The sun is a magnetic star whose variable activity has a profound effect on our technological society. The high speed solar wind and its energetic particles, mass ejections and flares that affect the solar-terrestrial interaction all stem from the variability of the underlying solar magnetic fields. We are in an era of fundamental discovery about the overall dynamics of the solar interior and its ability to generate magnetic fields through dynamo action. This has come about partly through guidance and challenges to theory from helioseismology as we now observationally probe the interior of this star. It also rests on our increasing ability to conduct simulations of the crucial solar turbulent processes using the latest generation of supercomputers.

Introduction

The intensely turbulent convection zone of the sun, occupying the outer 30% by radius or 200Mm in depth, exhibits some remarkable dynamical properties that have largely defied theoretical explanation. The most central issues concern the difierential rotation with radius and latitude that is established by the convection redistributing angular momentum, and the manner in which the sun achieves its 22-year cycles of magnetic activity. These dynamical issues are closely linked: the global dynamo action is most likely very sensitive to the angular velocity Ω profiles realized within the sun. It is striking that the underlying solar turbulence can be both highly intermittent and chaotic on the smaller spatial and temporal scales, and yet achieve a large-scale order that is robust in character (e.g. Brummell, Cattaneo & Toomre 1995).