  Two approaches are used for description of linear transverse (kink) modes
excited in a vertical thin magnetic flux tube. First one is based on the
elastic thread model (Spruit, 1981). The second one follows from the the Taylor
and Laurent series expansions of wave variables with respect to the tube radius
inside and outside of the magnetic flux tube (Lopin and Nagorny, 2013). It has
been shown that the main reason of the discrepancy of these approaches is
related to the phenomenological equation of plasma motion used in the former
case. This suggests that results obtained on the basis of this equation should
be revised.
