9–13 Mar 2015
Albanova, Stockholm
Europe/Stockholm timezone

Global solar dynamo simulation with and without tachocline: a quest for the dynamo location

10 Mar 2015, 12:30
20m
Oskar Klein Auditorium (Albanova, Stockholm)

Oskar Klein Auditorium

Albanova, Stockholm

Speaker

Gustavo Guerrero (Universidade Federal de Minas Gerais)

Description

The solar dynamo, responsible for sunspot formation, is thought to be operating somewhere within the solar interior. Unfortunately, the available observation techniques are not able to observe magnetic field in inner convection zone but only at the solar surface. There are, however, several observational constrains like the cycle period, magnetic field migration or the phase lag between toroidal and poloidal fields, that give us some hints about the solar dynamo location, In this work we contrast the results of global implicit large eddy simulations, with and without tachocline, with these observational links with the aim to identify the most probable mechanism involved in the formation of sunspots. The dynamo models operating in the convection zone only result in a ~2yr cycle period. Their evolution is consistent with dynamo waves migrating upwards in agreement with the Parker-Yoshimura sign rule. Although the upper part or the solar convection zone presents a naturally developed near-surface shear layer (negative at all latitudes), the migration of the magnetic field is poleward. Models that include in the domain a fraction of the radiative zone evolve in a different way due to the development of a tachocline. The intense toroidal magnetic field generated there evolves in a time-scale of the order of decades. It is confined to a sharp region at the interface between radiative and convective zones, however it governs the evolution of the magnetic field of the rest of the domain. The latitudinal shear in the convection zone seems to be only marginally important for the global field generation. These models also develop a near-surface shear layer that makes the magnetic field to migrate towards the equator at the upper part of the domain. The dynamo solution depends on the Rossby number, with results going from steady magnetic fields (with strong poloidal component) for the rapid rotating cases to oscillatory dynamos with long cycle-period for the slow rotating simulations.

Primary author

Gustavo Guerrero (Universidade Federal de Minas Gerais)

Presentation materials