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Polar Faculae in Solar Cycles 24 and 25

Presentation #102.06 in the session Solar Cycle.

Published onSep 18, 2023
Polar Faculae in Solar Cycles 24 and 25

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 degrees 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 to study the evolution of polar conditions throughout the solar cycle from the ecliptic. We present a new automated method of counting 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 from data averaged over each hour throughout the day for the months of March and September. This averaging improves the contrast of the faculae. Our results show a variation that is similar to that of the Debrechen data when they overlap and extends the time series to March 2023. As we are approaching the predicted maximum of Solar Cycle 25, we should be seeing the number of polar faculae start dropping close to zero.

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