Stretching of the toroidal field and generation of magnetosonic waves in differentially rotating plasma

¹ INAF, Osservatorio Astrofisico di Catania, via S. Sofia 78, 95123 Catania, Italy e-mail: abo@oact.inaf.it
² INFN, Sezione di Catania, via S. Sofia 72, 95123 Catania, Italy
³ A.F.Ioffe Institute of Physics and Technology and Isaac Newton Institute of Chile, Branch in St. Petersburg, 194021 St. Petersburg, Russia

Received: 26 April 2007
Accepted: 18 July 2007

Abstract

Aims.We evaluate the generation of magnetosonic waves in differentially rotating magnetized plasma.

Methods.Differential rotation leads to an increase of the azimuthal field by winding up the poloidal field lines into the toroidal field lines. An amplification of weak seed perturbations is considered in this time-dependent background state.

Results.It is shown that seed perturbations can be amplified by several orders of magnitude in a differentially rotating flow. The only necessary condition for this amplification is the presence of a non-vanishing component of the magnetic field in the direction of the angular velocity gradient.