Letter to the Editor

Non-axisymmetric spherical interface dynamos

¹ Department of Mathematical Sciences, Laver Building, University of Exeter, EX4 4QE, UK e-mail: kzhang@ex.ac.uk
² Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030, PR China

Received: 4 June 2004
Accepted: 12 July 2004

Abstract

A fully three-dimensional, nonlinear, time-dependent spherical interface dynamo with a solar-like internal differential rotation and a single-cell meridional circulation is investigated. There are four regions in our interface dynamo model: a uniformly rotating core, a thin differentially rotating tachocline, a turbulent convection zone and a nearly insulating exterior. The different regions are coupled by the electric and magnetic matching conditions at the interfaces. For the first time, non-axisymmetric spherical nonlinear interface dynamos are found. When the magnetic Reynolds number based on the differential rotation is small or when the effect of the meridional circulation is substantial, we show that the spherical interface dynamos are non-axisymmetric even though the α-distribution, differential rotation and meridional circulation are all axisymmetric. Implication of the results for the solar dynamo is discussed.