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Volume 45, Issue 3
Displaying 1-6 of 6 articles from this issue
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J. Y. Liu, F. T. Berkey1993 Volume 45 Issue 3 Pages 207-217
Published: March 20, 1993
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSApplying perturbation theory to the Appelton-Hartree formulas, a detailed derivation of ionospheric parameters for ionospherically reflected echoes shows that: 1) oscillations of Doppler velocity, virtual height and echo amplitude have the same power spectrum; 2) the temporal variations in Doppler velocity lead or lag those in phase height by 90° and 3) the phase difference between the variations in echo amplitude and those in virtual height is either 0° or 180°. The analysis of experimental data obtained using a digital HF ionosonde (Dynasonde) confirms that oscillations in Doppler velocity, virtual height and echo amplitude have nearly identical power spectra and the phase difference is in good agreement with the derived theory. It is concluded that several different parameters measured by or derived from ionospheric soundings can be used to study ionospheric variations.View full abstractDownload PDF (25736K) -
Hiroshi Amemiya, Yoshiharu Nakamura1993 Volume 45 Issue 3 Pages 219-230
Published: March 20, 1993
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSThe result of observations on the D-layer by the S-310-20 rocket, which was launched from the Kagoshima Space Center (KSC) at 4:30 am in January 28, 1990, is presented. A Faraday cup with a grid and a collector was used to measure the currents of charged particles of both signs. The saturation currents at positive and negative biases are found to be of a comparable order up to 85 km. It is deduced from the data analysis by considering the rocket velocity and precession that in the D-layer the ratio of the negative to the positive ion density is 80-88% at heights lower than 82 km and decreases with height above 82 km toward the E-layer. The effective negative ion density is nearly constant below 74 km, increases from 102 to 103 cm-3 toward 85 km, and then decreases toward the E-layer.View full abstractDownload PDF (27923K) -
T. Oguti1993 Volume 45 Issue 3 Pages 231-242
Published: March 20, 1993
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSVariations in the location of the auroral zone over the past 1000 years is inferred from a model of secular variation in the geomagnetic field and its backward extrapolation. It is shown that the auroral zone was elongated and deviated towards the European sector 300 years ago, although it is deviated to the Canadian sector at present. The northern UK was located in or very close to the auroral zone, and large parts of the UK, Denmark and northern Germany were in the subauroral zone at that time. It cannot be accidental that the studies of aurorae were developed in France and the UK in the 17th and 18th centuries.View full abstractDownload PDF (31321K) -
J. Urrutia-Fucugauchi, J. O. Campos-Enriques1993 Volume 45 Issue 3 Pages 243-249
Published: March 20, 1993
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSObservatory data for temporal variations of the geomagnetic field in central Mexico are analyzed for the period since 1923 AD. Annual mean values of the intensity have decreased from 46, 076 nT to 42, 832 nT at a linear-regression rate of about 48 nT per year. The geomagnetic field direction has been varying from easterly to westerly declinations and towards steeper inclinations. During an early interval from 1923 to 1938, changes were mainly in inclination, this was followed by a brief period with low directional change from about 1938 to 1942, and since 1942, changes have been mainly in declination. Comparison of the observatory data with IGRF models for the period 1945 to 1990 shows that IGRF provides an excellent estimation of the geomagnetic parameters in this low latitude region (19.7°N). In particular this comparison study supports the existence in central Mexico of a relatively small secular variation as implied by the IGRF and observatory data.View full abstractDownload PDF (14040K) -
P. F. Chen, P. C. W. Fung1993 Volume 45 Issue 3 Pages 251-259
Published: March 20, 1993
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSA strong earthquake of magnitude 7.6 occurred on November 15, 1986 near Hualian. The Lunping geomagnetic observatory in the Taiwan region is situated 110 km from the epicentre of the strong earthquake. In this study, the geomagnetic data of the Lunping observatory from 1970 to 1988 are utilized for computing the geomagnetic transfer functions. Our results show that the remarkable time changes in Au, the real part of the transfer function A, appear to be related to the occurrence of the 1986 earthquake. The magnitudes of Au, for the periods of 31, 25, 21 and 14 min decreased gradually from 1970 to 1985 and partially recovered in 1986 before the earthquake occurrence. After the earthquake occurrence the magnitudes of Au decreased again. No significant variation was detected in the time changes of Av, Bu and Bv within the error levels. In other words, the real Parkinson arrow rotated clockwise towards the earthquake region in the interval of 1970 to 1985. We consider that the variation of the real Parkinson arrow might be ascribed to the elevation of the top level of a conductivity anomaly, which is deeply buried at the south-east side of the Lunping observatory. We propose that this elevation might be related to the preparation process of strong earthquake. Besides, it is worth pointing out that the noticeable annual change rate in Au, is up to 0.01 before the 1986 Hualian earthquake; such a change rate is comparable to that detected at Kakioka before the 1923 Kanto earthquake.View full abstractDownload PDF (21495K) -
Kazuo Saito1993 Volume 45 Issue 3 Pages 261-272
Published: March 20, 1993
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESS40Ar/39Ar analyses on hornblende and biotite samples separated from the Tanzawa tonalite demonstrate that most samples have highly disturbed K-Ar systematics. Expect for Mt. Ishiwari samples, unrealistically old ages are commonly observed in lower temperature fractions. Especially, Omatazawa samples showed severely disturbed age spectra, which strongly suggests that one should not use the previously reported 10 Ma hornblende K-Ar ages in the southwestern margin of the Tanzawa pluton in a discussion of the cooling history of the pluton. In the eastern part, although showing a clear evidence of excess argon in the lower temperature fractions, the biotite and hornblende in the Yushin sample yield poorly defined high temperature plateaus about 5 Ma. On the other hand, the biotite and hornblende separated from the Mt. Ishiwari sample reveal apparently good plateaus in age spectra. However, the biotite has a plateau age older than that for the cogenetic hornblende, which is consistent with our previous K-Ar results on these samples, but is inconsistent with the widely accepted closure temperature hypothesis. Comparing with our previous K-Ar results, the 6.26 +/- 0.17 plateau age for the hornblende could be interpreted as the time when the sample cooled to the closure temperature of hornblende (about 500°C). The older age of the biotite should be due to excess argon.View full abstractDownload PDF (23817K)
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