LINEAR PERTURBATIONS OF THE BLOCH TYPE OF SPACE-PERIODIC MAGNETOHYDRODYNAMIC STEADY STATES. I. MATHEMATICAL PRELIMINARIES

Мұқаба

Дәйексөз келтіру

Толық мәтін

Аннотация

We consider Bloch eigenmodes in three linear stability problems: the kinematic dynamo problem, the hydrodynamic and MHD stability problem for steady space-periodic flows and MHD states. A Bloch mode is a product of a field of the same periodicity, as the state subjected to perturbation, and a planar harmonic wave, eiq·x. The complex exponential cancels out from the equations of the respective eigenvalue problem, and the wave vector q remains in the equations as a numeric parameter. The resultant problem has a significant advantage from the numerical viewpoint: while the Bloch mode involves two independent spatial scales, its growth rate can be computed in the periodicity box of the perturbed state. The three-dimensional space, where q resides, splits into a number of regions, inside which the growth rate is a smooth function of q. In preparation for a numerical study of the dominant (i.e., the largest over q) growth rates, we have derived expressions for the gradient of the growth rate in q and proven that, for parity-invariant flows and MHD steady states or when the respective eigenvalue of the stability operator is real, half-integer q (whose all components are integer or half-integer) are stationary points of the growth rate. In prior works it was established by asymptotic methods that high spatial scale separation (small q) gives rise to the phenomena of the α-effect or, for parity-invariant steady states, of the eddy diffusivity. We review these findings tailoring them to the prospective numerical applications.

Авторлар туралы

R Chertovskih

Institute of Earthquake Prediction Theory and Mathematical Geophysics Russian academy of sciences

Хат алмасуға жауапты Автор.
Email: vlad@mitp.ru

V Zheligovsky

Institute of Earthquake Prediction Theory and Mathematical Geophysics Russian academy of sciences

Email: vlad@mitp.ru
doctor of physical and mathematical sciences 2009

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© Russian Journal of Earth Sciences, 2023

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