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J. Geophys. Res. 103 (A2):1981-1989, 1998.
© American Geophysical Union
Heliospheric tomography using interplanetary scintillation observations.
2. Latitude and heliocentric distance dependence of solar wind structure at 0.1-1 AU.
M. Kojima, M. Tokumaru, H. Watanabe, A. Yokobe and K. Asai
Solar-Terrestrial Environment Laboratory, Nagoya University, Toyokawa, Japan
B.V. Jackson and P. Hick
Center for Astrophysics and Space Sciences
University of California San Diego, La Jolla, California, USA
Abstract
Interplanetary scintillation is a useful means to measure the solar wind in
regions inaccessible to in situ observation, However, interplanetary scintillation
measurements involve a line-of-sight integration, which relates contributions from
all locations along the line of sight to the actual observation. We have developed
a computer assisted tomography (CAT) program to reduce the adverse effects of the
line-of-sight integration. The program uses solar rotation and solar wind motion
to provide three-dimensional perspective views of each point in space accessible
to the interplanetary scintillation observations and optimizes a three-dimensional
solar wind speed distribution to fit the observations. We analyzed IPS speeds
observed at the Solar-Terrestrial Environment Laboratory and confirmed that (1)
the solar wind during the solar minimum phase has a dominant polar high-speed
solar wind region with speeds of about 800 km s-1
and within 30 degrees of the solar equator speeds decrease to 400
km s-1 as observed by Ulysses, and (2)
high-speed winds get their final speed of 750-900
km s-1 within 0.1 AU,
and consequently, that acceleration of the solar wind is small above 0.1 AU.
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