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)
