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Seismology of coronal loops using observations of damped transverseoscillations in combination with results from theoretical models is a tool toindirectly infer physical parameters in the solar atmospheric plasma. Existingseismology schemes based on approximations to the period and damping time ofkink oscillations are often used beyond their theoretical range ofapplicability. These approximations assume that the variation of density acrossthe loop is confined to a nonuniform layer much thinner than the radius of theloop, but the results of the inversion problem often do not satisfy thispreliminary hypothesis. Here, we determine the accuracy of the analyticapproximations to the period and damping time, and its impact on seismologyestimates, when largely nonuniform loops are considered. We find that theaccuracy of the approximations when used beyond their range of applicability isstrongly affected by the form of the density profile across the loop, that isobservationally unknown and so must be arbitrarily imposed as part of thetheoretical model. The error associated with the analytic approximations can belarger than 50% even for relatively thin nonuniform layers. This error directlyaffects the accuracy of approximate seismology estimates compared to actualnumerical inversions. In addition, assuming different density profiles canproduce noncoincident intervals of the seismic variables in inversions of thesame event. The ignorance about the true shape of density variation across theloop is an important source of error that may dispute the reliability ofparameters seismically inferred assuming an ad hoc density profile.

The behavior of transverse waves in nonuniform solar flux tubes. II. Implications for coronal loop seismology