Dynamo model for grand maxima of solar activity: can superflares occur on the Sun?

TL;DR

This paper presents a solar dynamo model with fluctuating parameters to explain grand maxima of solar activity and assesses the potential for superflares on the Sun, concluding such superflares are extremely unlikely.

Contribution

It introduces a dynamo model with fluctuating alpha-effect to explain grand maxima and evaluates the likelihood of superflares occurring on the Sun.

Findings

Grand activity maxima can result from fluctuations reversing the alpha-effect sign.

The model produces cycles with magnetic energies hundreds of times larger than normal.

The probability of superflares on the Sun is estimated to be extremely low.

Abstract

Recent data on superflares on sun-like stars and radiocarbon data on solar activity in the past are both indicative of transient epochs of unusually high magnetic activity. We propose an explanation for the grand activity maxima in the framework of a solar dynamo model with fluctuating parameters. Solar-type dynamos are oscillatory because of the combination of the solar-type differential rotation with positive (in the Northern hemisphere) alpha-effect. An artificial reversal of the sign in the alpha-effect changes the dynamo to a steady regime with hundreds of times larger magnetic energy compared to the amplitude of the cyclic dynamo. Sufficiently large and durable fluctuations reversing the sign of the alpha-effect during the growth phase of a magnetic cycle can, therefore, cause a transient change to a steady dynamo with considerably increased magnetic energy. This qualitative scenario for grand activity maxima is supported by computations of the dynamo model with a fluctuating alpha-effect. The computed statistics of several thousand magnetic cycles gives examples of cycles with very high magnetic energy. Our preliminary estimations, however, suggest that the probability of solar superflares is extremely low.