MAGNETIC HELICITY CHANGES OF SOLAR ACTIVE REGIONS |
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Yong-Jae Moon Submitted: 2003-04-18 11:52
In this paper, we review
recent studies on the magnetic helicity changes of solar active regions
by photospheric horizontal motions.
Recently, Chae(2001) developed a methodology to determine
the magnetic helicity change rate via photospheric horizontal motions.
We have applied this methodology to four cases:
(1) NOAA AR 8100 which has a series of homologous X-ray flares,
(2) three active regions which have four eruptive major X-ray flares,
(3) NOAA AR 9236 which has three eruptive X-class flares,
and (4) NOAA AR 8668 in which a large filament was under formation.
As a result, we have found several interesting results.
First, the rate of magnetic helicity injection strongly depends
on an active region and its evolution. Its mean rate ranges from
4 to 17 imes 1040 mbox{ Mx}^2 mbox{ h}-1.
Especially when the homologous flares occurred and
when the filament was formed, significant rates of magnetic
helicity were continuously deposited
in the corona via photospheric shear flows.
Second, there is a strong positive correlation between the magnetic
helicity accumulated
during the flaring time interval of the homologous flares in AR 8100
and the GOES X-ray flux integrated over the flaring time.
This indicates that the occurrence of a series of homologous
flares is physically related to the accumulation of magnetic
helicity in the corona by photospheric shearing motions. Third,
impulsive helicity variations took place near the flaring times of
some strong flares. These impulsive variations whose time
scales are less than one hour are
attributed to localized velocity kernels around the polarity inversion line.
Fourth, considering the filament eruption associated with an X1.8 flare
started about 10 minutes before the impulsive variation of the helicity change rate,
we suggest that the impulsive helicity variation
is not a cause of the eruptive solar flare but its result.
Finally, we discuss the physical implications
on these results and our future plans.
Authors: Y.-J. Moon, Jongchul Chae, and Y. D. Park
Projects: Soho-MDI
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Publication Status: JKAS, in press
Last Modified: 2003-04-18 11:52
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