# Understanding solar cycle variability

## TL;DR

This paper presents a normal-form dynamo model that explains solar cycle variability, including grand minima, by combining dynamo theory with empirical data, providing a unified understanding of solar magnetic activity fluctuations.

## Contribution

It introduces a normal-form model constrained by observations that captures solar cycle variability and grand minima, validated against Babcock-Leighton dynamo models.

## Key findings

- Model reproduces solar activity variations from decades to millennia.
- Successfully explains occurrence of grand minima.
- Aligns with results from Babcock-Leighton dynamo models.

## Abstract

The level of solar magnetic activity, as exemplified by the number of sunspots and by energetic events in the corona, varies on a wide range of time scales. Most prominent is the 11-year solar cycle, which is significantly modulated on longer time scales. Drawing from dynamo theory together with empirical results of past solar activity and of similar phenomena on solar-like stars, we show that the variability of the solar cycle can be essentially understood in terms of a weakly nonlinear limit cycle affected by random noise. In contrast to ad-hoc `toy models' for the solar cycle, this leads to a generic normal-form model, whose parameters are all constrained by observations. The model reproduces the characteristics of the variable solar activity on time scales between decades and millennia, including the occurrence and statistics of extended periods of very low activity (grand minima). Comparison with results obtained with a Babcock-Leighton-type dynamo model confirms the validity of the normal-mode approach.