| Project/Area Number |
17540424
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Space and upper atmospheric physics
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| Research Institution | Tohoku Institute of Technology |
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Principal Investigator |
NAKAGAWA Tomoko Tohoku Institute of Technology, 工学部, Associate Professor (40222161)
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| Project Period (FY) |
2005 – 2007
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| Project Status |
Completed (Fiscal Year 2007)
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| Budget Amount *help |
¥2,050,000 (Direct Cost: ¥1,900,000、Indirect Cost: ¥150,000)
Fiscal Year 2007: ¥650,000 (Direct Cost: ¥500,000、Indirect Cost: ¥150,000)
Fiscal Year 2006: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 2005: ¥900,000 (Direct Cost: ¥900,000)
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| Keywords | solar wind acceleration / CME / space plasma / SOHO / LASCO / MHD wave / type III bursts / magnetic rope / multi-spacecraft observations / CME(コロナルマスイジェクション / force-free field / フラックスロープ / 多点衛星観測 / トーラス型磁気ロープ / のぞみ / タイプIIIパースト / IMF / 強度変動 / 密度ゆらぎ / 20太陽半径 |
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| Research Abstract |
(1) By using the linear relationship between the initial speed and the initial acceleration of the limb CMEs, the solar wind speed in the vicinity of the Sun is estimated on the assumption that a dragging force is acting depending on the speed difference between the CMEs and the ambient plasma. The solar wind speed within 20 solar radii estimated from the low-latitude CMEs ranged from 100 to 700 km s^<-1>, while the solar wind speed measured at 1 AU ranged from 300 to 700 km s^<-1>. It suggests that the low-latitude solar wind almost completes accelerating within 20 solar radii, but occasionally additional acceleration is present beyond 20 solar radii.
(2) Magnetohydrodynamic (MHD) waves are thought to play an important role in heating and acceleration of the solar wind. An attempt was made to detect MHD waves in the decametric type-3 solar radio bursts in the frequency range from 15 to 40 MHz. There found 1-3 peaks at around 18, 23, or 31 MHz in the spectra, corresponding to the distance of about 1.3 to 1.7 solar radii from the Sun. It suggests that the effective energy conversion from electron-beam driven Langmuir waves to electromagnetic waves occurs under the enhanced plasma density fluctuations of the compressive MHD waves which are responsible to solar wind acceleration.
(3) A torus-type flux rope model applied to an interplanetary magnetic cloud was tested by the simultaneous magnetic field observations by ACE and NOZOMI spacecraft. On the basis of a single observation by ACE, the magnetic cloud was once fitted to a torus-shaped flux rope model through which the spacecraft passed at the southern tip, however, this study revealed that the spacecraft passed through the southern tip, suggesting that the magnetic rope originating from the northern hemisphere of the Sun crosses the equatorial plane.
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