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Evolution of the solar wind acceleration region during 1990-1994The single-station measurements of interplanetary scintillation (IPS) at 2 and 8 GHz have been made at the Kashima Space Research Center of the Communications Research Laboratory in the period from 1990 to 1994. These IPS data are used to study the radial distribution of solar wind velocity and density fluctuations near the sun (i.e. 10-70 Rs), and the long-term variation in these properties. The IPS co-spectrum technique is applied here to estimate the solar wind velocity. Derived velocities show that the solar wind gains a speed significantly in the radial range from 10 to 30 Rs (solar radii). which is much farther than the source surface of the thermally driven solar wind model. From the scintillation index analysis. it is found that the radial fall of density fluctuations is well described by the power-law function. A series of IPS observations reveals that a pronounced change in velocity and turbulence level for this radial range occurs at the polar region of the sun during 1990-1994. That is, the high speed wind and the reduced turbulence region develop there as the solar activity declines. On the other hand, little long-term variation is observed for the solar wind acceleration region at a low latitude. From the comparison with He 1O83 nm observations. it is demonstrated that the change of the solar wind structure is closely linked with the evolution of the coronal hole on the solar surface.
Document ID
19960021355
Acquisition Source
Jet Propulsion Laboratory
Document Type
Conference Paper
Authors
Tokumaru, M.
(Communications Research Lab. Hokkaido, Japan)
Kondo, T.
(Communications Research Lab. Kashima, Japan)
Takaba, H.
(Communications Research Lab. Kashima, Japan)
Mori, H.
(Communications Research Lab. Koganei, Japan)
Tanaka, T.
(Communications Research Lab. Koganei, Japan)
Date Acquired
August 17, 2013
Publication Date
June 30, 1995
Subject Category
Solar Physics
Accession Number
96N24751
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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