Polar Faculae and the Polar Magnetic Field in Solar Cycles 24 and 25

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Abstract

Polar faculae are footprints of the polar magnetic field that are visible as bright spots along intergranular lanes. Unlike equatorial faculae and sunspots, which are found at low to moderate solar latitudes and peak in number at solar maximum, polar faculae are found at latitudes greater than $70^\circ$ and peak in number around solar minimum. Polar faculae tend to have the same magnetic polarity as the general polar magnetic field, and their number has been shown to correlate with the strength of that magnetic field. This makes them good candidates for studying the evolution of polar conditions throughout the solar cycle from the ecliptic. We present a new automated method for counting and studying polar faculae in Helioseismic and Magnetic Imager (HMI) Ic\_720s data using a source detection function from the Python library Photutils. We applied this method to both polar regions, using data averaged over each hour throughout the day between 2010 and 2022, the period for which HMI data is available in HelioCloud. Our results show a variation that is similar to that of the faculae count data from the Debrecen Heliophysical Observatory when they overlap, and extends that time series to December 2022. We also found that the magnetic field of the polar faculae averaged over the polar cap has the same polarity as the polar magnetic field from other measurements. However, we show that faculae with both polarities are present throughout the sunspot cycle. This indicates that the solar dynamo does not destroy the polar field in a single event but uses a stochastic process.

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