## 1. IntroductionIt is now a well known result of helioseismology that the radiative
part of the Sun rotates almost as a solid body, at least down to
( A step forward was taken recently by Zahn et al. (1997) (which will be referred to as ZTM) and by Kumar & Quataert (1997) when they examined the role of the gravity waves generated at the base of the convective zone. They found that such waves transport momentum "non-locally" on a rather short timescale, and that they tend to flatten the rotation profile. Let us recall briefly the somewhat different approaches used by the
two groups. Gravity waves conserve their momentum as long as they are
not damped. Thus when assuming that both prograde (
) and retrograde ( ) waves
are excited with the same intensity at the base of the convective
region, differential damping is required in order to get a net deposit
of momentum. This differential damping will be provided by the Doppler
shift due to differential rotation, since radiative damping varies as
(where is the local
frequency). Zahn et al. consider only the damping in the critical
layer where this local frequency goes to zero. There the waves are
completely damped, and they deposit the totality of their momentum. At
the same time, the frequency of their
counterparts increases, diminishing their damping. Thus they will be
able to travel all the way to the core and back, to be re-absorbed by
the convective zone
However in this first numerical study, we keep only the transport of angular momentum by the waves which are completely damped in their critical layer. This contribution will be added to that due to meridional circulation and shear turbulence. © European Southern Observatory (ESO) 1998 Online publication: November 24, 1997 |