Role of longitudinal activity complexes for solar and stellar dynamos

TL;DR

This paper investigates the physical mechanisms behind magnetic activity concentrations in the Sun and stars, exploring observational evidence, theoretical models, and dynamo simulations to understand their origin and behavior.

Contribution

It introduces non-axisymmetric mean-field dynamo models and pure alpha-squared models, highlighting their potential to explain observed magnetic activity patterns and dynamics.

Findings

Identification of longitudinal magnetic activity concentrations in the Sun and stars.

Development of non-axisymmetric dynamo models matching observational features.

Demonstration of time-dependent dynamo behavior including azimuthal waves and oscillations.

Abstract

In this paper we first discuss observational evidence of longitudinal concentrations of magnetic activity in the Sun and rapidly rotating late-type stars with outer convective envelopes. Scenarios arising from the idea of rotationally influenced anisotropic convective turbulence being the key physical process generating these structures are then presented and discussed - such effects include the turbulent dynamo mechanism, negative effective magnetic pressure instability (NEMPI) and hydrodynamical vortex instability. Finally, we discuss non-axisymmetric stellar mean-field dynamo models, the results obtained with them, and compare those with the observational information gathered up so far. We also present results from a pure alpha-squared mean-field dynamo model, which show that time-dependent behavior of the dynamo solutions can occur both in the form of an azimuthal dynamo wave and/or oscillatory behavior related to the alternating energy levels of the active longitudes.