The geometry effect on transverse oscillations of coronal loops (Research Note)

In the recent study of nine transversely oscillating coronal loops Verwichte et al. (2004) found that in two events the fundamental mode and the first overtone were observed simultaneously, and the ratio of their periods was different from two predicted by the uniform tube model. This observation inspired Andries et al. (2005a, ApJ, 624, L57) to use this ratio for determining the atmospheric scale height. When doing so these authors assumed that the loop has a semicircular shape. In our paper we address the question how strongly the method suggested by Andries et al. (2005a) depends on the assumed loop shape. We found that this dependence is fairly strong, so that observations of frequencies of the fundamental mode and first overtone have to be supplemented with observations of the loop shape.