Alleviating α quenching by solar wind and meridional flows

¹ NORDITA, AlbaNova University Center, Roslagstullsbacken 23, 10691 Stockholm, Sweden
e-mail: dhruba.mitra@gmail.com
² School of Mathematics, University of Manchester, Oxford Road, Manchester M13 9PL, UK
³ Astronomy Unit, School of Mathematical Sciences, Queen Mary University of London, Mile End Road, London E1 4NS, UK
⁴ Department of Astronomy, Stockholm University, 10691 Stockholm, Sweden

Received: 25 August 2010
Accepted: 1 December 2010

Abstract

Aims. We study the ability of magnetic helicity expulsion to alleviate catastrophic α-quenching in mean field dynamos in two–dimensional spherical wedge domains.

Methods. Motivated by the physical state of the outer regions of the Sun, we consider α²Ω mean field models with a dynamical α quenching. We include two mechanisms which have the potential to facilitate helicity expulsion, namely advection by a mean flow (“solar wind”) and meridional circulation.

Results. We find that a wind alone can prevent catastrophic quenching, with the field saturating at finite amplitude. In certain parameter ranges, the presence of a large-scale meridional circulation can reinforce this alleviation. However, the saturated field strengths are typically below the equipartition field strength. We discuss possible mechanisms that might increase the saturated field.