Astronomy and Astrophysics – Astrophysics
Scientific paper
2003-03-27
Astron.Astrophys. 408 (2003) 401-408
Astronomy and Astrophysics
Astrophysics
8 pages, 9 figures, accepted for publication (18.03.2003) in the "Astronomy and Astrophysics"
Scientific paper
10.1051/0004-6361:20030454
Recently it was found that helical magnetized flows efficiently amplify Alfv\'en waves (Rogava et al. 2003, A&A, v.399, p.421). This robust and manifold nonmodal effect was found to involve regimes of transient algebraic growth (for purely ejectional flows), and exponential instabilities of both usual and parametric nature. However the study was made in the incompressible limit and an important question remained open - whether this amplification is inherent to swirling MHD flows per se and what is the degree of its dependence on the incompressibility condition. In this paper, in order to clear up this important question, we consider full compressible spectrum of MHD modes: Alfv\'en waves (AW), slow magnetosonic waves (SMW) and fast magnetosonic waves (FMW). We find that helical flows inseparably blend these waves with each other and make them unstable, creating the efficient energy transfer from the mean flow to the waves. The possible role of these instabilities for the onset of the MHD turbulence, self-heating of the flow and the overall dynamics of astrophysical flows are discussed.
Bodo Gianluigi
Massalgia Silvano
Osmanov Zaza
Rogava Andria
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