Turbulence in Stellar Atmospheres

What are the Spatial Scales of Turbulence?

This is an important question because the over-used concept of "microturbulence" does not have a physical basis because photon path-lengths depend on frequency.

What are the physical mechanisms? Acoustic Shocks, magnetohydrodynamic waves?

Turbulence is best studied in the eclipsing binary, zeta Aurigae (K4 Ib), where the physical properties of the atmosphere have been mapped out.

Unpublished calculations with Dr. P. D. Bennett:
The small tangential correlation lengths suggest that the turbulence in this extended atmosphere is of the order or less than the characteristic radial (density) scale-height. This lends credence to the notion that these turbulent motions are related to the puffed up extended atmosphere (as compared to a hydrostatic atmopshere).

Some recent detailed calculations have been made for zeta Aurigae's spectral-type proxy lambda Velorum (K4 II) by the Hamburg group (2003, Boger, Baade, Hegmann & Reimers CS13, p. 1058)