The Magnetic Classification of Solar Active Regions 1992 - 2015

Abstract

The purpose of this letter is to address a blind-spot in our knowledge of solar active region statistics. To the best of our knowledge there are no published results showing the variation of the Mount Wilson magnetic classifications as a function of solar cycle based on modern observations. We show statistics for all active regions reported in the daily Solar Region Summary from 1992 January 1 to 2015 December 31. We find that the $\alpha$ and $\beta$ class active regions (including all sub-groups e.g. $\beta \gamma$, $\beta \delta$) make up fractions of approximately 20% and 80% of the sample respectively. This fraction is relatively constant during high levels of activity, however, an increase in the $\alpha$ fraction to about 35% and and a decrease in the $\beta$ fraction to about 65% can be seen near each solar minimum and is statistically significant at the 2-$\sigma$ level. Over 30% of all active regions observed during the years of solar maxima were appended with the classifications $\gamma$ and/or $\delta$, while these classifications account for only a fraction of a percent during the years near the solar minima. This variation in the active region types indicates that the formation of complex active regions may be due to the pileup of frequent emergence of magnetic flux during solar maximum, rather than the emergence of complex, monolithic flux structures.

4 figures, 1 table, accepted for publication in ApJL

References in corpus (2)

• The Solar Cycle
• $\delta$-Sunspot Formation in Simulation of Active-Region-Scale Flux Emergence

Cited by in corpus (23)

• Flare-productive active regions
• Numerical Simulations of Flare-productive Active Regions: delta-sunspots, Sheared Polarity Inversion Lines, Energy Storage, and Predictions
• 3He-Rich Solar Energetic Particles from Sunspot Jets
• Statistical Signatures of Nanoflare Activity. I. Monte Carlo Simulations and Parameter-space Exploration
• A Framework for Designing and Evaluating Solar Flare Forecasting Systems
• Different contributions to space weather and space climate from different big solar active regions
• Differences in the solar cycle variability of simple and complex active regions during 1996-2018
• Bihelical spectrum of solar magnetic helicity and its evolution
• Solar Flares Forecasting Using Time Series and Extreme Gradient Boosting Ensembles
• Towards a live homogeneous database of solar active regions based on SOHO/MDI and SDO/HMI synoptic magnetograms. I. Automatic detection and calibration
• Magnetic fluxes of solar active regions of different magneto-morphological classes: I. Cyclic variations
• Solar observations with single-dish INAF radio telescopes: continuum imaging in the 18-26 GHz range
• How rare are counter Evershed flows?
• Active-Region Tilt Angles from White-Light Images and Magnetograms: The Role of Magnetic Tongues
• Inferring Line-of-Sight Velocities and Doppler Widths from Stokes Profiles of GST/NIRIS Using Stacked Deep Neural Networks
• Statistical Study of the Correlation between Solar Energetic Particles and Properties of Active Regions
• Characterizing the Umbral Magnetic Knots of $\delta$-Sunspots
• A prolific solar flare factory. Nearly continuous monitoring of an active region nest with Solar Orbiter
• Near-continuous tracking of solar active region NOAA 13664 over three solar rotations
• Eigenspectra of solar active region long-period oscillations
• Hemispheric Distribution of Solar Active Regions During Solar Cycles 23-25
• Evaluating Pointing Strategies for Future Solar Flare Missions
• Radio Burst and Circular Polarization Studies of the Solar Corona at Low Frequencies