Timing Terminators: Forecasting Sunspot Cycle 25 Onset

Abstract

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Overlapping Magnetic Activity Cycles and the Sunspot Number: Forecasting Sunspot Cycle 25 Amplitude

“…Removing the smoothed sunspot trend from the monthly and 12-month smoothed timeseries results in the timeseries shown in Figure 3b. In Leamon et al (2020) we apply the discrete Hilbert transform to the two sunspot trend-subtracted timeseries The predicted terminator separation for SC24 is shown in both panels, which along with the regression line results in a prediction for the amplitude of SC25 in panel (b) that is significantly higher than the consensus prediction of the SC25PP (magenta bar). The black horizontal line in the top panel is the mean of the SSN maximum, while the dashed and dotted blue lines in the bottom panel are the 68% and 95% prediction interval boundaries for the SC25 prediction, respectively.…”

“…Performing a discrete Hilbert transform analysis and terminator identification (see Leamon et al, 2020) but with the monthly (as opposed to daily) sunspot record and with the subtraction of a slowly time-varying trend as shown in panel a of Figure 3, permits the expansion of the terminator timeseries back to 1749. Indeed, such an analysis covers the Dalton minimum (from 1790 to 1830, or SC5 through SC7) in addition to the epochs of high activity in the late 1700s, 1850s and 1950s.…”

“…We use the method discussed in Chapman et al (2020) and Leamon et al (2020) to determine our evaluation of the terminator dates via the analytic phase of the discrete Hilbert transform. For a given finite segment of a time series, the discrete Hilbert transform yields a difference in analytic phase relative to that at some (arbitrary) start time.…”

“…M2019 extended that analysis back another century such that 13 sunspot cycles had their terminator events identified-see the vertical blue dashed lines in Figure 3 and Table 1. Following M2019, Leamon et al (2020) explored an algorithmic approach to the identification of termination events in sunspot and activity proxy data. This was achieved by exploiting the properties of the discrete Hilbert transform (Marple, 1999).…”

Quantifying the Solar Cycle Modulation of Extreme Space Weather

“…The sunspot number analytic phase can in principle be extrapolated forward in time, albeit with some uncertainty, to forecast when a specific phase will occur. This has been done for the terminator at the start of the next solar cycle (Leamon et al, 2020), and a similar procedure could also forecast when the “switch off” of activity will occur.…”