The Hale Cycle Clock

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 $\sim$55 degrees latitude to the equator, over some 19 years. We will discuss the end point of that progression, dubbed ``terminator'' events [McIntosh et al. 2019], and our means of diagnosing them [McIntosh et al. 2019, Leamon et al., 2020]. Based on these terminations of Hale Magnetic Cycles, we construct a new solar cycle phase clock which maps all solar magnetic activity onto a single normalized epoch [Chapman et al, 2020]. If the Terminators appear at phase $0 * 2\pi$, then solar polar field reversals occur at $\sim${}$0.2 * 2\pi$, and the geomagnetically quiet intervals centered around solar minimum, which start at $0.6 * 2\pi$ and end at the terminator are thus 40\% of the normalized cycle. These ``pre-terminators'' show a radical reduction of complexity of active regions and (like the terminators) are well approximated by the time when the solar radio flux, F10.7=90 sfu.

There is thus immediate applicability for the Hale Cycle Clock to predict when the first and last X-flares and other severe Space Weather events of Cycle 25 will be (with the first possibly already happening before the meeting), and we further will discuss the applicability for confirming the length of Cycle 25 as early as its polar field reversal near maximum.

McIntosh et al., "What the Sudden Death of Solar Cycles Can Tell Us About the Nature of the Solar Interior," Solar Physics 294, 88 (2020)

Leamon et al., "Timing Terminators: Forecasting Sunspot Cycle 25 Onset," Solar Physics 295, 36 (2020)

Chapman et al., "Quantifying the Solar Cycle Modulation of Extreme Space Weather," GRL 47, 87795 (2020)