ALFVÉNIC Motions in the Solar Atmosphere
Abstract
The amplitude of bulk velocities associated with upward-propagating Alfve'n waves in the lower solar atmosphere is discussed. We show that for a given wave energy flux, the bulk velocities can be appreciably lower in cases when the wavelength is much larger than the scale height, than in situations where the wavelength is smaller than the scale height. In the chromosphere and lower corona, the former case pertains to waves with dominant timescales of hours, as is found for Alfven waves observed in the solar wind at 1 a.u., or to supergranulation-driven waves with dominant timescales of the order of the supergranular lifetime, 20 hours. This has the important consequence that Alfven waves with energy fluxes of several thousand to a few tens of thousand ergs em 2 -1 at the Sun (such fluxes have been predicted for supergranulation-dnven Alfven waves, and can play a significant role in the dynamics of the solar wind) can have bulk velocity amplitudes 3 km s ' at heights less than 50,000km above the solar limb, if the general solar field strength is at least 2 gauss. Such velocities are consistent with observational limits to bulk velocities in the lower solar atmosphere.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- November 1972
- DOI:
- 10.1086/151703
- Bibcode:
- 1972ApJ...177..255H