CiteExport$(function(){PrimeFaces.cw("TieredMenu","widget_formSmash_upper_j_idt174",{id:"formSmash:upper:j_idt174",widgetVar:"widget_formSmash_upper_j_idt174",autoDisplay:true,overlay:true,my:"left top",at:"left bottom",trigger:"formSmash:upper:exportLink",triggerEvent:"click"});}); $(function(){PrimeFaces.cw("OverlayPanel","widget_formSmash_upper_j_idt175_j_idt177",{id:"formSmash:upper:j_idt175:j_idt177",widgetVar:"widget_formSmash_upper_j_idt175_j_idt177",target:"formSmash:upper:j_idt175:permLink",showEffect:"blind",hideEffect:"fade",my:"right top",at:"right bottom",showCloseIcon:true});});

Moffatt-drift-driven large-scale dynamo due to a fluctuations with non-zero correlation timesPrimeFaces.cw("AccordionPanel","widget_formSmash_some",{id:"formSmash:some",widgetVar:"widget_formSmash_some",multiple:true}); PrimeFaces.cw("AccordionPanel","widget_formSmash_all",{id:"formSmash:all",widgetVar:"widget_formSmash_all",multiple:true});
function selectAll()
{
var panelSome = $(PrimeFaces.escapeClientId("formSmash:some"));
var panelAll = $(PrimeFaces.escapeClientId("formSmash:all"));
panelAll.toggle();
toggleList(panelSome.get(0).childNodes, panelAll);
toggleList(panelAll.get(0).childNodes, panelAll);
}
/*Toggling the list of authorPanel nodes according to the toggling of the closeable second panel */
function toggleList(childList, panel)
{
var panelWasOpen = (panel.get(0).style.display == 'none');
// console.log('panel was open ' + panelWasOpen);
for (var c = 0; c < childList.length; c++) {
if (childList[c].classList.contains('authorPanel')) {
clickNode(panelWasOpen, childList[c]);
}
}
}
/*nodes have styleClass ui-corner-top if they are expanded and ui-corner-all if they are collapsed */
function clickNode(collapse, child)
{
if (collapse && child.classList.contains('ui-corner-top')) {
// console.log('collapse');
child.click();
}
if (!collapse && child.classList.contains('ui-corner-all')) {
// console.log('expand');
child.click();
}
}
2016 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 798, p. 696-716Article in journal (Refereed) Published
##### Resource type

Text
##### Abstract [en]

##### Place, publisher, year, edition, pages

Cambridge University Press, 2016. Vol. 798, p. 696-716
##### Keywords [en]

dynamo theory, magnetohydrodynamics, turbulence theory
##### National Category

Fusion, Plasma and Space Physics
##### Identifiers

URN: urn:nbn:se:kth:diva-189362DOI: 10.1017/jfm.2016.284ISI: 000377447400031OAI: oai:DiVA.org:kth-189362DiVA, id: diva2:948288
#####

PrimeFaces.cw("AccordionPanel","widget_formSmash_j_idt487",{id:"formSmash:j_idt487",widgetVar:"widget_formSmash_j_idt487",multiple:true});
#####

PrimeFaces.cw("AccordionPanel","widget_formSmash_j_idt493",{id:"formSmash:j_idt493",widgetVar:"widget_formSmash_j_idt493",multiple:true});
#####

PrimeFaces.cw("AccordionPanel","widget_formSmash_j_idt499",{id:"formSmash:j_idt499",widgetVar:"widget_formSmash_j_idt499",multiple:true});
##### Note

We present a theory of large-scale dynamo action in a turbulent flow that has stochastic, zero-mean fluctuations of the a parameter. Particularly interesting is the possibility of the growth of the mean magnetic field due to Moffatt drift, which is expected to he finite in a statistically anisotropic turbulence. We extend the Kraichnan Moffatt model to explore effects of finite memory of a fluctuations, in a spirit similar to that of Sridhar & Singh (Mon. Not. R. Astron. Soc., vol. 445, 2014, pp. 3770-3787). Using the first-order smoothing approximation, we derive a linear integro-differential equation governing the dynamics of the large-scale magnetic field, which is non-perturbative in the alpha-correlation time tau(alpha), We recover earlier results in the exactly solvable white-noise limit where the Moffatt drift does not contribute to the dynamo growth/decay. To study finite-memory effects, we reduce the integro-differential equation to a partial differential equation by assuming that tau(alpha). be small but non-zero and the large-scale magnetic field is slowly varying. We derive the dispersion relation and provide an explicit expression for the growth rate as a function of four independent parameters. When tau(alpha) not equal 0, we find that: (i) in the absence of the Moffatt drift, but with finite Kraichnan diffusivity, only strong a fluctuations can enable alpha mean-field dynamo (this is qualitatively similar to the white-noise case); (ii) in the general case when also the Moffatt drift is non-zero, both weak and strong a fluctuations can lead to a large-scale dynamo; and (iii) there always exists a wavenumber (k) cutoff at sonic large k beyond which the growth rate turns negative, irrespective of weak or strong a fluctuations. Thus we show that a finite Moffatt drift can always facilitate large-scale dynamo action if sufficiently strong, even in the case of weak alpha fluctuations, and the maximum growth occurs at intermediate wavenumbers.

QC 20160711

Available from: 2016-07-11 Created: 2016-07-04 Last updated: 2017-11-28Bibliographically approved
doi
urn-nbn$(function(){PrimeFaces.cw("Tooltip","widget_formSmash_j_idt1221",{id:"formSmash:j_idt1221",widgetVar:"widget_formSmash_j_idt1221",showEffect:"fade",hideEffect:"fade",showDelay:500,hideDelay:300,target:"formSmash:altmetricDiv"});});

CiteExport$(function(){PrimeFaces.cw("TieredMenu","widget_formSmash_lower_j_idt1275",{id:"formSmash:lower:j_idt1275",widgetVar:"widget_formSmash_lower_j_idt1275",autoDisplay:true,overlay:true,my:"left top",at:"left bottom",trigger:"formSmash:lower:exportLink",triggerEvent:"click"});}); $(function(){PrimeFaces.cw("OverlayPanel","widget_formSmash_lower_j_idt1276_j_idt1278",{id:"formSmash:lower:j_idt1276:j_idt1278",widgetVar:"widget_formSmash_lower_j_idt1276_j_idt1278",target:"formSmash:lower:j_idt1276:permLink",showEffect:"blind",hideEffect:"fade",my:"right top",at:"right bottom",showCloseIcon:true});});