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Astron. Astrophys. 338, 729-736 (1998)

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Weakly damped Alfvén waves as drivers for spicules

B. De Pontieu and G. Haerendel

Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstrasse, D-85740 Garching bei München, Germany (e-mail: bdp@mpe.mpg.de; hae@mpe.mpg.de)

Received 9 December 1997 / Accepted 29 May 1998

Abstract

We present an analytical model for the damping of Alfvén waves in the partially ionized chromosphere. The damping is due to collisions between ions and neutrals. The ion-neutral collision frequency in this environment is such that the ion and neutral populations are almost perfectly collisionally coupled, leading the Alfvén wave to behave as if it acts on the whole plasma (i.e. including neutrals). The small but finite coupling time between ions and neutrals leads to damping of the Alfvén waves. We find that this type of damping of upward traveling Alfvén waves with frequencies between 0.2 and 0.6 Hz, can cause not only significant heating but also upward motion of the upper chromospheric plasma. In addition the upward force and heating associated with this type of damping can sustain, both dynamically and thermodynamically, an already formed chromospheric spicule. The energy flux carried by the Alfvén waves needed for this type of support of a spicule does not seem to be in contradiction with observational and theoretical evidence for the presence of Alfvén waves in the chromosphere.

Key words: Sun: chromosphere – Sun: transition region – MHD – waves

Send offprint requests to: B. De Pontieu

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© European Southern Observatory (ESO) 1998

Online publication: September 14, 1998
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