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Volume 47, Issue 10
Displaying 1-9 of 9 articles from this issue
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Akira Iwata, Yoshihito Tanaka, Masanori Nishino, Kiyohumi Yumoto1995 Volume 47 Issue 10 Pages 943-952
Published: October 20, 1995
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSEnergetic electrons observed by the NOAA-6 satellite are compared with the LF whistler-mode signals from a Decca navigation station (Biei, L = 1.54, fc = 85.725 kHz), measured in the magnetic conjugate area of the transmitter around Birdsville, Australia. These electron data are also compared with VLF/ELF emissions observed at Moshiri (L = 1.57) and Kagoshima (1.2). The VLF/ELF emissions occurred almost simultaneously with enhanced auroral electrojet (AE) activities. The intensity increase of the LF signals were the largest on one day after the maximum depression phase of Dst, and the intensity peaks appeared with time delays behind enhanced AE activities. These indicate that energetic electrons associated with enhanced AE activities, rapidly penetrate into the plasmapause latitude, where they genarate VLF/ELF emissions by cyclotron resonance interactions. Futhermore, energetic electrons of 50-100 keV invade with time delays deep into the low-L shell region below ∼2, where the wave growth of the LF signals may be caused by additional injection of these electrons, superimposed on energetic electrons more than 30 keV penetrating at the maximum Dst phase. So, the penetration of energetic electrons deep into the magnetosphere may be deduced from ground-based measurements of resonant waves at low latitudes.View full abstractDownload PDF (1811K) -
Heikki Nevanlinna1995 Volume 47 Issue 10 Pages 953-960
Published: October 20, 1995
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSSystematic naked eye sightings of northern lights started in Finland in 1748. Such observations were carried out for about 100 years at two places in Southern Finland. All observations were compiled and published by Hällström (1847). Auroral occurrence frequencies in this compilation obey well the semiannual variation and the 11-year sunspot cycle when compared with other coeval auroral and magnetic data available in Europe. In the middle of the 100-year auroral series there was an anomalous period of very low auroral occurrence, known as Dalton's solar activity minimum, lasting about three decades from 1795 to 1825. As a signature of Dalton's minimum, auroras were totally absent from the sky in Southern Finland for the 10 years 1806-1815.View full abstractDownload PDF (1755K) -
T. Imamura, K. Kita, N. Iwagami, T. Ogawa1995 Volume 47 Issue 10 Pages 961-972
Published: October 20, 1995
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSWe investigated the fine structures of lower thermospheric atomic oxygen and electron density profiles obtained by a rocket experiment, assuming that these structures are due to a quasi-monochromatic internal gravity wave. The dissipation process of a gravity wave was inferred from the atomic oxygen profile. The height variation of the horizontal wind amplitude is similar to that of the intrinsic horizontal phase speed below ∼105 km, implying an evidence of saturation effects. At higher altitudes, dissipation due to molecular diffusion was suggested. The propagation direction of the wave was determined from both atomic oxygen and electron profiles based on the fact that the response of ionic species to gravity waves is different from that of neutral species depending on the propagation direction. The propagation direction inferred is interpreted as a consequence of selective transmission of gravity waves in lower atmosphere.View full abstractDownload PDF (2301K) -
K. Asamura, T. Iyemori1995 Volume 47 Issue 10 Pages 973-987
Published: October 20, 1995
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSThe ionospheric neutral wind is induced by the ion drag forcing under the sufficiently continuous southward IMF conditions in the polar region. If the IMF turns northward sharply after prolonged southward interval, the neutral wind gives its own momentum to the charged particles and makes the ionospheric currents. This phenomenon is one of the forms of “flywheel” effect. To ascertain the existence of the flywheel effect and to obtain its global pattern in the polar region we analyzed the ionospheric equivalent current system derived from ground-based geomagnetic observation by superposed epoch method. The results show (1) appearance of dawnward and antisunward currents after IMF northward turning, (2) its attenuation with a time constant of several hours, (3) seasonal dependence in the attenuation time constant, (4) small day-night difference in the current intensity after the turning. The antisunward current is stronger for the case with prolonged southward IMF interval before the northward turning than that for short and weak southward IMF case. These results are consistent with the theoretical expectations of the flywheel effect, though there are some difference with the prediction by computer simulations in the global current pattern such as the dawnward rotation of the current vector.View full abstractDownload PDF (2575K) -
Motoaki Yasui, Motowo Fujiwara, Hideharu Akiyoshi, Seiji Ikawa, Hidefu ...1995 Volume 47 Issue 10 Pages 989-998
Published: October 20, 1995
