## Numerical simulations of spicules driven by weakly-damped Alfvén waves## I. WKB approach
Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstrasse, D-85740 Garching bei München, Germany (bdp@lmsal.com)
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
* 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
- 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 |