The Waldmeier effect and the flux transport solar dynamo

TL;DR

This paper confirms the Waldmeier effect in sunspot data and explores its theoretical explanation using flux transport dynamo models, highlighting the role of meridional circulation fluctuations and turbulent diffusivity.

Contribution

It demonstrates that the Waldmeier effect can be explained by flux transport dynamo models, emphasizing the importance of meridional circulation and turbulent diffusivity in solar cycle irregularities.

Findings

WE2 is a robust result across models and irregularity sources.

WE1 arises from meridional circulation fluctuations in high diffusivity models.

The Waldmeier effect is confirmed in various sunspot datasets.

Abstract

We confirm that the evidence for the Waldmeier effect WE1 (the anti-correlation between rise times of sunspot cycles and their strengths) and the related effect WE2 (the correlation between rise rates of cycles and their strengths) is found in different kinds of sunspot data. We explore whether these effects can be explained theoretically on the basis of the flux transport dynamo models of sunspot cycles. Two sources of irregularities of sunspot cycles are included in our model: fluctuations in the poloidal field generation process and fluctuations in the meridional circulation. We find WE2 to be a robust result which is produced in different kinds of theoretical models for different sources of irregularities. The Waldmeier effect WE1, on the other hand, arises from fluctuations in the meridional circulation and is found only in the theoretical models with reasonably high turbulent diffusivity which ensures that the diffusion time is not more than a few years.