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Volume 46, Issue 3
Displaying 1-9 of 9 articles from this issue
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Takashi Watanabe, Takashi Kikuchi1994 Volume 46 Issue 3 Pages 169
Published: March 20, 1994
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSDownload PDF (125K) -
N. Fukushima, Y. Kamide1994 Volume 46 Issue 3 Pages 171-176
Published: March 20, 1994
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSDuring the severe magnetic storm on October 21, 1989, three intense substorms took place successively at 2-hour intervals in evening-midnight hours in the Western Pacific region, with the sense of (ΔD, ΔH) deviations of three geomagnetic bays associated with the substorms being (+, -), (+, + to -, +), and (-, +), respectively. The second and third bays were observed in conjunction with an unusual low-latitude aurora seen in the northern sky of Hokkaido (the northern island of Japan). In this paper, a scenario is proposed for the occurrence mechanism of these three consecutive bays, in which they are accounted for in terms not only of a local increase in the Hall conductivity in the ionospheric E-layer but also of a decrease in the Pedersen conductivity in the F-layer. A noticeable upward drift of the F-layer associated with the low-latitude aurora is responsible for the reduction of the Pedersen conductivity, despite an increase in the total electron content in the ionosphere.View full abstractDownload PDF (1119K) -
Yoshihiro Higuchi1994 Volume 46 Issue 3 Pages 177-192
Published: March 20, 1994
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSIrregular magnetic pulsations and IPDP plasma wave events related to the low latitude aurora were observed at Yonezawa observatory on October 20 and 21, 1989. Three positive bays appeared in the magnetograms on October 20. Concurrently, IPDP, Pi 2, Pi B and Pi C are registered during the respective positive bays. The power spectrum estimations of irregular magnetic pulsations are carried out by the maximum entropy method indicating that the spectral peaks are mainly distributed in the frequency band between 0.1 Hz and 0.2 Hz. When the magnetopause is compressed by a sudden increase of the solar wind pressure inside the geosynchronous orbit, transient magnetic field oscillations are observed on the ground. Two distinct positive bays at the time of the minimum H during the main phase of the geomagnetic storm occurred in the magnetograms on October 21. The irregular magnetic pulsations accompanying the IPDP plasma wave events and the low latitude optical aurora were observed during each positive bays.View full abstractDownload PDF (3256K) -
M. Nishino, Y. Tanaka1994 Volume 46 Issue 3 Pages 193-203
Published: March 20, 1994
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSLow-latitude VLF hiss was observed at dawn time at Moshiri (L = 1.6) and Kagoshima (L = 1.2), Japan during 20h00m UT to 23h30m UT on October 20, associated with the severe magnetic storm (Kp = 8) during October 19-21, 1989. The VLF hiss with a band-limited spectrum exhibited an increase of frequency (fmax) of the maximum energy with local time. Based on the quasi-linear model for hiss-type mid-latitude VLF emissions developed by SAZHIN (1984) and using electron density data by EXOS-D satellite, it is estimated that injected electrons of about 5 keV associated with the maximum depression of the magnetic H-component around 13h30m UT on October 20 contribute to the generation of the VLF hiss at dawn time around L = 4.8 of the magnetospheric equatorial region. The plasmapause has been disrupted due to the strong magnetospheric disturbances when the VLF hiss was observed. The increase of fmax may be due to a combined effect of the energy dependences of different drift starting longitudes of the hot electrons injected in the evening sector and of the drift velocities of the electrons encircling the Earth, and a temporal variation of the cold electron density in the generation region at dawn sector. Furthermore it is implied that the VLF hiss has penetrated through the ionosphere at the higher latitude than that of Moshiri and then propagated toward the low-latitude stations in the Earth-ionosphere wave-guide mode.View full abstractDownload PDF (2187K) -
T. Ichinose, T. Ohta, T. Ogawa1994 Volume 46 Issue 3 Pages 205-212
Published: March 20, 1994
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSNot only ionospheric variations observed by HF Doppler method at a well-known low-latitude auroral events but also the associated horizontal electric field estimated from the HF Doppler data, are presented in this paper. Time variation of the horizontal electric field is derived by using the same method of Tsutsui et al. taking into account the effect of electron decay for isolated substorm. In Hokkaido, aurora was observed by photometric means during the time periods of both 1136-1230 and 1415-1420 UT. A clear ionospheric variation of JJY wave signal was recorded during 1136-1230 UT only. It is concluded from the calculated time variation of horizontal electric field that a very strong substorm beginning around 1200 UT may considerably influence the ionosphere. It is very likely that the strong electric field originating from high latitudes can propagate down to lower ionosphere, around the reflection height of JJY waves.View full abstractDownload PDF (1196K) -
K. Yumoto, K. Shiokawa, T. Endo, Y. Tanaka, T. Oguti, F. W. Menk1994 Volume 46 Issue 3 Pages 213-229
Published: March 20, 1994
