Speaker
Description
The magnetohydrodynamic dynamo effect, which governs the interactions between internal solar fluid flows and magnetic fields, drives the Sun’s 11-year activity cycle. The meridional circulation, a key aspect of this process, plays a crucial role in regulating the solar cycle and its large-scale magnetic field, particularly within the framework of flux transport dynamo models. However, the deep internal profile of this large-scale flow remains challenging to observe, poorly constrained, and heavily debated.
In this work, we use the evolution of the Sun’s surface magnetic flux to constrain the internal profile of the meridional circulation. To achieve this, we developed a highly flexible basis of nearly orthogonal functions constructed from Legendre and Chebyshev polynomials to describe the latitu- dinal and radial dependencies of the flow, enabling the generation of complex circulation geometries. By combining these functions with weights optimized via a genetic algorithm, this versatile frame- work can adequately reproduce most kinematic profiles used in existing dynamo models, as well as more complex multicellular flow patterns, including, for example, small secondary flow cells located in depth and/or latitude.
Building on this mathematical foundation, we formulate an inversion problem to map the inter- nal meridional flow in a Babcock-Leighton flux transport dynamo model. Using a robust genetic algorithm, the flow is inverted by constraining the time-latitude structure of the deep toroidal mag- netic field to fit the shape of the observed surface butterfly diagram, and the surface magnetograms produced by our model to fit observed surface magnetic data.
This optimization process explores a complex, multimodal parameter space to identify not merely a single optimal parameter set, but rather a remarkably diverse population of statistically acceptable meridional circulation profiles. Notably, this ensemble includes complex, multiple-cell circulation patterns. Despite their internal topological differences, all accepted profiles successfully reproduce the fundamental characteristics of solar magnetism and match observed surface data. These results highlight the intrinsic degeneracy in inferring deep solar flows from surface magnetic evolution. Consequences for dynamo-based solar cycle prediction schemes will be briefly discussed.