  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, 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 and first harmonic, or could
reflect the stage of an overdriven 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 as 2.0 +/- 0.7 G. In contrast,
interpreting the oscillations as a combination of the loop's natural kink
frequency and a harmonious 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.
