|
|
J. Geophys. Res. 103 (A2):1991-2001, 1998.
© American Geophysical Union
Heliospheric tomography using interplanetary scintillation observations.
3. Correlation between speed and electron density fluctuations in the solar wind.
K. Asai, M. Kojima, M. Tokumaru and A. Yokobe
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
P.K. Manoharan
Radio Astronomy Centre, Tata Institute of Fundamental Research, Udhagamandalam, India.
Abstract
We have examined the relationship between solar wind speed and electron density
fluctuations on scale sizes around 100 km in the heliocentric distance range of
0.3 to 0.8 AU using interplanetary scintillation (IPS) data obtained at the
Solar-Terrestrial Environment Laboratory. The solar wind properties derived
from the IPS data are biased by line of sight integration through a
three-dimensional structured solar wind. Therefore we have applied a
computer-assisted tomography (CAT) method to deconvolve the line of sight
integration and reconstruct the solar wind structure. The analysis was made for
the solar wind speed V and electron density fluctuations
dNe in the
solar activity minimum phase when high-speed regions are separated from an
equatorial low-speed region by a sharp velocity gradient. From results of the
CAT analysis we derived the best fit power law relation of
dNe
~ V-g
with g = 0.5 ± 0.15,
indicating that fractional density fluctuations
dNe/Ne in the high-speed wind
are larger than those in the low-speed wind. Combining this relation with results
of previous workers [Coles et al., 1995; Manoharan, 1993; Celnikier
et al., 1987; Jackson et al., 1998], we suggest that the fractional
density fluctuation level of the high-speed wind evolves with heliocentric distance.
|
|