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Volume 46, Issue 10
Displaying 1-8 of 8 articles from this issue
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Masako Sasaki, Shu Takeshita, Masahisa Sugiura, Toshibumi Sakata1994 Volume 46 Issue 10 Pages 827-834
Published: October 20, 1994
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSThe global solar ultraviolet-B (UV-B: 290-320 nm) irradiance has been measured by a newly designed band-spectral solar UV-B radiometer at Tokai University, Hiratsuka (35°N, 139°E), Japan from October 1990 to April 1994. The global solar total (Total: 300-3300 nm) irradiance has also been measured by a pyranometer. When the seasonal variation is removed by taking 12-month moving averages, an increase at an average rate of 3.4% per year is found in the monthly averages of daily integrated global solar UV-B irradiance. In contrast, the monthly averages of daily integrated global solar Total irradiance remained nearly constant throughout the same period. The existence of a linear trend over the above time period is confirmed by a statistical method different from the analysis of the moving averages, using the global solar UV-B irradiance normalized by dividing it by the global solar Total irradiance. Corresponding to the increase in the global solar UV-B irradiance, a decrease is found in the total ozone amount measured at Tateno (35°N, 140°E), offering supportive evidence for a direct link between these two parameters.View full abstractDownload PDF (19025K) -
Munetoshi Tokumaru, Tetsuro Kondo, Hirotaka Mori, Takashi Tanaka1994 Volume 46 Issue 10 Pages 835-849
Published: October 20, 1994
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSSingle-station observations of interplanetary scintillation (IPS) at two frequencies; 2 GHz and 8 GHz, have been made simultaneously between 1990 and 1992 at the Kashima Space Research Center. The solar wind velocity near the sun is derived from these IPS observations by means of a co-spectrum technique. Derived velocities clearly reveal that solar wind acceleration occurs at radial distances between 12 and 80 Rs (solar radii), although the velocity structure on the solar surface occasionally influences the radial variation of our IPS data. A close association between high-speed winds and the coronal hole is demonstrated by comparing our IPS data with He (1083 nm) observations. Our velocity estimates are then compared with speeds obtained from three-station IPS measurements at 327 MHz. Consequently, a good agreement is found with IPS data taken in 1992, whereas the correlation is lost with IPS data from 1991 owing to the systematic bias between two measurements. It is shown that our velocity estimates are slightly higher than three-station estimates at large radial distances, and that this relation is reversed within 30 Rs. While the cause of this radial dependence is not fully understood, some possible effects are discussed here.View full abstractDownload PDF (38596K) -
M. Ejiri, A. Kadokura, T. Oguti1994 Volume 46 Issue 10 Pages 851-860
Published: October 20, 1994
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSThe visible (Oxygen green line: 557.7 nm) TV camera aboard EXOS-D (Akebono) takes successive auroral images every 8 sec, which are characterized as a snapshot image of a wide area with high spatial and temporal resolutions. The followings are some preliminary results, when the satellite was located at altitudes of 3000 to 4700 km in the southern hemisphere. (1) At the magnetospheric disturbances, the faint enhanced aurora (MLT width less than about 0.2 hours ≈3°) along the meridian at the pre-midnight was formed, extending from 74° CGL down to 65° CGL. The brightening of the spot was first activated at the higher latitude with subsequent propagation/elongation to the lower latitude. (2) During the storm recovery phase the brightening was confined to a small region (MLT width being less than 0.2 hours or about 330 km across in the ionosphere) of discrete aurora in the high latitude side of the midnight auroral oval. Newly intensified auroral arcs along the pre-existing faint discrete aurora were successively coming out to the westwards. (3) The discrete auroral arc showed a clockwise rotation viewed in the direction of the geomagnetic field. (4) Interestingly, a 557.7 nm airglow layer was observed whenever the field of view covered the earth's limb.View full abstractDownload PDF (32228K) -
I. Oznovich, D. J. McEwen1994 Volume 46 Issue 10 Pages 861-871
Published: October 20, 1994
