Oscillations in an active region filament: Observations and comparison with MHD waves

TitleOscillations in an active region filament: Observations and comparison with MHD waves
Publication TypeJournal Article
Year of Publication2001
AuthorsRégnier, S., Solomon J., and Vial J. C.
JournalAstronomy and Astrophysics
Date PublishedSep

During the MEDOC Campaign 4, on October 1999, observations of a solar active region filament were carried out by the SUMER/SoHO spectrometer. A time sequence of this filament has been obtained with a duration of 7 h 30 min and with a temporal resolution of 30 s. The Fourier analysis of the line-of-sight Doppler velocities measured in the 584.33 Å HeI line allows us to detect oscillations in several ranges of periodicities (short periods: less than 5 min, intermediate periods: 6-20 min, and long periods: greater than 40 min). From a theoretical point of view, we consider the possible modes of oscillations of an active region filament. Following $\backslash$cite$\{$joa93a$\}$, we treat the filament as a plasma slab embedded in a uniform magnetic field inclined at an angle phi to the long axis of the slab. Solving the dispersion equations for Alfvén waves and magnetoacoustic waves, primary and secondary mode frequencies appear to be non-equidistant. For the comparison between the observed and calculated frequencies, we outline an identification method of the oscillation modes in the observed filament. This identification provides a diagnostic of the filament: the angle between the magnetic field and the long axis of the slab is estimated to be 18$^{deg}$, and the magnetic field strength B (G) is proportional to the square root of the density rho$_{o}$ (cm$^{-3}$) in the slab, B \~ 2.9 x 10$^{-5}$ sqrt $\{$rho$_{o}$$\}$.