Kavli Affiliate: J. Todd Hoeksema
| First 5 Authors: Lucy W. Will, Lucy W. Will, , ,

| Summary:
Data from the Michelson Doppler Imager (MDI) and Helioseismic and Magnetic Imager (HMI) are analyzed from 1996 to 2023 to investigate tilt angles ($γ$) of bipolar magnetic regions and Joy’s Law for Cycles 23, 24, and a portion of 25. The HMI radial magnetic field ($B_r$) and MDI magnetogram ($B_los$) data are used to calculate ($γ$) using the flux-weighted centroids of the positive and negative polarities. Each active region (AR) is only sampled once. The analysis includes only Beta ($β$)-class active regions since computing $γ$ of complex active regions is less meaningful. During the emergence of the ARs, we find that the average tilt angle ($barγ$) increases from 3.30$^circpm$0.75 when 20% of the flux has emerged to 6.79$^circpm$0.66 when the ARs are at their maximum flux. Cycle 24 had a larger average tilt $barγ_24$=6.67$pm$0.66 than Cycle 23, $barγ_23$=5.11$pm$0.61. No significant difference is found in the slope of Joy’s law or $barγ$ when sampling the ARs at the time of maximum flux or central meridian crossing. There are persistent differences in $barγ$ in the hemispheres, with the southern hemisphere having higher $barγ$ in Cycles 23 and 24, but the uncertainties are such that these differences are not statistically significant.
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