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Astron. Astrophys. 325, 352-359


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Vertical prominence oscillations and stability

A comparison of the influence of the distant photosphere
in Inverse Polarity and Normal Polarity prominence models

N.A.J. Schutgens

Sterrekundig Instituut Utrecht, Utrecht University, Postbus 80.000, 3508 TA Utrecht, The Netherlands

Received 16 January 1997 / Accepted 24 March 1997

Abstract

All MHD models for prominence equilibrium to date can, in essence, be reduced to two simple current models that describe so-called Inverse (IP) and Normal (NP) Polarity topologies. Using these simple current models, I investigate the influence of the boundary condition provided by the distant photosphere (flux conservation) on vertical prominence oscillations.

The fact that the photosphere is some distance z away from the prominence, implies that the Lorentz force acting on the prominence, due to the photospheric boundary condition, evolves with a delay FORMULA ( FORMULA : coronal Alfvénspeed).

In an earlier paper (Schutgens 1997), it was shown that, in the case of a Kuperus-Raadu (IP) prominence, this delay can greatly influence the vertical stability properties of prominences, especially when FORMULA ( FORMULA : frequency of oscillation, FORMULA ).

In this paper a comparative study is made of this effect in IP and NP prominences.

Because of a different force balance, NP and IP prominences have currents and oscillation periods of different magnitude. The influence of the distant photosphere on NP prominences is minimal, while it has a very pronounced effect on IP prominences. As a result, NP and IP prominences have widely different stability properties. Foot point shaking due to photospheric 5 min. oscillations will only excite IP prominences.

Key words: Sun: prominences - Sun: oscillations - magnetic fields - waves

Send offprint requests to: Nick Schutgens


© European Southern Observatory (ESO) 1997

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