Issue |
A&A
Volume 369, Number 1, April I 2001
|
|
---|---|---|
Page(s) | 323 - 328 | |
Section | Astronomical instrumentation | |
DOI | https://doi.org/10.1051/0004-6361:20010087 | |
Published online | 15 April 2001 |
Nonlocal dynamo waves in a turbulent shear flow
1
Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
2
A.F. Ioffe Institute of Physics and Technology, 194021 St. Petersburg, Russia
Corresponding author: G. Rüdiger, gruediger@aip.de
Received:
22
September
2000
Accepted:
12
January
2001
The turbulent dynamo action in a shear flow is considered by making
use of a quasilinear approximation and neglecting the back-reaction of a
generated magnetic field on turbulence. The shear can stretch turbulent
magnetic field lines in such a way that turbulent motions may become
suitable for the generation of a large-scale magnetic field even in the
absence of any stratification. There is no α-effect present in our
computations.
The nonlocal integral representation for the mean electromotive force is derived,
which is valid even if the turbulent length scale is comparable to
that of the mean field. The basic result is that the presence of
shear changes the type of the equation governing the mean magnetic
field so that the latter indeed can be generated even in the absence of
rotation or large-scale stratification of turbulence. To this end,
however, if the turbulence field has a monotonously falling
("turbulence-type") spectrum, a rather strong shear is needed. For
Kepler disks the instability condition reads , which might be fulfilled in the transition
layers between star and disk. A system, on the other hand, consisting
of random waves, large-scale magnetic fields and mean-field shear
flow can never be stable.
Key words: magnetohydrodynamics / stars: magnetic fields / interstellar medium: magnetic fields / accretion, accretion discs
© ESO, 2001
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