Bibhuti Kumar Jha

NameBibhuti Kumar Jha
AffiliationAryabhatta Research Institute of Observational Sciences, Nainital
TitleSignature of Quenching from Observation of Tilted Bipolar Magnetic Regions on the Sun
AuthorsBibhuti Kumar Jha, Bidya Binay Karak, Sudip Mandal and Dipankar Banerjee
AbstractIn the Babcock–Leighton process the tilt of bipolar magnetic region (BMR) play a key role for the generation of the poloidal magnetic field in Sun. In 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 field from the base of the convection zone (BCZ). Here in this work we analyze the magnetic field dependence of BMR tilts using the magnetograms of MDI (1996–2011) and HMI (2010–2018). We observe that the distribution of the maximum magnetic field (Bmax) 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 BMRs which have sunspots as counterparts. We find that the slope of Joy’s law ($\gamma_0$) initially increases slowly with the increase of Bmax. However, when Bmax $\ge$ 2 kG, $\gamma_0$ decreases. Scatter of BMR tilt around Joy’s law systematically decreases with the increase of Bmax. In the white-light digitized data from Kodaiknala Solar Observatory (1923-2011), where we have used sunspot area as a proxy of magnetic field and we find a similar behaviour. This further verify our findings from magnetogram data. The decrease of observed $\gamma_0$ with Bmax provides a hint to a nonlinear tilt quenching in the Babcock–Leighton process. We finally discuss how our results may be used to make a connection with the thin flux tube model.