Transverse Oscillations of Longitudinally Stratified Coronal Loops with Variable Cross Section

Michael S. Ruderman, Gary Verth, Robert Erdélyi

Research output: Contribution to journalArticlepeer-review

88 Citations (Scopus)

Abstract

We consider transverse oscillations of coronal loops that have both variable circular cross-sectional area and plasma density in the longitudinal direction. The primary focus of this paper is to study the eigenmodes of these oscillations. Implementing the method of asymptotic expansions with the ratio of the loop radius to length as a small parameter, a second-order ordinary differential equation is derived describing the displacement of the loop axis. Together with the boundary conditions at the tube ends that follow from the frozen-in condition, this equation constitutes the Sturm-Liouville problem determining the eigenfrequencies and eigenmodes. Our results are relevant to the magnetoseismological method of estimating the coronal density scale height by using the observed ratio of the fundamental frequency and first overtone of loop kink oscillations. It is shown that this method is very sensitive to the tube expansion factor, which is the ratio of the tube radii at the apex and footpoints. The estimated scale height is a monotonically decreasing function of the expansion factor.
Original languageEnglish
Pages (from-to)694-700
JournalThe Astrophysical Journal
Volume686
Issue number1
DOIs
Publication statusPublished - Oct 2010

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