Solar Anti-Hale Bipolar Magnetic Regions: A Distinct Population with Systematic Properties

TL;DR

This study analyzes the tilt and distribution of Hale and anti-Hale bipolar magnetic regions over four solar cycles, revealing that anti-Hale regions form a distinct population likely originating from the same toroidal flux system as Hale regions.

Contribution

It provides the first detailed statistical comparison of Hale and anti-Hale regions' tilt properties, suggesting a common origin within the solar interior's magnetic flux system.

Findings

Anti-Hale regions are a separate population from Hale regions.

Anti-Hale regions have similar tilt properties to Hale regions.

Both types show similar latitudinal distributions.

Abstract

Besides their causal connection with long and short-term magnetic variability, solar bipolar magnetic regions are our chief source of insight into the location, size, and properties of large-scale toroidal magnetic structures in the solar interior. The great majority of these regions (~95%) follow a systematic east-west polarity orientation (Hale's law) that reverses in opposite hemispheres and across even and odd cycles. These regions also present a systematic north-south polarity orientation (Joy's law) that helps build the poloidal field that seeds the new cycle. Exceptions to Hale's law are rare and difficult to study due to their low numbers. Here, we present a statistical analysis of the inclination (tilt) with respect to the equator of Hale versus anti-Hale regions spanning four solar cycles, considering two complementary tilt definitions adopted in previous studies. Our results show that anti-Hale regions belong to a separate population than Hale regions, suggesting a different originating mechanism. However, we find that anti-Hale region tilts present similar systematic tilt properties and similar latitudinal distributions to Hale regions, implying a strong connection between the two. We see this as evidence that they belong to a common toroidal flux system. We speculate that anti-Hale regions originate from poloidal field sheared and strengthened on the spot after the emergence of Hale regions with very strong poloidal contribution. Thus, they are not in contradiction with the idea of largely coherent toroidal flux systems inside the solar interior.