Quasi-biennial oscillations and Rieger-type periodicities in a Babcock–Leighton solar dynamo

¹ Physics and Astronomy Department, University of Florence (FI), 50019, Italy
² Indian Institute of Astrophysics, Koramangala, Bengaluru, 560034 India
³ University College of Science and Technology, Department of Chemical Technology, University of Calcutta, 92, A.P.C. Road, Kolkata, 700009 West Bengal, India
⁴ Department of Physics, Indian Institute of Technology (BHU), Varanasi, 221005 India

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 6 July 2025
Accepted: 24 October 2025

Abstract

Context. The Sun’s magnetic field exhibits the 11 year solar cycle as well as shorter periodicities, popularly known as the quasi-biennial oscillations (QBOs) and Rieger-type periods. Although several theories have been proposed to explain the origin of QBOs and Rieger-type periods, no single theory has had widespread acceptance.

Aims. We explore whether the Babcock–Leighton dynamo can produce Rieger-type periodicity and QBOs and investigate their underlying physical mechanisms.

Methods. We used the observationally guided 3D kinematic Babcock–Leighton dynamo model, which has emerged as a successful model for reproducing many characteristic features of the solar cycle. We used Morlet wavelet and global wavelet power spectrum techniques to analyze the data obtained from the model.

Results. In our model, we report QBOs and Rieger-type periods for the first time. Further, we investigated the individual Babcock–Leighton parameters (fluctuations in flux, latitude, time delay, and tilt scatter) role in the occurrence of QBOs and Rieger-type periods. We find that while fluctuations in the individual parameters of the Babcock–Leighton process can produce QBOs and Rieger-type periodicity, their occurrence probability is enhanced when considering combined fluctuations of all parameters in the Babcock–Leighton process. Finally, we find that with the increase in dynamo supercriticality, the model tends to suppress the generation of Rieger-type periodicity. Thus, this result supports earlier studies that suggest the solar dynamo is not highly supercritical.

Conclusions. The Babcock–Leighton dynamo model successfully reproduces QBOs and Rieger-type periodicities that are observed in various solar activity data.