The Effect of "Rogue" Active Regions on the Solar Cycle

Abstract

The origin of cycle-to-cycle variations in solar activity is currently the focus of much interest. It has recently been pointed out that large individual active regions with atypical properties can have a significant impact on the long term behaviour of solar activity. We investigate this possibility in more detail using a recently developed 2$\times$2D dynamo model of the solar magnetic cycle. We find that even a single "rogue" bipolar magnetic region (BMR) in the simulations can have a major effect on the further development of solar activity cycles, boosting or suppressing the amplitude of subsequent cycles. In extreme cases an individual BMR can completely halt the dynamo, triggering a grand minimum. Rogue BMRs also have the potential to induce significant hemispheric asymmetries in the solar cycle. To study the effect of rogue BMRs in a more systematic manner, a series of dynamo simulations were conducted, in which a large test BMR was manually introduced in the model at various phases of cycles of different amplitudes. BMRs emerging in the rising phase of a cycle can modify the amplitude of the ongoing cycle while BMRs emerging in later phases will only impact subsequent cycles. In this model, the strongest impact on the subsequent cycle occurs when the rogue BMR emerges around cycle maximum at low latitudes but the BMR does not need to be strictly cross-equatorial. Active regions emerging as far as $20^{\circ }$ from the equator can still have a significant impact. We demonstrate that the combined effect of the magnetic flux, tilt angle and polarity separation of the BMR on the dynamo is via their contribution to the dipole moment, $\delta D_{\mathrm{BMR}}$. Our results indicate that prediction of the amplitude, starting epoch and duration of a cycle requires an accurate accounting of a broad range of active regions emerging in the previous cycle.

References in corpus (13)

• Predicting solar cycle 24 with a solar dynamo model
• Magnetic Properties of Solar Active Regions that Govern Large Solar Flares and Eruptions
• The crucial role of surface magnetic fields for the solar dynamo
• Solar Cycle Propagation, Memory, and Prediction: Insights from a Century of Magnetic Proxies
• Magnetic Flux Transport at the Solar Surface
• Effects of the scatter in sunspot group tilt angles on the large-scale magnetic field at the solar surface
• Predicting the Amplitude and Hemispheric Asymmetry of Solar Cycle 25 with Surface Flux Transport
• Effects of Meridional Flow Variations on Solar Cycles 23 and 24
• Small-Scale and Global Dynamos and the Area and Flux Distributions of Active Regions, Sunspot Groups, and Sunspots: A Multi-Database Study
• Source of a Prominent Poleward Surge During Solar Cycle 24
• The Solar Meridional Circulation and Sunspot Cycle Variability
• Re-examining Sunspot Tilt Angle to Include Anti-Hale Statistics
• A theoretical study of the build-up of the Sun's polar magnetic field by using a 3D kinematic dynamo model

Cited by in corpus (5)

• Nonlinear mechanisms that regulate the solar cycle amplitude
• How good is the bipolar approximation of active regions for surface flux transport?
• A 3D kinematic Babcock Leighton solar dynamo model sustained by dynamic magnetic buoyancy and flux transport processes
• Different contributions to space weather and space climate from different big solar active regions
• The Minimal Helicity of Solar Coronal Magnetic Fields