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSDuring the first 12 1/2 hours of February 17, 1993, 21 apparently-isolated events of discrete polar arcs were recorded in broad-band visual light by an all-sky camera and in the blue, green, and red lines by a meridian scanning photometer at Eureka, an observatory near the north magnetic pole (89° magnetic latitude). The polar arcs were located almost exclusively in the dusk sector. Most of the arcs (>60%) were faint (≤1 kR in the blue, green, or red lines). The remainder were bright arcs (1-17 kR in the green) associated with energy fluxes of 1-7 erg cm-2s-1 and characteristic energies of ∼0.6 keV. The average lifetime of an individual polar arc was 8 minutes. One of the 21 identified events of polar arcs was associated with diffuse emissions duskward of the arc. The faint (0.5 kR in the green) diffuse emissions extended from the dusk horizon of the camera up to the arc. They were associated with very soft (E0 < 0.4 keV) and low flux (0.2 erg cm-2s-1) particle precipitation. These emissions were probably the optical manifestation of particle entry phenomena reported in the past, namely the location of transpolar arcs at the poleward edge of continuous soft particle precipitation. The lifetime of the diffuse emission (40 min) was much longer than the lifetime of the polar arc (6 min) and it did not follow the duskward motion of the arc. We show a time sequence of a new phenomenon regarding sun-aligned arcs-short lived, antisunward propagating intensifications in the form of bright spots spread over a very small spatial scale along the arc.View full abstractDownload PDF (38895K) -
G. G. Bowman, S. Fukao, M. Yamamoto, K. Igarashi1994 Volume 46 Issue 10 Pages 873-889
Published: October 20, 1994
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSRecordings by the MU-radar of two ionospheric events involving F2-layer field-aligned irregularities (FAIs) on one particular night in a sunspot-maximum period (July 24/25, 1991) have been examined and compared with ionospheric events deduced from the analyses of ionograms from the adjacent ionosonde stations of Akita and Kokubunji. Ionograms from three other Japanese stations have also been analysed. The analyses detected two medium-scale travelling ionospheric disturbances (MS-TIDs) which pass through the MU-radar observing region at times close to those of the FAI recordings. The MS-TIDs seem to be propagating at both F2-layer and Es layer levels. F2-layer macroscale changes and Es-layer enhancement (particularly the Es enhancements) have been used to track the disturbances over significant distances from Wakkanai in the north to Yamagawa in the south, and even to the island of Okinawa (located some 2, 500 km from Wakkanai). Spread-F is recorded during the passage of these MS-TIDs, but only at some stations. Quite apart from the apparent association of these MS-TIDs with the FAI recordings, these results would seem to reinforce other results which indicate an association between macroscale F2-layer height changes and enhanced sporadic-E occurrence.View full abstractDownload PDF (51634K) -
Mioara Alexandrescu, Chau Ha Duyen, Jean-Louis Le Mouel1994 Volume 46 Issue 10 Pages 891-901
Published: October 20, 1994
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSThis study presents some characteristics of geomagnetic models computed from magnetic observatory data. We first analyse the covariance matrix of the Gauss coefficients for different data distributions and different truncation degrees of the spherical harmonic expansion. We then compute the ratio R of the mean square value of the diagonal terms of this covariance matrix to the mean square value of its off-diagonal terms. Finally, we estimate the accuracy of two main-field models, computed using annual mean values from 132 magnetic observatories and two weights series. The effect of the uneven distribution of observatories on global modelling of the geomagnetic field and its secular-variation is underlined. The accuracy of such models is good enough in the areas where the density of observatories is high enough (Europe, North America, East Asia), but it decreases dramatically in poorly covered areas.View full abstractDownload PDF (33797K) -
T. Yamagami, M. Namiki, S. Ohta, N. Yajima, H. Suzuki, Y. Hirasima, H. ...1994 Volume 46 Issue 10 Pages 903-908
Published: October 20, 1994
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSA Polar Patrol Balloon observation of cosmic ray protons (E ≥ 100 MeV) was carried out in Antarctica, also energetic X-ray (E = 30-120 keV) observations of auroral, solar and/or cosmic origins as well. The Polar Patrol Balloon No. 6 (PPB≠6) was launched from Syowa Station on January 5, 1993 and drifted westward by 1.5 circumpolar rounds over Antarctica, covering 6-13 g/cm2 atmospheric depth and 63°S-70°S geographic latitude. A total of 584 hours of observations was obtained. During the period, data telemetry and balloon tracking were performed by a multi-ID ARGOS system, through which the all data were acquired every 30 seconds. A preliminary report of fluxes and spatial distributions of cosmic ray protons and auroral X-rays is presented. Some features of the results are summarized as follows. 1) Proton fluxes measured in the polar cusp region still reveal a progressive increase at higher latitudes above the cosmic-ray latitude knee. 2) The differential energy spectrum of cosmic ray protons measured near the solar minimum is consistent with observations in 1967 and 1977. 3) Distinct enhancements of auroral X-rays were often observed, particularly dominant in the magnetic local dayside time.View full abstractDownload PDF (16927K) -
1994 Volume 46 Issue 10 Pages 909
Published: 1994
Released on J-STAGE: August 11, 2011
JOURNAL FREE ACCESSDownload PDF (60K)
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