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSStratospheric aerosols originating from the June 1991 explosive eruptions of Mt. Pinatubo has been observed at Fukuoka with a Nd:YAG lidar. Sudden increase of the aerosols in the vicinity just above the tropopause in July 1991 was followed by the appearance of extraordinary strong scattering layer around 21-22 km height. The volcanic aerosols stratified in two distinct layers merged into a broad layer when the background wind field changed from the easterlies to the westerlies and the bulk of the aerosols arrived. After having taken its maximum in the first winter the aerosol burden decreased monotonously. Superposed on the decrease we can read the seasonal variations associated with the seasonal variation in the wind field and the tropopause height also after the second year. Height of the center of gravity of the aerosols relative to the height of tropopause have been approaching gradually to a constant value.View full abstractDownload PDF (1826K) -
Yasuo Sonoi, Yasuyuki Maekawa, Zen-Ichiro Kawasaki, Fumio Yoshino, Sho ...1995 Volume 47 Issue 10 Pages 999-1010
Published: October 20, 1995
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSThe authors investigate the characteristics of thunderclouds associated with lightning phenomena in the winter season using the dual polarization Doppler radar of the Ministry of Construction known as the DND (Dobokuken-Nijuhenpa-Doppler) radar. This paper deals with the discrimination between different types of precipitation particles and presents the relationship between the movement of the particles and lightning processes. Our results suggest that the dual polarization observational mode, detecting both the horizontal radar reflectivity factor (ZH) and the differential reflectivity factor (ZDR), may discriminate between precipitation particles such as graupel or ice crystals, and that the observed radar echoes indicate a close relationship between the contact of these precipitation particles and the lightning process. Also, simultaneous field-mill observations suggest that graupel has negative charge while ice crystals have positive charge in thunderclouds. This electrical phenomenon is well described in terms of recent thunderstorm electrification theories at temperatures below -10°C.View full abstractDownload PDF (2371K) -
Hidetoshi Shibuya, John Cassidy, Ian E. M. Smith, Tetsumaru Itaya1995 Volume 47 Issue 10 Pages 1011-1022
Published: October 20, 1995
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSA paleosecular variation (PSV) study was carried out on monogenic basalt volcanoes of the northern part of North Island, New Zealand. A new method of calculating angular standard deviation (ASD) by fitting a combination of two Fisher distributions to the cumulative histogram of VGP data is presented, which avoids the necessity of applying an arbitrary cut-off angle to exclude intermediate magnetic directions. The resultant ASD of 11.5° for northern New Zealand is smaller than that predicted by previous PSV models. Using this new method, recalculation of published data from elsewhere spanning the last 10Ma suggests that the ASD commonly has been over-estimated and that the global distribution of ASD exhibits a significant longitudinal variation. This relatively long-term non-axisymmetric distribution of ASD implies that the core dynamo process may be strongly influenced by the thermal and/or mechanical regime of the solid mantle.View full abstractDownload PDF (2408K) -
M. Itonaga1995 Volume 47 Issue 10 Pages 1023-1027
Published: October 20, 1995
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSAt low latitudes, the phase of H component of the ground magnetic perturbation can be expected to be independent of the latitude for low-frequency geomagnetic pulsations. Because of such a spatial phase structure of the H component, it is found that the D component has a 180° out-of-phase relation between the northern and southern hemispheres and its amplitude increases monotonously from the magnetic equator to higher latitudes. It is also shown that the sense of rotation of the magnetic perturbation vector in the H-D plane is clockwise and counterclockwise for the eastward and westward propagations, respectively, in the northern hemisphere and vice versa in the southern hemisphere. On the other hand, since the spatial phase structure of the H component far away from the magnetic equator becomes more complicated as the latitude increases, the correlation between signal propagation sense and horizontal polarization may deteriorate at high latitues. For the amplitudes of H and D components due to the compressional component of the magnetic field incident upon the ionosphere their upper bounds are also given.View full abstractDownload PDF (1066K) -
F. H. Hibberd1995 Volume 47 Issue 10 Pages 1029-1031
Published: October 20, 1995
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSThe amplitude of the annual variation in the horizontal component of Sq is larger in the southern hemisphere than the northern hemisphere. This asymmetry may be represented as the superposition of a world-wide annual variation with its maximum at or near perihelion and summer-winter annual variations of equal amplitudes in the two hemispheres and maxima at the local summer solstice. The amplitude of the world-wide annual variation, as a fraction of the yearly mean value of Sq, is about 0.07 ± 0.02. The variation in ionospheric conductivity associated with the earth's orbital eccentricity is inadequate alone to account for this annual variation in Sq. If joule heating by the Sq currents is appreciable, its annual and semi-annual variations could account for the similar variations in the temperature of the thermosphere.View full abstractDownload PDF (655K)
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