Negative effective magnetic pressure in turbulent convection

Kapyla Petri, petri.kapyla@helsinki.fi, University of Helsinki, Finland
Mantere Maarit, maarit.mantere@helsinki.fi, University of Helsinki
Brandenburg Axel, brandenb@nordita.org, NORDITA
Rogachevskii Igor, gary@bgu.ac.il, Ben-Gurion University of the Negev
Kleeorin Nathan, nat@bgu.ac.il, Ben-Gurion University of the Negev

Abstract
It is generally accepted that the solar dynamo operates in the shear layer beneath the convection zone. This idea faces several difficulties that might be avoided in distributed solar dynamos shaped by near-surface shear. In that scenario, active regions would form due to large-scale (meanfield) instabilities in the near-surface layers. One candidate has been the negative effective magnetic pressure instability (NEMPI). Until recently, this possibility remained uncertain, because it was based on results from mean-field calculations using turbulent transport coefficients determined from direct numerical simulations (DNS). A breakthrough has now been achieved through the direct detection of this instability in idealised forced turbulence simulations. Here we present results from more realistic simulations of highly stratified turbulent convection that represent the near surface layers of the Sun.