Longitudinal Oscillations in Density Stratified and Expanding Solar Waveguides
Abstract
Waves and oscillations can provide vital information about the internal structure of waveguides in which they propagate. Here, we analytically investigate the effects of density and magnetic stratification on linear longitudinal magnetohydrodynamic (MHD) waves. The focus of this paper is to study the eigenmodes of these oscillations. It is our specific aim to understand what happens to these MHD waves generated in flux tubes with nonconstant (e.g., expanding or magnetic bottle) crosssectional area and density variations. The governing equation of the longitudinal mode is derived and solved analytically and numerically. In particular, the limit of the thin flux tube approximation is examined. The general solution describing the slow longitudinal MHD waves in an expanding magnetic flux tube with constant density is found. Longitudinal MHD waves in density stratified loops with constant magnetic field are also analyzed. From analytical solutions, the frequency ratio of the first overtone and fundamental mode is investigated in stratified waveguides. For small expansion, a linear dependence between the frequency ratio and the expansion factor is found. From numerical calculations it was found that the frequency ratio strongly depends on the density profile chosen and, in general, the numerical results are in agreement with the analytical results. The relevance of these results for solar magnetoseismology is discussed.
 Publication:

The Astrophysical Journal
 Pub Date:
 April 2012
 DOI:
 10.1088/0004637X/748/2/110
 arXiv:
 arXiv:1204.4201
 Bibcode:
 2012ApJ...748..110L
 Keywords:

 magnetohydrodynamics: MHD;
 Sun: chromosphere;
 Sun: corona;
 Sun: oscillations;
 waves;
 Astrophysics  Solar and Stellar Astrophysics
 EPrint:
 10 pages, 5 figures, published in ApJ, uses emulateapj