Negative magnetic eddy diffusivity due to oscillogenic alpha-effect

• Tipo: Artigo em Revista Científica Internacional
• Data: 2019

Autores

Andrievsky, A (Autor) Outra; Chertovskih, R (Autor) FEUP; Zheligovsky, V (Autor) Outra

Revista

Título: Physica D: Nonlinear Phenomena

Vol. 399

Páginas: 58-72

ISSN: 0167-2789

Editora: Elsevier

Indexação

ISI Web of Knowledge - 2 Citações

Scopus - 2 Citações

Outras Informações

ID Authenticus: P-00Q-FXV

DOI: 10.1016/j.physd.2019.04.005

Abstract (EN): We study large-scale kinematic dynamo action of steady mirror-antisymmetric flows of incompressible fluid, that involve small spatial scales only, by asymptotic methods of the multiscale stability theory. It turns out that, due to the magnetic alpha-effect in such flows, the large-scale mean field experiences harmonic oscillations in time on the scale O(epsilon t) without growth or decay. Here epsilon is the spatial scale ratio and t is the fast time of the order of the flow turnover time. The interaction of the accompanying fluctuating magnetic field with the flow gives rise to an anisotropic magnetic eddy diffusivity, whose dependence on the direction of the large-scale wave vector generically exhibits a singular behaviour, and thus to negative eddy diffusivity for whichever molecular magnetic diffusivity. Consequently, such flows always act as kinematic dynamos on the time scale O(epsilon(2)t); for the directions at which eddy diffusivity is infinite, the large-scale mean-field growth rate is finite on the scale O(epsilon(3/2)t). We investigate numerically this dynamo mechanism for two sample flows.

Idioma: Inglês

Tipo (Avaliação Docente): Científica

Nº de páginas: 15