1994 Fiscal Year Final Research Report Summary
Study of solar wind acceleration mechanisms with coordinated interplanetary scintillation observations at different frequencies.
| Project/Area Number |
04640424
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
Space and upper atmospheric physics
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| Research Institution | Nagoya University |
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Principal Investigator |
KOJIMA Masayoshi Solar-Terrestrial Environment Laboratory, Nagoya Univ., Professor., 太陽地球環境研究所, 教授 (70023687)
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| Co-Investigator(Kenkyū-buntansha) |
MORI Hirotaka Communications Research Laboratory, Chief Scientist., 通信総合研究所, 室長
MISAWA Hiroaki Solar-Terrestrial Environment Laboratory, Nagoya Univ., Research Associate., 太陽地球環境研究所, 助手 (90219618)
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| Project Period (FY) |
1992 – 1994
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| Keywords | Interplanetary Plasma / Solar Wind / Acceleration mechanism / MHD Wave / Random Velocity / Inner Scale / Ulysses |
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| Research Abstract |
1. We studied the origin of a low-speed solar wind using the solar wind speed measured by interplanetary scintillation (IPS), the soft X-ray solar corona data observed by the Yohkoh satellite, and photospheric magnetic field. We have found that the low-speed wind originated from over a sun spot region has a lower speed than that from the magnetic neutral line on the source surfase.
2. We observed the phenomena of large acceleration in high-speed solar winds at distances of 0.1-0.3 AU using the IPS method. To confirm the reliability of the observational results, we estimated possible biasing effects in the observations by computer simulation. we have found that any biasing effects cannot cause the observational phenomena of the large acceleration.
3. We studied the inner scale in micro turbulence using the IPS data observed at microfrequencies. The inner scale shows small but significant difference between a high-speed wind and a low-speed wind. This suggests that the inner scale is determined by cyclotron dumping. We also found that the behavior of the inner scale near the sun suggesting non-radial density divergence caused by solar wind acceleration.
4. We studied the random velocity which is expected to be related to the MHD waves in the solar wind. We found that the radial distance dependence is obviously different between a high-speed wind and a low-speed wind : the high-speed wind shows increase of the random velocity at 0.1 AU,while the low-speed wind shows no radial distance dependency up to 0.1 AU.
5. We made comparison of the solar wind speeds measured by the Ulysses and by the IPS.We found that if the turbulence level of density is proportional inversely to the root square of a speed, the IPS speeds agree with the Ulysses observations.
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