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Volume 48, Issue 3
Displaying 1-12 of 12 articles from this issue
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H. Oya1996 Volume 48 Issue 3 Pages 257
Published: March 20, 1996
Released on J-STAGE: May 25, 2007
JOURNAL FREE ACCESSDownload PDF (138K) -
Cornelis DE Jager1996 Volume 48 Issue 3 Pages 259-271
Published: March 20, 1996
Released on J-STAGE: May 25, 2007
JOURNAL FREE ACCESSSolar flares consist of two broad groups: the compact and the eruptive ones. The first develop in complicated magnetic environments close to sunspots; the others are larger, and extend farther from spots. The recent YOHKOH observations have shown the close correlation between the ignition of compact flares and flux tube interaction or instability. There is also evidence that the interaction in a compact flare is not a single act but that it occurs repeatedly. The eruptive flares are related to prominence instability. Since they extend higher up in the corona in a fairly open field-line configuration, their correlation with particle or plasma cloud ejection is stronger than for compact flares. We advance arguments that particle acceleration in a fully developed flare consist of three phases: the first occurs in an e.m. field originating during the current-loop interaction or the loop instability, the second occurs in the shockwave field that develops immediately after that phase and the third one happens in the shock-wave field that originates higher-up in the corona after the flare.View full abstractDownload PDF (3563K) -
F. S. Wet, H. Y. Liu1996 Volume 48 Issue 3 Pages 273-277
Published: March 20, 1996
Released on J-STAGE: May 25, 2007
JOURNAL FREE ACCESSThis paper presents the numerical simulation of the evolution of shock wave propagating through the magnetic helmet streamer region and further out along the current sheet. It was obtained by using a set of complete projected-characteristic boundary conditions at the inner (1.1 Rs) and outer (62 Rs) boundaries in the solarmeridian. Mainresults reveal that (1) the convection effect of the background wind speed on the propagation of shock wave is significant, especially in the range of ≤60 Rs; (2) a dip of flow speed is formed in the magnetic helmet region and after that, it is weakened in the current sheet region; (3) two high-speed belts appear near the two sides of the magnetic helmet when this is stretched outward; (4) a high-density ring displaces behind the shock surface and could be torn when it moves from the magnetic helmet into the current sheet region.View full abstractDownload PDF (861K) -
Yutaka Uchida1996 Volume 48 Issue 3 Pages 279-290
Published: March 20, 1996
Released on J-STAGE: May 25, 2007
JOURNAL FREE ACCESSIn the present paper, we discuss some results of the observation on the dynamical phenomena in the inner corona by Yohkoh. Highly dynamical behavior of the corona revealed by Yohkoh consists of (a) reconfiguration of an extended region of the background corona in association with a small brightening in active region, (b) heated mass ejection into surrounding magnetic field structures (so-called X-ray jets are those in the case of open field regions), and (c) arcade formation above the field-polarity-reversal-lines in the photosphere, both inside active regions (arcade type X-ray flares) and outside active regions (fainter X-ray arcade formation), sometimes in the circumpolar regions very far from active latitude belts. We suggest some possible new interpretations where previously considered models do not seem to be suitable in explaining the new findings.View full abstractDownload PDF (3022K) -
F. S. Wei, S. Q. Liu1996 Volume 48 Issue 3 Pages 291-297
Published: March 20, 1996
Released on J-STAGE: May 25, 2007
JOURNAL FREE ACCESSBased on 297 interplanetary shock waves and corresponding geomagnetic disturbances, the relation between their structures has been studied. For the case in which the interplanetary magnetic field lies basically in the ecliptic plane, we found that (1) the temporal profile of geomagnetic disturbance is mainly determined by the plasma state of the shock waves, especially, the closed relation exists between the plasma temperature profile and the recovery phase of geomagnetic disturbances; (2) shock wave energy transfer index, Fs, as defined in the paper, can give a good prediction of the temporal profiles of geomagnetic disturbances. Thus, it may be deduced that there is a basic energy transfer mechanism associated with plasma processes, which would control geomagnetic disturbance profiles, when a southward-component of interplanetary magnetic field is not significant.View full abstractDownload PDF (1039K) -
