Nature of Grand Minima and Maxima from Fully Non-Linear Flux-Transport Dynamos

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Thursday, September 7, 2017

We aim to investigate the nature and occurrence characteristics of grand solar minimum and maximum periods, which are observed in the solar proxy records such as 10Be and 14C, using a fully non-linear Babcock-Leighton type flux transport dynamo including momentum and entropy equations.

Maximum toroidal magnetic field strength image
The top panel shows the maximum toroidal magnetic field strength at the base of the convection zone (0.71 R). The blue and red fill colours represent identified grand minima and maxima, respectively. The bottom panel shows the butterfy diagram (toroidal magnetic field at base of convection zone) for the grand minimum period between 5380 and 5420 years, marked with a blue star in the top panel.

The differential rotation and meridional circulation are generated from the effect of turbulent Reynolds stress and are subjected to back-reaction from the magnetic field. To generate grand minimum and maximum-like periods in our simulations, we used random fluctuations in the angular momentum transport process, namely the Lambda-mechanism, and in the Babcock-Leighton mechanism. To characterise the nature and occurrences of the identified grand minima and maxima in our simulations, we used the waiting time distribution analyses, which reflects whether the underlying distribution arises from a random or a memory-bearing process. The results show that, in majority of the cases, the distributions of grand minima and maxima reveal that the nature of these events originates from memoryless processes. We also found that in our simulations the meridional circulation speed tends to be smaller during grand maximum, while it is faster during grand minimum periods. The radial differential rotation on the other hand tend to be larger during grand grand maxima, while it is smaller during grand minima.

Publication Name: Astrophysical Journal