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Two new methods for counting and tracking the evolution of polar faculae

Presentation #113.02 in the session “Solar Physics Division (SPD): Photosphere & Chromosphere, Solar Interior, and Solar Cycle”.

Published onJun 18, 2021
Two new methods for counting and tracking the evolution of polar faculae

Polar Faculae are the unipolar footpoints of field lines near the sun’s poles and are visible as bright points on the edges of granules. Their number has been shown to correlate with the strength of the polar magnetic field, and therefore better understanding polar faculae enables better understanding of the polar magnetic field and its evolution, as well as conditions and convective motions at the poles. We present two methods of tracking faculae. In one the standard deviation of HMI continuum intensity images is calculated over a day and the facular candidates identified by their trails. The other overlays images of the progressive standard deviation over the course of the day with individual HMI magnetograms to show the close relationship between the facular candidates and the magnetic field. We apply this method to one pole each day for a week every 6 months, beginning September 2010. Our results confirm that faculae track regions of unipolar magnetic field that match the polarity of the visible pole. We observe the motion of the faculae and distinguish between motion due to the sun’s rotation and “proper motion” due to faculae moving on the sun’s surface, confirming that faculae participate in convective motions at the poles. This method provides a larger daily count of faculae than previous studies, allowing for a valid statistical determination of the facular lifetime. We show that the lifetime has a mode of 1-3 hours, with some faculae lasting up to 10 hours.

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