A Systematic Study of Hale and Anti-Hale Sunspot Physical Parameters

Abstract

We present a systematic study of sunspot physical parameters using full disk magnetograms from MDI/SoHO and HMI/SDO. Our aim is to use uniform datasets and analysis procedures to characterize the sunspots, paying particular attention to the differences and similarities between "Hale" and "anti-Hale" spots. Included are measurements of the magnetic tilt angles, areas, fluxes and polarity pole separations for 4385 sunspot groups in Cycles 23 and 24 each measured, on average, at $\sim$66 epochs centered on meridian-crossing. The sunspots are classified as either "Hale" or "anti-Hale", depending on whether their polarities align or anti-align with Hale's hemispheric polarity rule. We find that (1) The "anti-Hale" sunspots constitute a fraction ($8.1\pm 0.4$)\% of all sunspots, and this fraction is the same in both hemispheres and cycles, (2) "Hale" sunspots obey Joy's law in both hemispheres and cycles but "anti-Hale" sunspots do not. Three equivalent forms of Joy's law are derived, $\sin \gamma =(0.38\pm 0.05)\sin \varphi$, $\gamma =(0.39\pm 0.06)\varphi$, and $\gamma =(23.80\pm 3.51)\sin \varphi$, where $\gamma$ is the tilt angle and $\varphi$ is the heliospheric latitude, (3) The average Hale sunspot tilt angle is $\overline{\gamma }=5.49^{\circ }\pm 0.09$, (4) The tilt angles, magnetic fluxes and pole separations of sunspots are interrelated, with larger fluxes correlated with larger pole separations and smaller tilt angles. We present empirical relations between these quantities. Cycle 24 is a much weaker cycle than Cycle 23 in sunspot numbers, cumulative magnetic flux, and average sunspot magnetic flux. The "anti-Hale" sunspots are also much weaker than "Hale" sunspots in those parameters, but they share similar magnetic flux distributions and average latitudes. We characterize the two populations, and aim to shed light on the origin of "anti-Hale" sunspots.

14 Figures, 6 Tables, Accepted by ApJ

References in corpus (5)

• Magnetic Flux Transport at the Solar Surface
• Magnetic Field Confinement in the Corona: The Role of Magnetic Helicity Accumulation
• Re-examining Sunspot Tilt Angle to Include Anti-Hale Statistics
• Tilt of sunspot bipoles in Solar Cycles 15 to 24
• How many active regions are necessary to predict the solar dipole moment?

Cited by in corpus (13)

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• Improved AI-generated Solar Farside Magnetograms by STEREO and SDO Data Sets and Their Release
• Solar Anti-Hale Bipolar Magnetic Regions: A Distinct Population with Systematic Properties
• Impact of Anomalous Active Regions on the Large-scale Magnetic Field of the Sun
• Evolution of the Sun's Polar-fields and the Poleward Transport of Remnant Magnetic Flux
• A Catalog of Bipolar Active Regions Violating the Hale Polarity Law, 1989-2018
• Exploring Bistability in the Cycles of the Solar Dynamo through Global Simulations
• Synthetic solar cycle for active regions violating the Hale's polarity law
• Naked emergence of an anti-Hale active region I. Overall evolution and magnetic properties
• Characterizing the Umbral Magnetic Knots of $\delta$-Sunspots
• Extreme Fluctuations in the Sun's Activity over the Modern Maximum: Understanding the Enigmatic Solar Cycles 19-20
• Observation-Based Iterative Map for Solar Cycles. I. Nature of Solar Cycle Variability
• Relationship Between the Tilt Angle of Sunspot Group and the Properties of the Next Solar Cycle