Abstract
Aims: On 13 June 1998, the TRACE satellite was fortuitously well
placed to observe the effects of a flare-induced EIT wave in the corona,
and its subsequent interaction with coronal magnetic loops. In this
study, we use these TRACE observations to corroborate previous
theoretical work, which determined the response of a coronal loop to a
harmonic driver in the context of ideal magnetohydrodynamics, as well as
estimate the magnetic field strength and the degree of longitudinal
inhomogeneity. Methods: Loop edges are tracked, both spatially
and temporally, using wavelet modulus maxima algorithms, with
corresponding loop displacements from its quiescent state analysed by
fitting scaled sinusoidal functions. The physical parameters of the
coronal loop are subsequently determined using seismological techniques.
Results: The studied coronal loop is found to oscillate with two
distinct periods, 501 ± 5 s and 274 ± 7 s, which could be
interpreted as belonging to the fundamental kink mode and first
harmonic, or could reflect the stage of an overdriven loop. Additional
scenarios for explaining the two periods are listed, each resulting in a
different value of the magnetic field and the intrinsic and
sub-resolution properties of the coronal loop. When assuming the periods
belong to the fundamental kink mode and its first harmonic, we obtain a
magnetic field strength inside the oscillating coronal loop of 2.0
± 0.7 G. In contrast, interpreting the oscillations as a
combination of the loop's natural kink frequency and a harmonic EIT wave
provides a magnetic field strength of 5.8 ± 1.5 G. Using the
ratio of the two periods, we find that the gravitational scale height in
the loop is 73 ± 3 Mm. Conclusions: We show that the
observation of two distinct periods in a coronal loop does not
necessarily lead to a unique conclusion. Multiple plausible scenarios
exist, suggesting that both the derived strength of the magnetic field
and the sub-resolution properties of the coronal loop depend entirely on
which interpretation is chosen. The interpretation of the observations
in terms of a combination of the natural kink mode of the coronal loop,
driven by a harmonic EIT wave seems to result in values of the magnetic
field consistent with previous findings. Other interpretations, which
are realistic, such as kink fundamental mode/first harmonic and the
oscillations of two sub-resolution threads result in magnetic field
strengths that are below the average values found before.
Original language | English |
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Pages (from-to) | 13 |
Journal | Astronomy & Astrophysics |
Volume | 534 |
Publication status | Published - 01 Oct 2011 |
Keywords
- magnetohydrodynamics (MHD)
- Sun: corona
- magnetic fields
- Sun: oscillations