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Data-Driven 3D Mean-Field MHD Model of Emerging Magnetic Flux and Solar Cycles

Presentation #102.04 in the session Solar Cycle.

Published onSep 18, 2023
Data-Driven 3D Mean-Field MHD Model of Emerging Magnetic Flux and Solar Cycles

We present a new approach to modeling the physical parameters of solar cycles, which combines the Parker-type dynamo theory with modeling the formation and evolution of bipolar magnetic regions (BMR). The goal is to investigate the processes of the initialization of BMR due to the magnetic buoyancy instability in the deep interior to their emergence on the solar surface, and also the effects of the BMR on the global dynamo process. This approach is applied to modeling Solar Cycles 23 and 24. The initialization of BMR is modeled in the framework of Parker’s magnetic buoyancy instability. It defines the depths of BMR injections, which are typically located at the edge of the global dynamo waves. We consider a random distribution of the initial perturbation with longitude and latitude and also the distribution corresponding to the location and size of active regions according to the NOAA database. The tilt of the perturbations is modeled by random function, and the mean tilt is modeled as a near-surface helicity (alpha-effect) term. The modeling results are compared with various observed characteristics of the solar cycles, including the magnetic butterfly diagram, the polar magnetic and basal magnetic fluxes, and the probability distributions of the BMR flux on the surface, as well as helioseismic measurements of the torsional oscillations and meridional circulation. Our results show that BMR can play a significant role in the dynamo processes and affect the strength of the solar cycle. However, the data-driven model shows that the BMR effect alone cannot explain the weak Cycle 24. This weak cycle and the prolonged preceding minimum of magnetic activity were probably caused by a decrease of the turbulent helicity in the bulk of the convection zone during the decaying phase of Cycle 23.

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