Automated detection and analysis of coronal active region structures across solar cycle 24

Abstract

Observations from NASA’s Solar Dynamic Observatory Atmospheric Imaging Assembly were employed to investigate targeted physical properties of coronal active region structures across the majority of solar cycle 24 (From 2010 May to end of 2020 December). This is the largest consistent study to date which analyses emergent trends in structural width, location, and occurrence rate by performing an automatic and long-term examination of observable coronal and chromospheric limb features within equatorial active region belts across four extreme ultraviolet wavelengths (171, 193, 211, and 304 Å). This has resulted in over 30 000 observed coronal structures and hence allows for the production of spatial and temporal distributions focused upon the rise, peak, and decay activity phases of solar cycle 24. Employing a self-organized-criticality approach as a descriptor of coronal structure formation, power-law slopes of structural widths versus frequency are determined, ranging from -1.6 to -3.3 with variations of up to 0.7 found between differing periods of the solar cycle, compared to a predicted Fractal Diffusive Self-Organized Criticality (FD-SOC) value of -1.5. The North–South hemispheric asymmetry of these structures was also examined with the Northern hemisphere exhibiting activity that is peaking earlier and decaying slower than the Southern hemisphere, with a characteristic ‘butterfly’ pattern of coronal structures detected. This represents the first survey of coronal structures performed across an entire solar cycle, demonstrating new techniques available to examine the composition of the corona by latitude in varying wavelengths.