Isamu Nagano, Satoshi Yagitani, Hirotsugu Kojima, Hiroshi Matsumoto1996 Volume 48 Issue 3 Pages 299-307
Published: March 20, 1996
Released on J-STAGE: May 25, 2007
JOURNAL FREE ACCESSMany chorus emissions were observed in the frequency range from 200 Hz to 1 kHz when the GEOTAIL spacecraft was skimming inside the dayside magnetopause. The Wave Form Capture (WFC) onboard GEOTAIL obtained simultaneous wave forms of two electric and three magnetic components of the emissions. Spectral structures of the chorus emissions observed by the WFC are roughly classified into four types: rising tone, falling tone, hook, and structureless. In this paper, as a preliminary report, the wave normal directions for each type of the emissions except for the structureless are derived by the Means' method around the geomagnetic field line to know their propagation characteristics. In addition, Poynting directions of the chorus emissions are derived by using their five electromagnetic components. Derived propagation directions of the chorus emissions along a GEOTAIL orbit indicate that they are generated around the dayside geomagnetic equator, which is consistent with the well-known model of chorus generation through cyclotron resonance in the dayside outer magnetosphere.View full abstractDownload PDF (1668K) -
Akira Morioka, Hiroshi Oya1996 Volume 48 Issue 3 Pages 309-318
Published: March 20, 1996
Released on J-STAGE: May 25, 2007
JOURNAL FREE ACCESSQuasi pulsive depleting plasma density variations with period ranging from a few to a few tens sec with depletion up to 30 to 50% of the ambient non-depleted plasmapause density have been observed in the occasion of the plasmapause crossing by the Akebono (EXOS-D) satellite, in association with the enhancements of the local upper hybrid mode plasma waves. The phenomena are strictly related to the magnetospheric substorm phenomena with enhancements of normal kilometric radiations (AKR) which are emitted from the auroral region. These evidences are concluded to be caused by quasi-pulsive energy injections into the plasmapause region from the plasma sheet, possibly in the form of fast plasma streams, relating to substorms and magnetospheric disturbances. As for the origin of the simultaneous energy injection into the auroral and sub-auroral regions, the induced electric field by the disruption and/or the rapid change of the current sheet in the inner plasma sheet are discussed. The induced electric field should enhance the fast plasma injection from the inner magnetosphere to the plasmapause region due to the E x B drift, and also the field should be transported down to the amoral region along magnetic fields making a concentrated particle acceleration region which cause the enhancement of AKR.View full abstractDownload PDF (2138K) -
T. Abe, S. Watanabe, B. A. Whalen, A. W. Yau, E. Sagawa1996 Volume 48 Issue 3 Pages 319-325
Published: March 20, 1996
Released on J-STAGE: May 25, 2007
JOURNAL FREE ACCESSWe present a statistical analysis of thermal H+ and O+ ion flux measurements in the high-altitude (6000-9000 km) polar ionosphere from the Suprathermal ion Mass Spectrometer (SMS) on Akebono. It is shown that the normalized H+ polar wind flux (to 2000 km altitude) varies from 107 to 108 cm-2s-1 at 2000 km altitudes. Surprisingly, the O+ ion flux is found to be comparable to the H+ ion flux and much higher than classical theory prediction. The magnetic local time (MLT) distribution of the upward ion flux and its geomagnetic activity (Kp) dependence are also presented. At both magnetically quiet and active times, the integrated H+ ion flux is largest in the noon sector (09-15 MLT) and smallest in the midnight sector (21-03 MLT); the flux ratio was found to be approximately one order of magnitude. The total flux of H+ ion outflow integrated over the polar ionosphere (ILAT ≥ 75°) and over all local times was found to correlate inversely with the Kp index. The integrated H+ flux (ILAT ≥ 75°) in quiet times was 0.9∼1.5 x 1025 ions s-1 while the flux in active times was a factor of 2∼3 smaller (0.4∼0.6 x 1025 ions s-1). It also exhibited a slight positive correlation with the IMF (interplanetary magnetic field) Bz component.View full abstractDownload PDF (1561K) -
T. Obara, T. Mukai, H. Hayakawa, K. Tsuruda, A. Matsuoka, A. Nishida1996 Volume 48 Issue 3 Pages 327-335
