Grant-in-Aid for General Scientific Research (C)
|Allocation Type||Single-year Grants|
Space and upper atmospheric physics
|Research Institution||National Institute of Polar Research|
KADOKURA Akira(1994-1995) National Institute of Polar Research, Research Associate, 資料系, 助手 (70185883)
山岸 久雄(1993) 国立極地研究所, 研究系, 助教授 (20132714)
YUKIMATU Akira National Institute of Polar Research, Research Associate, 研究系, 助手 (70260007)
MIYAOKA Hiroshi National Institute of Polar Research, Associate Professor, 情報科学センター, 助教授 (10150046)
YAMAGISHI Hisao National Institute of Polar Research, Associate Professor, 研究系, 助教授 (20132714)
KIKUCHI Masayuki National Institute of Polar Research, Research Associate, 研究系, 助手 (20270423)
菊地 崇 通信総合研究所, 宇宙科学部, 主任研究官
菊池 崇 通信総合研究所関東支所, 平磯太陽地球環境研究センター, センター長
門倉 昭 国立極地研究所, 研究系, 助手 (70185883)
|Project Period (FY)
1993 – 1995
Completed(Fiscal Year 1995)
|Budget Amount *help
¥2,000,000 (Direct Cost : ¥2,000,000)
Fiscal Year 1995 : ¥500,000 (Direct Cost : ¥500,000)
Fiscal Year 1994 : ¥500,000 (Direct Cost : ¥500,000)
Fiscal Year 1993 : ¥1,000,000 (Direct Cost : ¥1,000,000)
|Keywords||Aurora / Imaging Riometer / Geomagnetic Conjugate Point / Ionospheric Radio Absorption / Symmetricity between the both hemispheres / CNA / Iceland / Magnetospheric Magnetic Field Model / 磁気圈磁場モデル|
In the final year of this grant, we have completed compilation of Syowa-Iceland conjugate imaging riometer data for the period from February 1993 to January 1995. Summary plots of the riometer outputs of north-south and east-west line of beams are also prepared for this period.
In the last year, we have determined the geomagnetic conjugate point experimentally from the relative location of auroral absorption arcs observed by the imaging riometers in the both hemispheres. We have found that the conjugate point of Syowa Station mapped on Iceland located at lower latitude of Tjornes in July, but at higher latitude in January. This qualitatively agrees with the results of geomagnetic conjugate point calculations based on magnetospheric models.
Physrcal interpretation of this seasonal change was considered in this year.
(1) Latitudinal shift of the conjugate point is controlled by tilt angle of the geomagnetic dipole axis to the ecliptic plane. Solar wind plasma gives more pressure to the magn
etic field lines in the dayside summer hemisphere than in the dayside winter hemisphere. This causes foot points of the field lines in the summer hemisphere to move toward higher latitude in the dayside and lower latitude in the nightside. In the winter hemisphere, where relatively lower solar wind pressure gives the field lines to progress toward magnetopause, foot points of the field lines tend to move toward lower latitude in the dayside and higher latitude in the nightside.
(2) Longitudinal shift of the conjugate point is related to the fact that a field line anchorred in higher latitude tends to be stretched more deep into the magnetotail. Consider a field line passing through a certain point in the morningside magnetotail and compare the local time of the foot points of this field line in the both hemispheres. For dayside summer hemisphere, where the foot point is located at higher latitude than in the winter hemisphere, the local time of the foot point is located nearer to the noon as compared to that of the opposite hemisphere, because the portion of the field line in the summer hemisphere is stretched more longer than that in the winter hemisphere. This feature causes the conjugate point in the summer hemisphere to move toward east in prenoon hours and west in the postnoon hours.
Combining the features mentioned in (1) and (2), a conjugate point of antarctic region mapped in the northern hemisphere will show daily motion along elliptic trace in counter clockwise direction. Phase of this rotational motion is dependent upon season in a way that the conjugate point is located at the highest latitude at midnoon in summer (July) and midnight in winter (January). This feature is universal for all polar region. Less