R. -S. Kim, N. Gopalswamy, Y. -J. Moon, K. -S. Cho, S. Yashiro
To measure the magnetic field strength in the solar corona, we examined 10
fast (> 1000 km/s) limb CMEs which show clear shock structures in SOHO/LASCO
images. By applying piston-shock relationship to the observed CME's standoff
distance and electron density compression ratio, we estimated the Mach number,
Alfven speed, and magnetic field strength in the height range 3 to 15 solar
radii (Rs). Main results from this study are: (1) the standoff distance
observed in solar corona is consistent with those from a magnetohydrodynamic
(MHD) model and near-Earth observations; (2) the Mach number as a shock
strength is in the range 1.49 to 3.43 from the standoff distance ratio, but
when we use the density compression ratio, the Mach number is in the range 1.47
to 1.90, implying that the measured density compression ratio is likely to be
underestimated due to observational limits; (3) the Alfven speed ranges from
259 to 982 km/s and the magnetic field strength is in the range 6 to 105 mG
when the standoff distance is used; (4) if we multiply the density compression
ratio by a factor of 2, the Alfven speeds and the magnetic field strengths are
consistent in both methods; (5) the magnetic field strengths derived from the
shock parameters are similar to those of empirical models and previous
estimates.
View original:
http://arxiv.org/abs/1112.0288
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