/14
ジャーナル フリーBalloon measurements on stratospheric aerosol made at Syowa Station, Antarctica in 1983 and 1985 suggested a volcanic effect of the El Chichón eruption of 1982 on the Antarctic stratosphere in 1983. The measurements in October 1983 and 1985 showed that the “year to year” cooling of the spring stratosphere also influenced the stratospheric aerosol content. Size distributions measured in the early winter of 1983 and 1985 indicated that fine particle formation was one possible process forming the winter enhancement of stratospheric aerosols (Polar Stratospheric Clouds, PSCs), in addition to the growth of preexisting particles.抄録全体を表示PDF形式でダウンロード (1306K) -
Marianne MARESCHAL, Christian CATELAND1989 年 41 巻 7 号 p. 627-641
発行日: 1989年
公開日: 2010/09/14
ジャーナル フリーThe algorithm developed at the Centre Géologique et Geophysique of Montpellier for the linear inversion of 1-D magnetotelluric observations is briefly presented. It is based on the decomposition of the sensitivity matrix in singular values. The effect of unimportant parameters is damped in the manner proposed by MARQUARDT (1963). Our damping factor is first set equal to the smallest eigenvalue and progressively increased up to a maximum preset value if this is needed to insure convergence of the iterative scheme. The algorithm is shown to perform quite well in terms of computer time and minimization of misfit when compared to the scheme of FISCHER and LE QUANG (1981). After a variety of tests on synthetic and field data, including those selected for the COPROD experiment, it is applied to a set of noisy data that are certainly not strictly 1-D. The eigensolution analysis proves to be very useful in providing a 1-D pseudo section later used as reference for the definition of more realistic 2- or 3-D models of the region (MARESCHAL and CHOUTEAU, 1989).抄録全体を表示PDF形式でダウンロード (1389K) -
Masahiko TAKEDA1989 年 41 巻 7 号 p. 643-646
発行日: 1989年
公開日: 2010/09/14
ジャーナル フリーThe amplitude ratio and phase difference of the spherical harmonics of the magnetic potential between the internal and external parts of the geomagnetic Sq field are obtained at every hour of universal time from March 1-20, 1980. It is found that the phase difference in the P21 mode is small when the external current vortex is above the Pacific Ocean. This suggests a significant effect of the currents induced in the ocean. The phase difference in the P32 mode shows an irregular UT variation pattern. This is perhaps caused by the effect of the internal P32, or higher mode magnetic field, induced in the inhomogeneously distributed oceans by the external P21 mode, which has the largest amplitude.抄録全体を表示PDF形式でダウンロード (387K)
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