@article{9cb7ffac7a9b4b479ed959c7a7c0dc5b,
title = "Sharp magnetic structures from dynamos with density stratification",
abstract = "Recent direct numerical simulations (DNS) of large-scale turbulent dynamos in strongly stratified layers have resulted in surprisingly sharp bipolar structures at the surface. Here, we present new DNS of helically and non-helically forced turbulence with and without rotation and compare with corresponding mean-field simulations (MFS) to show that these structures are a generic outcome of a broader class of dynamos in density-stratified layers. The MFS agree qualitatively with the DNS, but the period of oscillations tends to be longer in the DNS. In both DNS and MFS, the sharp structures are produced by converging flows at the surface and might be driven in non-linear stage of evolution by the Lorentz force associated with the large-scale dynamo-driven magnetic field if the dynamo number is at least 2.5 times supercritical.",
keywords = "Dynamo, Sunspots, Turbulence",
author = "Sarah Jabbari and Axel Brandenburg and Nathan Kleeorin and Igor Rogachevskii",
note = "Funding Information: the Swedish National Allocations Committee at the Center for Parallel Computers at the Royal Institute of Technology in Stockholm. This work utilized the Janus supercomputer, which is supported by the National Science Foundation (award number CNS-0821794), the University of Colorado Boulder, the University of Colorado Denver and the National Center for Atmospheric Research. The Janus supercomputer is operated by the University of Colorado Boulder. Funding Information: We thank Dhrubaditya Mitra for useful discussions regarding this work. It was supported in part by the Swedish Research Council Grants No. 621-2011-5076 (AB, SJ), 2012-5797 (AB), Australian Research Council{\textquoteright}s Discovery Projects funding scheme project no. DP160100746 (SJ) and the Research Council of Norway under the FRINATEK grant 231444 (AB, IR). It was also supported by The Royal Swedish Academy of Sciences grant no. AST2016-0026 (SJ). We acknowledge the allocation of computing resources provided by Publisher Copyright: {\textcopyright} 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society",
year = "2017",
month = jun,
day = "1",
doi = "10.1093/mnras/stx148",
language = "English",
volume = "467",
pages = "2753--2765",
journal = "Monthly Notices of the Royal Astronomical Society",
issn = "0035-8711",
publisher = "Oxford University Press",
number = "3",
}