SOLARNET Conference: The Many Scales of the Magnetic Sun

The Bipolar Magnetic Regions (BMRs) are the strong magnetic feature, consisting of two magnetic polarities separated by a neutral line, observed on the surface of the Sun. They are found to be tilted with the equatorial line, which statistically increases with their latitudes, this is popularly known as Joy’s Law. The thin flux tube model suggests that the magnetic field concentrated in flux tubes rises from the base of the convection zone to emerge as BMRs on the surface. As flux tubes rise, torque induced by the Coriolis force acting on diverging flows developed at the apex of tubes produces the tilt in the BMRs. Despite the popularity of the rising flux tube model as an explanation for the formation of BMRs, observational support is limited. In this work, we study the evolving properties of BMR throughout their lifetimes by analyzing line-of-sight magnetograms from Michelson Doppler Imager (MDI) and Helioseismic and Magnetic Imager (HMI) for the past two solar cycles. Our analysis employs an automatic detection algorithm and an in-house developed automatic algorithm for tracking the BMRs to study their evolution. The evolutions of BMR tilt, foot separation, and magnetic properties hint at the theory of rising thin flux tubes behind the formation of BMRs and tilt quenching as a possible mechanism for quenching in the Babcock-Leighton dynamo model.