Tilt of the Bipolar Active Regions: Beyond Joy’s Law
The tilt of bipolar magnetic regions (BMRs) plays a pivotal role in the Babcock–Leighton mechanism responsible for generating the Sun's poloidal magnetic field. Building upon the prior work conducted by Jha et al. (2020), we have undertaken an extended analysis of BMR data tracked during the Michelson Doppler Imager mission (1996–2011) and the Helioseismic and Magnetic Imager mission (2010–2018). Our aim was to gain a robust insight into how the magnetic field characteristics influence BMR tilts. Our investigation reveals a notable relationship between the strength of the maximum magnetic field (Bmax) in BMRs and the slope of Joy's law (γ0) Initially, as Bmax rises, γ0 exhibits gradual growth. However, an intriguing trend emerges when Bmax surpasses 2 kG: γ0 starts to decrease. This decline in observed γ0 with increasing Bmax suggests the possibility of nonlinear tilt quenching within the Babcock–Leighton process. Additionally, our analysis uncovers a noteworthy correlation between the scatter of BMR tilts around Joy's law and the magnitude of Bmax. As BMRs grow, they appear to be less affected by convective forces, resulting in a systematic reduction in the scatter of their tilts. Recently we have further extended this work by tracking the BMRs using our newly developed algorithm AutoTAB, over their lifetime to get better insight into the BMRs evolution.
Dr. Bibhuti Kumar Jha got his PhD from Indian Institute of Astrophysics, Bangalore, India in 2022, and his thesis was on the "Long-term study of the Sun and its implication to solar dynamo models”. Currently, he is a Post-Doctoral Researcher at Southwest Research Institute, Boulder, CO, and working on incorporating the far-side helioseismic observations of AR in the Surface Flux Transport model. His research interests include development of automatic algorithms, surface flux transport models, Machine Learning etc. He is also interested in public outreach activity, teaching, and photography.