1,236 research outputs found
Bootstrapping the Coronal Magnetic Field with STEREO: I. Unipolar Potential Field Modeling
We investigate the recently quantified misalignment of between the 3-D geometry of stereoscopically triangulated
coronal loops observed with STEREO/EUVI (in four active regions) and
theoretical (potential or nonlinear force-free) magnetic field models
extrapolated from photospheric magnetograms. We develop an efficient method of
bootstrapping the coronal magnetic field by forward-fitting a parameterized
potential field model to the STEREO-observed loops. The potential field model
consists of a number of unipolar magnetic charges that are parameterized by
decomposing a photospheric magnetogram from MDI. The forward-fitting method
yields a best-fit magnetic field model with a reduced misalignment of
. We evaluate also stereoscopic
measurement errors and find a contribution of , which constrains the residual misalignment to
, which is likely
due to the nonpotentiality of the active regions. The residual misalignment
angle of the potential field due to nonpotentiality is found to
correlate with the soft X-ray flux of the active region, which implies a
relationship between electric currents and plasma heating.Comment: 12 figures, manuscript submitted to ApJ, 2010 Apr 2
Coronal Loop Oscillations Observed with AIA - Kink-Mode with Cross-Sectional and Density Oscillations
A detailed analysis of a coronal loop oscillation event is presented, using
data from the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics
Observatory (SDO) for the first time. The loop oscillation event occurred on
2010 Oct 16, 19:05-19:35 UT, was triggered by an M2.9 GOES-class flare, located
inside a highly inclined cone of a narrow-angle CME. This oscillation event had
a number of unusual features: (i) Excitation of kink-mode oscillations in
vertical polarization (in the loop plane); (ii) Coupled cross-sectional and
density oscillations with identical periods; (iii) no detectable kink amplitude
damping over the observed duration of four kink-mode periods ( min);
(iv) multi-loop oscillations with slightly () different periods;
and (v) a relatively cool loop temperature of MK. We employ a
novel method of deriving the electron density ratio external and internal to
the oscillating loop from the ratio of Alfv\'enic speeds deduced from the flare
trigger delay and the kink-mode period, i.e.,
. The coupling of the kink mode and
cross-sectional oscillations can be explained as a consequence of the loop
length variation in the vertical polarization mode. We determine the exact
footpoint locations and loop length with stereoscopic triangulation using
STEREO/EUVI-A data. We model the magnetic field in the oscillating loop using
HMI/SDO magnetogram data and a potential field model and find agreement with
the seismological value of the magnetic field, G, within a
factor of two.Comment: ApJ (in press, accepted May 10, 2011
- β¦