Title:	Mean field dynamo action in shear flows. I: fixed kinetic helicity
Authors:	Jingade, Naveen Singh, Nishant K.
Keywords:	dynamo magnetic fields MHD plasmas turbulence stars: activity
Issue Date:	Jul-2020
Publisher:	Oxford University Press on behalf of the Royal Astronomical Society
Citation:	Monthly Notices of the Royal Astronomical Society, 2020, Vol.495, p4557–4569
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-Stokes equation as derived by Singh & 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.
Description:	Open Access
URI:	http://hdl.handle.net/2289/7500
ISSN:	0035-8711 1365-2966 (online)
Alternative Location:	https://ui.adsabs.harvard.edu/abs/2020MNRAS.495.4557J/abstract https://arxiv.org/abs/1911.00235 https://doi.org/10.1093/mnras/staa1204
Copyright:	2020 The Author(s)
Appears in Collections:	Research Papers (A&A)

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