Context :

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 { \pm } 5 s and 274 { \pm } 7 s , which could be interpreted as belonging to the fundamental 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 as 2.0 { \pm } 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 { \pm } 1.5 G. Using the ratio of the two periods , we find that the gravitational scale height in the loop is 73 { \pm } 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 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 .