Wave propagation in a magnetic cylinder

✍ Scribed by P. M. Edwin; B. Roberts

• Publisher: Springer
• Year: 1983
• Tongue: English
• Weight: 639 KB
• Volume: 88
• Category: Article
• ISSN: 0038-0938
• DOI: 10.1007/bf00196186

✦ Synopsis

The nature of oscillations in a magnetic cylinder embedded in a magnetic environment is investigated. It is shown that the standard slender flux tube analysis of a kink mode in a cylinder excludes the possibility of a second mode, which arises under photospheric conditions. Under coronal conditions, two widely separated classes of oscillation can be freely sustained, one on an acoustic time-scale and the other on an Alfvdnic time-scale. The acoustic-type oscillations are always present, but the much shorter period, Alfv6nic-type, oscillations arise only in high density (strictly, low Alfv6n velocity) loops. An application to waves in fibrils is also given, and suggests (following Wentzel, 1979) that they are fast kink waves propagating in a density enhancement. * Formally, ( 14) may be compared with the characteristic period 2L/(mean Alfv6n speed) discussed by Ionson (1982); here the mean speed is %. However, Ionson is concerned with incompressible shear waves whereas we have discussed magnetoacoastic modes.