| Project/Area Number |
07454115
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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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 | NAGOYA UNIVERSITY |
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Principal Investigator |
KOJIMA Masayoshi NAGOYA UNIVERSITY,Solar-Terrestrial Environment Laboratory, Professor, 太陽地球環境研究所, 教授 (70023687)
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| Co-Investigator(Kenkyū-buntansha) |
MISAWA Hiroaki NAGOYA UNIVERSITY,Solar-Terrestrial Environment Laboratory, Research Associate, 太陽地球環境研究所, 助手 (90219618)
SAKURAI Takayuki NAGOYA UNIVERSITY,Solar-Terrestrial Environment Laboratory, Research Associate, 太陽地球環境研究所, 助手 (52564744)
ASAI Kikuo NAGOYA UNIVERSITY,National Institute of Multimedia Education, Research Associate, メディア教育開発センター, 助手 (90290874)
TOKUMARU Munetoshi NAGOYA UNIVERSITY,Solar-Terrestrial Environment Labolatory, Associate Professor, 太陽地球環境研究所, 助教授 (60273207)
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| Project Period (FY) |
1995 – 1997
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| Keywords | solar wind / plasma / interplanetary scintillation / tomography |
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| Research Abstract |
Spacecraft observations of the solar wind have been confined to regions near the ecliptic plane except only one spacecraft of Ulysses, and there has been no direct measurement at solar distances inside 70 Rs where the solar wind is significantly accelerated. An interplanetary scintillation (IPS) method is a unique and useful means to measure global structure of the solar wind in regions near the Sun and at high latitudes where in situ measurements are difficult. However the IPS measurements are biased by a line-of-sight integration through a three-dimensional structured solar wind. So we have developed a method which uses a computer assisted tomography (CAT) technique to obtain unbiased longitudinal and latitudinal distributions of a speed and electron density fluctuations.
The CAT analyzes have retrieved not only unbiased solar wind parameters but also high spacial resolution ;
1. Fractional Electron Density Fluctuations
We found that the fractional electron density fluctuation level DELTAN/N in the high-speed wind grows with a heliocentric distance and becomes larger than that in the low-speed wind at distances beyond 0.3 AU ;
2. Latitudinal Structure
The latitudinal solar wind speed structure in the solar activity minimum phase has a bimodal structure which consists of low-speed and high-speed regions separated with a sharp velocity gradient ;
3. Radial distance dependence of velocity
Comparing two velocity distribution maps made at 0.1-0.3 AUand 0.3-IAU,we found that the high-speed wind is accelerated to its final speed within 0.1 AU and that the high-speed Wind increases its velocity slightly as approaching the sun, that is, in average from 743-804 km/s at 0.3-1 AU to 791-896 km/s at 0.1-0.3 AU.
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