Deciphering Solar Magnetic Activity. II. The Solar Cycle Clock and the Onset of Solar Minimum Conditions

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2012.15186.pdf (4.94 MB)

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Robert Leamon, Scott McIntosh, Sandra Chapman, Nicholas Watkins, Subhamoy Chatterjee and Alan Title, Deciphering Solar Magnetic Activity. II. The Solar Cycle Clock and the Onset of Solar Minimum Conditions, https://arxiv.org/abs/2012.15186

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Abstract

The Sun's variability is controlled by the progression and interaction of the magnetized systems that form the 22-year magnetic activity cycle (the "Hale Cycle") as they march from their origin at ∼55 degrees latitude to the equator, over ∼19 years. We will discuss the end point of that progression, dubbed "terminator" events, and our means of diagnosing them. Based on the terminations of Hale Magnetic Cycles, we construct a new solar activity "clock" which maps all solar magnetic activity onto a single normalized epoch. The Terminators appear at phase 0∗2π on this clock (by definition), then solar polar field reversals commence at 0.2∗2π, and the geomagnetically quiet intervals centered around solar minimum, start at 0.6∗2π and end at the terminator, lasting 40% of the normalized cycle length. With this onset of quiescence, dubbed a "pre-terminator," the Sun shows a radical reduction in active region complexity and (like the terminator events) is associated with the time when the solar radio flux crosses F10.7=90 sfu -- effectively marking the commencement of solar minimum conditions. In this paper we use the terminator-based clock to illustrate a range of phenomena associated with the pre-terminator "event" that further emphasize the strong interaction of the global-scale magnetic systems of the Hale Cycle.