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Volume 45, Issue 7
Displaying 1-7 of 7 articles from this issue
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Edwaxd K. Kazimirovsky, Victor D. Kokourov, Toshitaka Tsuda, Susumu Ka ...1993 Volume 45 Issue 7 Pages 541-546
Published: July 20, 1993
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSObservations of wind fields in the upper mesosphere and lower thermosphere (85-95 km) at Irkutsk, East Siberia (52°N, 104°E), and Shigaraki, near Kyoto, Japan (35°N, 136°E), in 1983-1985 were used to study the behavior of mean winds and solar semidiurnal tides. The meridional mean winds were mostly southward at both sites, but the wind amplitudes in Japan were weaker, except in winter 1983/1984, and autumn 1984 and 1985. The zonal mean winds were generally eastward at both sites, but there were distinct differences in annual and interannual variations. The variations of the amplitudes of semidiurnal tides agreed rather well between the two sites, especially for the zonal component. For the meridional component, the amplitudes of semidiurnal tides were systematically greater in East Siberia. The phases of the zonal component agreed fairly well in summer between the two sites, while they were significantly different in winter months. The results of the comparison could be explained by the latitudinal distributions of thermospheric winds, and partly by possible longitudinal variations in the excitation, propagation and dissipation of atmospheric waves due to climatic differences.View full abstractDownload PDF (16929K) -
M. N. Sasi, B. V. Krishna Murthy1993 Volume 45 Issue 7 Pages 547-561
Published: July 20, 1993
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSMaking use of time series data obtained by M-100B rockets at Trivandrum (8.5°N, 77°E) in August 1976, April 1980 and December 1987, diurnal tidal oscillations of winds and temperatures in the 20-80 km height region are studied. The vertical profiles of tidal components obtained from these observations are compared with the theoretically obtained tidal fields. In general, there is agreement between the observational and theoretical profiles, especially in August 1976 and April 1980. However, there are significant differences between the two in certain height ranges.View full abstractDownload PDF (42968K) -
S. Saroso, T. Iyemori, M. Sugiura1993 Volume 45 Issue 7 Pages 563-572
Published: July 20, 1993
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSThe universal time (UT) variation in the ap index for the years 1932-1956 and 1957-1986 is analyzed. Results are compared with the UT variation in the Dst index and with that in the rate of energy input into the ring current estimated from the Dst index. It is found that the UT variation of the ap index does not agree with that of the Dst index, but is in agreement with the UT variation in the rate of energy input into the ring current. Results on the seasonal variation of the ap index indicate that the UT variation has mostly a minimum around 1030 UT for different seasons, though the average values have features similar to the well-known semiannual variation in geomagnetic activity. The averaged ap values and the numbers of events of the ap greater than 30, 50, or 100 reach a minimum around 1030 UT or during the UT time interval 0900-1200. These values are anti-correlated with the UT variation of the magnetic flux that would occupy the nightside auroral oval approximated by offset circles in corrected geomagnetic coordinate system. The modulation of E × B drift speed in the magnetosphere by the UT variation of the oval magnetic flux could be the source of the UT variation in the ap and the Dst index.View full abstractDownload PDF (27058K) -
J. M. Torta, A. García, A. DE Santis1993 Volume 45 Issue 7 Pages 573-588
Published: July 20, 1993
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSA Spanish Geomagnetic Reference Field for epoch 1990 has been produced using the technique of spherical cap harmonic analysis (SCHA). The data set on which the model is based includes both Magsat and ground (observatory and repeat-station) three-component data. The field data have been updated to 1990 by means of a spherical cap harmonic model of secular variation for a spherical cap of half-angle 16° for the time interval 1970-1989.5. Due to the poor distribution of the ground data (almost entirely restricted to the mainland areas) we have confined the analysis to a smaller cap (8°). Before applying SCHA, field values from the IGRF 1985, evaluated at 1990, were removed from the data and only the residuals were analyzed. We found that the removal of a trend from the satellite residuals improved the fit of the resulting model to the ground data; we also found some difficulties using SCHA to extrapolate Magsat measurements to the ground. Appropriate solutions to this problem are presented. Charts of the elements of the 1990 Spanish Geomagnetic Reference Field (after the addition of the field values computed using the IGRF model) are shown, along with the secular variation maps for that epoch as deduced from the secular variation model.View full abstractDownload PDF (36728K) -
Tsuneji Rikitake1993 Volume 45 Issue 7 Pages 589-594
Published: July 20, 1993
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSElectromagnetic shielding by a spherical shell having a hole is studied relying on the relaxation technique. Unlike the former paper (RIKITAKE, 1992a), the time-dependent magnetic field given to the shell is perpendicular to the direction connecting the shell center to the hole center. Only the shells which are perfectly conducting are studied. The shielding power becomes somewhat smaller than that of an external magnetic field which is parallel to the direction connecting the shell center to the hole center, as studied in the former paper. Similar study of electromagnetic shielding for thin cylindrical shells having a defect is also made in Appendix.View full abstractDownload PDF (13062K) -
Hideaki Otake, Hidefumi Tanaka, Masaru Kono, Kazuo Saito1993 Volume 45 Issue 7 Pages 595-612
Published: July 20, 1993
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSPaleomagnetic studies, both directions and intensities, were made on lavas and dikes of Pleistocene age collected at the Zao Volcano Group, Japan. All the rock units collected have radiometric ages obtained by K-Ar method which cover the last one million years. Among 16 paleodirections obtained after cleaning by alternating field and thermal demagnetizations, eleven belong to the Brunhes chron, four to the Matuyama chron and one probably to the Jaramillo subchron. Angular standard deviation calculated from eleven sites of Brunhes chron was 11.9° with upper and lower 95% confidence limits of 16.8° and 9.2° respectively. This value is not inconsistent with the result from 113 poles in the Brunhes chron for Central Japan, although the confidence interval of our result is too large to assess any regional difference in paleosecular variation. Paleointensity experiment by the Thelliers' method was applied to a total of 70 specimens from nine cooling units. Among them, 31 specimens gave successful results and four and two paleointensities were obtained for the Brunhes and Matuyama chrons, respectively. Some correlations were found between the success rate of paleointensity experiment and reproducibility of the continuous measurements of magnetic susceptibility versus temperature. Such measurement of susceptibility and repeating it stepwisely by increasing the maximum temperature attained is proposed as a preceding technique to select suitable samples for thermal demagnetization and the Thelliers' experiment.View full abstractDownload PDF (49516K) -
T. Terasawa, M. Hoshino, M. Fujimoto1993 Volume 45 Issue 7 Pages 613-618
Published: July 20, 1993
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSFor the steady-state three-dimensional reconnection problem in a compressible plasma, we have found a new class of exact solutions, which consist of ideal-MHD regions, MHD singularities (slow shocks and rotational discontinuities), and a neutral line. This solution predicts the existence of plasma jetting parallel to the neutral line, in addition to the usual plasma jetting in the direction perpendicular to the neutral line. However, contrary to the suggestion by LAu and FINN (1990), and PRIEST and FORBES (1992) that three-dimensional reconnection regions should have velocity singularities, our solution has well-behaved velocity fields without any singularity.View full abstractDownload PDF (16655K)
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