Issue |
A&A
Volume 400, Number 1, March II 2003
|
|
---|---|---|
Page(s) | 347 - 353 | |
Section | The Sun | |
DOI | https://doi.org/10.1051/0004-6361:20021844 | |
Published online | 24 February 2003 |
Plasma properties above coronal active regions inferred from SOHO/UVCS and radio spectrograph observations
1
Istituto Nazionale di Astrofisica (INAF), Osservatorio Astronomico di Torino, Strada Osservatorio 20, Pino Torinese 10025, Italy
2
Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS 50, Cambridge, MA 02138, USA
Corresponding author: S. Mancuso, mancuso@to.astro.it
Received:
28
October
2002
Accepted:
13
December
2002
Information on coronal plasma was inferred from the
joint analysis of type ii radio bursts and SOHO UltraViolet
Coronagraph Spectrometer (UVCS) observations. The data sample
comprises 37 metric type ii radio bursts observed by
ground-based radio spectrographs in 1999, during the rising phase
of the solar cycle. The coronal electron densities ne were
estimated with the diagnostic provided by UVCS observations of the
doublet line intensities. Upper limits to the coronal
Alfvén speed above active regions were inferred from the derived
shock speeds by requiring that the disturbances propagate at least
faster than the local characteristic speed. Information on the
magnetic field strength B and plasma β in the middle
corona were finally extracted from the coronal Alfvén speed upper
limits. A major improvement with respect to previous studies that
used type ii radio bursts to derive plasma properties, is
that density profiles of the pre-shock plasma obtained a few
hours before the passage of the shock were used instead of general electron
density models taken from literature. Our main result is expressed
by the inequality
G, that
is valid in the range
solar radii, and is
consistent with previous estimates of the magnetic field above
coronal active regions.
Key words: Sun: corona / Sun: UV radiation / Sun: magnetic fields / Sun: radio radiation / Shock waves
© ESO, 2003
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