Determination of Magnetic Helicity of Solar Active Regions Using the Linear
Force-free Field Model.
Lim Eun kyung , Chae Jongchul
Magnetic helicity is a useful quantity in characterizing the magnetic
system of solar active regions. We aim to measure the helicity of the
coronal magnetic field of an active region based on the linear force-free
field assumption. With a value of the force-free , the coronal field is
constructed from the extrapolation of SOHO/MDI magnetograms, and the
constructed field lines are compared with the coronal loops in the EUV
images taken by SOHO/EIT. The force-free that best fits the loops is used
to calculate the helicity of the active region. We have applied this method
to AR 10696 during its first rotation so that obtained the range of value
and the tempposter variation of magnetic helicity. We have compared our
results with the accumulated amount of the helicity transferred to the
corona via the photosphere which is determined independently. We find that
the two different methods yielded helicity values that are consistent
within the difference of about 30~40%. The major difference is that the
coronal helicity decreased one day while the injected helicity steadily
increased all the time. The decrease was due to a couple of CMEs that
occurred during the same day.
Correspondence
Eun-Kyung Lim (uklim@astro.snu.ac.kr), Seoul National University
presentation
poster