A Babcock-Leighton solar dynamo model with multi-cellular meridional circulation in advection- and diffusion-dominated regimes

Abstract:

Babcock-Leighton type solar dynamo models with single cell
meridional circulation are successful in reproducing many solar
cycle features, and recently such a model was applied for solar
cycle 24 amplitude prediction. It seems that cycle 24 amplitude
forecast may not be validated. One of the reasons is the assumption
of a single cell meridional circulation. Recent observations and
theoretical models of meridional circulation do not indicate a single-celled
flow pattern. So it is nessecary to examine the role of complex
multi-cellular circulation patterns in a Babcock-Leighton solar
dynamo model in the advection and diffusion dominated regimes.
By simulating a Babcock-Leighton solar dynamo model with multi-cellular
flow, we show that the presence of a weak, second, high-latitude
reverse cell speeds up the cycle and slighty enhances the poleward branch
in the butterfly diagram, whereas the presence of a second cell
in depth reverses the tilt of the butterfly wing and leads to an
anti-solar type feature. If, instead, the butterfly diagram is
constructed from the middle of the convection zone in that case,
a solar-like pattern can be retrieved. All the above cases behave
qualitatively similar in advection and diffusion-dominated regimes.
However, our dynamo with a meridional circulation containing four
cells in latitude behaves distinctly different in the two regimes,
producing a solar-like butterfly diagram with fast cycles in
diffusion-dominated regime, and a complex branches in the butterfly
diagram in the advection-dominated regime. Another interesting
finding from our studies is that a four-celled flow pattern
containing two in radius and two in latitude always produces
quadrupolar parity as the relaxed solution.