Abstract Details

Name: Bibhuti Kumar Jha
Affiliation: Indian Institute of Astrophysics
Conference ID: ASI2020_251
Title : Magnetic field dependence of bipolar magnetic region tilts on the Sun: Evidence of tilt quenching
Authors and Co-Authors : Bibhuti Kumar Jha, Bidya Binay Karak, Sudip Mandal and Dipankar Banerjee
Abstract Type : Oral
Abstract Category : Sun and the Solar System
Abstract : The tilt of the bipolar magnetic region (BMR) is crucial in the Babcock--Leighton process for the generation of the poloidal magnetic field in the Sun. Based on the thin flux tube model of the BMR formation, the tilt is believed to be caused by the Coriolis force acting on the rising flux tube of the strong toroidal magnetic field from the base of the convection zone. In this Letter, we analyze the magnetic field dependence of BMR tilts using the magnetograms of Michelson Doppler Imager (MDI) (1996-2011) and Helioseismic and Magnetic Imager} (HMI) (2010--2018). We observe that the distribution of the maximum magnetic field (B_max) of BMRs is bimodal. Its first peak at the low field corresponds to BMRs which do not have sunspots as counterparts in the white light images, whereas the second peak corresponds to sunspots as recorded in both types of images. We find that the slope of Joy's law (gamma_0) initially increases slowly with the increase of B_max. However, when B_max >= 1.5kG, gamma_0 decreases rapidly. The scatter of BMR tilt around Joy's law systematically decreases with the increase of B_max. The decrease of observed gamma_0 with B_max suggests a nonlinear tilt quenching in the Babcock--Leighton process and thus provides a potential candidate for the stability of magnetic field growth in kinematic Babcock-Leighton type dynamo models. Our results of magnetic field dependence of BMR tilt are in general agreement with the thin flux tube model.