Published: March 20, 1996
Released on J-STAGE: May 25, 2007
JOURNAL FREE ACCESSAkebono (EXOS-D) observations demonstrated that the electric field in the polar cap region is very irregular and electron precipitation spikes are prevalent when the interplanetary magnetic field (IMF) is directed northward. Comparison of the electric field and the particle precipitation shows that most electron precipitations occur in the divE < 0 regions. The variation of the electric field was predominantly seen in the dawn-to-dusk (Ey) component rather than in the noon-midnight (Ex) component, when the observations were made in the nightside polar cap region. This means thatthe particle precipitation region is basically sun-aligned in the nightside polar cap region. However, in the dayside polar cap region, the contribution of the Ex component to divE is larger, which suggests that the orientation of the elongation is not exactly sun-aligned but also has a zonal component on the dayside. The average energy of the precipitating electrons was in a range from 100 eV to 200 eV. The magnetosheath/mantle is the likely source region of the precipitating electrons in the polar cap during northward IMF conditions.View full abstractDownload PDF (1581K) -
Y. Kiyama, K. Kita, N. Iwagami, T. Ogawa1996 Volume 48 Issue 3 Pages 337-341
Published: March 20, 1996
Released on J-STAGE: May 25, 2007
JOURNAL FREE ACCESSTemporal variations of the all-sky distribution of atomic oxygen 630 nm airglow intensity were observedatMt. Haleakala in Maui Island, Hawaii, to obtain informationonthe dynamics of F region plasma in the equatorial anomaly region. All-sky intensity distribution of the hydroxyl OH(7, 2) band airglow originating from the mesopause region was simultaneously observed to seek any relationship between the dynamical variations of F region plasma and the disturbance in the lower atmosphere. The results of our preliminary analyses of the data obtained in February and November 1993 show that there is no definite correlation in the patterns of all-sky intensity distribution between atomic oxygen 630 nm and OH(7, 2) band airglows in both geomagnetically disturbed and quiet nights. The all-sky intensity pattern of 630 nm is found to be modified during a geomagnetic storm, while that of OH(7, 2) band varies independently of geomagnetic activity.View full abstractDownload PDF (986K) -
K. Mohanakhmar1996 Volume 48 Issue 3 Pages 343-352
Published: March 20, 1996
Released on J-STAGE: May 25, 2007
JOURNAL FREE ACCESSA study on the influence of solar activity and phases of equatorial quasi-biennial oscillation (QBO) on tropical rainfall over India has been made. The results of the total rainfall over the country indicate that during the period of low solar activity, excess/normal rainfall (frequent floods) are associated with the westerly phase of QBO and deficient/normal rainfall (frequent droughts) corresponded to the easterly phase. During the period of high solar activity only normal rain is observed when QBO is in its westerly phase. Multiple regression analysis has employed to estimate the summer monsoon rainfall using sunspot number and equatorial zonal wind at 15-20 hPa during January-February as independent parameters. A study on the spatial variability of monsoon rainfall in response to the solar activity and phases of QBO has also been attempted.View full abstractDownload PDF (1931K) -
Kin-aki Kawabata, Hideo Ogawa, Yoshinori Yonekura1996 Volume 48 Issue 3 Pages 353-360
Published: March 20, 1996
Released on J-STAGE: May 25, 2007
JOURNAL FREE ACCESSThe J= 61, 5-60, 6 (110.836 GHz) line of strato-mesopheric ozone has been measured employing a millimeterwave ozone sensor equipped with an SIS mixer receiver since January 1992 in a sporadic manner. The receiver noise of the SIS mixer is 34 K (SSB), and the spectrometer covers 60 MHz with a frequency resolution of 35 kHz at the present. W e can retrieve altitude profiles of O3 in the altitude range of 35-80 km from the observed spectral line. Monthly averaged diurnal variations in September 1993 and January 1994 are illustrated by step of 0.125 in logp, where p denotes the atmospheric pressure. Time relative variations of ozone concentration in the mesosphere at dawn and dusk are measured with a time resolution of 3 minutes from December 1993 through February 1994. Difference in nighttime variations of ozone concentration are briefly discussed day by day.View full abstractDownload PDF (1472K)
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