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSOptical and magnetic observations at the Moshiri Observatory (L = 1.6) of the Solar-Terrestrial Environment Laboratory, Nagoya University, show that invisible low-latitude aurorae sometimes appear in concert with ≥50-nT H component positive magnetic excursions and large-amplitude Pi pulsations during the main phase of magnetic storms, for example, on February 9, 26, 27, and 29 and May 10, 1992, even with a minimum Dst index of only ∼-130 nT. Magnetograms from the L = 1.03-2.13 stations of the 210° magnetic meridian show that the positive excursions in ΔH begin almost simultaneously in the northern and southern hemispheres during the low-latitude aurorae. However, there is large northern-southern asymmetry in the D component magnetic variations during the low-latitude amoral events. The D component magnetic perturbations localized around L = 2 in the southern hemisphere are nearly time derivative of the H component; that is, a bipolar structure. The H and D component magnetic variations have apparent phase delays. The equivalent ionospheric current pattern moves from the midnight side toward the evening and morning sides during the premidnight and postmidnight sectors, respectively. The apparent longitudinal velocity of the equivalent ionospheric current pattern is about 7 km/s at around 40° magnetic latitude. Equivalent ionospheric current vectors deduced from the magnetic variations on the ground in the southern hemisphere show a vortex structure with clockwise rotation. These magnetic variations suggest that an ionospheric Hall current vortex, in which a field-aligned current of 1.4 x 10-8 A/m2 flows upward, must be formed locally near the low-latitude aurorae.View full abstractDownload PDF (3520K) -
K. Shiokawa, K. Yumoto, Y. Tanaka, T. Oguti, Y. Kiyama1994 Volume 46 Issue 3 Pages 231-252
Published: March 20, 1994
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSThis paper reports latitudinal and longitudinal movements of four low-latitude auroras observed by a meridian scanning photometer and an all-sky TV camera at Moshiri and Rikubetsu (L = 1.6) in Japan during magnetic storms. It is observationally found that the low-latitude auroras occur in the region of L ∼ 2 even during moderate magnetic storms. The auroras which are characterized by 6300-Å emissions of several kR are also found to take place associated with magnetospheric substorm activity during the maximum phase of magnetic storms. The auroras and associated current systems inferred from ground magnetic field fluctuations tend to expand from midnight toward both the dawnside and the duskside. It is suggested that the observed low-latitude auroras are excited by precipitating low-energy electrons originated in the plasmasphere. We discuss generation mechanisms of these electrons based on the observations.View full abstractDownload PDF (3793K) -
Bun-iti Saito, Yositaka Kiyama, Tosiyasu Takahasi1994 Volume 46 Issue 3 Pages 253-262
Published: March 20, 1994
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSSpectral characteristics of auroral displays seen from Japan are discussed. A spatially extended low-latitude aurora of February 11, 1958, showed three spectroscopic components having different energy sources; (1) the “central part excitation” of the red doublet of [OI]6300 Å and 6364 Å, which is caused by low energy secondary electrons, (2) the “high-latitude auroral display” of [OI]5577 Å and N2+lN3914 Å lines which is a counterpart of a typical high-latitude aurora, and (3) the “enhanced-airglow” of the N2+1N3914 Å lines which is caused by the diffused energy loss process of precipitating energetic particles. A weak photographic auroral display which was observed in the northern region of Japan on May 10, 1992 also showed similar spectral characteristics to those of the extended event. This suggests that weak auroral events observed from Japan were produced by excitation due to low-energy electrons and the direct excitation due to incoming particles.View full abstractDownload PDF (1548K) -
Shigeyuki Minami1994 Volume 46 Issue 3 Pages 263-270
Published: March 20, 1994
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSWe have made an interpretation of the cause of low latitude aurora event based on our laboratory result of the magnetosphere. The latitudinal change of auroral oval for the different solar wind parameters is investigated. To confirm the validity of the scaling of the laboratory simulation, an analysis of satellite data of the magnetopause stand-off distance dependence on the IMF Bz, is used. The scaling of the magnetic field proved the exact scaling of the experimental IMF value to the real value. The latitude of auroral oval can be obtained from photographs by illumination. The latitude of auroral oval in the night region dependence on the IMF Bz, is obtained. The result shows that the auroral oval latitude of almost 50 degrees in the night region is obtained for Bz = -10 nT. The other investigation is made for the latitudinal dependence of the auroral oval on the solar wind dynamic pressure. The result shows that the latitude becomes to be low when the dynamic pressure is high. During the change of dynamic pressure, other parameters such as Bz are fixed. The result also indicates a possibility of the cause of low latitude aurora for northward IMF. The observed events shows, however, the necessity of the creation of high energy auroral particles. For this meaning, the condition to cause the low latitude aurora events is pointed out showing the important role of the absolute value and the temporal change of the solar wind dynamic pressure.View full abstractDownload PDF (1271K)
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