Magnetohydrodynamic Waves in Coronal Magnetostatic Arcades

Details Magnetohydrodynamic Waves in Coronal Magnetostatic Arcades Magnetohydrodynamic Waves in Coronal Magnetostatic Arcades

May 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999apj...517..488t&link_type=abstract

The Astrophysical Journal, Volume 517, Issue 1, pp. 488-496.

Astronomy and Astrophysics

Astronomy

14

Magnetohydrodynamics: Mhd, Sun: Corona, Sun: Magnetic Fields, Waves

Scientific paper

The solar corona is structured by the magnetic field, which has the shape of loops and arcades. These structures remain stable from days to weeks, and there is some evidence, such as sporadic or periodic brightenings detected in UV and soft X-rays, pointing to the existence of periodic oscillations or waves in the corona. Recently Oliver et al. studied, both analytically and numerically, the modes of oscillation of potential and nonpotential magnetic arcades; here we investigate the fast mode properties in a fully magnetostatic arcade (Zweibel & Hundhausen) in which the gravity force is present. The results show that in this equilibrium the fast and slow modes are essentially decoupled and that the spatial structure of the perturbed velocity field is determined by the behavior of the Alfvén speed with height. An arcade in which the Alfvén speed increases with height is characterized by vertically evanescent fast mode solutions. These are the kind of modes that could be more easily detected since their energy is confined within the solar corona. On the other hand, an equilibrium in which the Alfvén speed decreases with height has solutions whose energy tends to escape toward large heights, making difficult the detection of these modes. Also, it is found that the frequencies of fast modes in a nonpotential equilibrium are considerably reduced with respect to the potential case.

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