Jingade, N and Singh, NK (2020) Mean field dynamo action in shear flows. I: Fixed kinetic helicity. In: Monthly Notices of the Royal Astronomical Society, 495 (4). pp. 4557-4569.
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Abstract
We study mean field dynamo action in a background linear shear flow by employing pulsed renewing flows with fixed kinetic helicity and non-zero correlation time (τ). We use plane shearing waves in terms of time-dependent exact solutions to the Navier¨CStokes equation as derived by Singh and Sridhar (2017). This allows us to self-consistently include the anisotropic effects of shear on the stochastic flow. We determine the average response tensor governing the evolution of mean magnetic field, and study the properties of its eigenvalues that yield the growth rate (γ) and the cycle period (Pcyc) of the mean magnetic field. Both, γ and the wavenumber corresponding to the fastest growing axisymmetric mode vary non-monotonically with shear rate S when τ is comparable to the eddy turnover time T, in which case, we also find quenching of dynamo when shear becomes too strong. When τ/T ∼ O(1), the cycle period (Pcyc) of growing dynamo wave scales with shear as Pcyc ≈ |S|-1 at small shear, and it becomes nearly independent of shear as shear becomes too strong. This asymptotic behaviour at weak and strong shear has implications for magnetic activity cycles of stars in recent observations. Our study thus essentially generalizes the standard αω (or α2ω) dynamo as also the α effect is affected by shear and the modelled random flow has a finite memory. © 2020 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society.
| Item Type: | Journal Article |
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| Publication: | Monthly Notices of the Royal Astronomical Society |
| Publisher: | Oxford University Press |
| Additional Information: | The copyright for this article belongs to the Author(s). |
| Keywords: | Eigenvalues and eigenfunctions; Interactive devices; Shear flow; Stars; Stochastic systems, Cycle periods; Dynamo action; Flow byes; Kinetic helicity; Linear shear flow; Magnetic-field; Mean magnetic field; Mean-field; Star: activity; Zero correlation, Magnetohydrodynamics |
| Department/Centre: | Division of Physical & Mathematical Sciences > Physics |
| Date Deposited: | 23 Jan 2023 12:14 |
| Last Modified: | 23 Jan 2023 12:14 |
| URI: | https://eprints.iisc.ac.in/id/eprint/79287 |
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