Numerical simulations of spicules driven by weakly-damped Alfvén waves. I. WKB approach
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 12 000 K, electron number densities of the order 10(17) 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.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- July 1999
- Bibcode:
- 1999A&A...347..696D
- Keywords:
-
- SUN: CHROMOSPHERE;
- SUN: TRANSITION REGION;
- MAGNETOHYDRODYNAMICS (MHD);
- WAVES