Astron. Astrophys. 347, 696-710 (1999)

Numerical simulations of spicules driven by weakly-damped Alfvén waves

I. WKB approach

B. De Pontieu  ^*

Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstrasse, D-85740 Garching bei München, Germany (bdp@lmsal.com)

Received 1 September 1998 / Accepted 19 April 1999

Abstract

We present results of time-dependent 1.5 dimensional numerical simulations of the effects that upward travelling Alfvén waves, damped by ion-neutral collisions, have on the chromospheric plasma in a vertical magnetic flux tube. Assuming a rigid flux tube, we use a combination of hydrodynamic equations and a transport equation for the wavelength-averaged wave action density (using the WKB assumption). We find that the damping of a continuous train of upward travelling Alfvén waves with a frequency of 0.5 Hz causes enough upward momentum transfer and heating of the plasma to form structures that are similar to chromospheric spicules in many aspects. We use a non-LTE approximative formula for the hydrogen ionization and assume optically thin radiative losses in the spicular environment. We find that the formed structure reaches a maximum height of 6000 km, temperatures between 8000 to K, electron number densities of the order m^-3 and maximal velocities of about 20 km s^-1. The lifetime of our structure depends on the lifetime of the wave source and can be brought into accordance with observed spicular lifetimes.

Key words: Sun: chromosphere Sun: transition region Magnetohydrodynamics (MHD) waves

* Now at: Lockheed-Martin Solar and Astrophysics Lab, 3251 Hanover St., O/L9-41, Bldg. 252, Palo Alto, CA 94304, USA

This article contains no SIMBAD objects.

Contents

• 1. Introduction
• 2. Equations of the WKB model
• 3. Ionization calculations
• 4. Numerical details
  • 4.1. Numerical integration
  • 4.2. Initial and boundary conditions
• 5. Results
  • 5.1. Continuous wave input
  • 5.2. Waves switched off
• 6. Discussion
• 7. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 1999

Online publication: June 30, 1999
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