The persistence of solar activity indicators and the descent of the Sun into Maunder Minimum conditions

[1] The recent low and prolonged minimum of the solar cycle, along with the slow growth in activity of the new cycle, has led to suggestions that the Sun is entering a Grand Solar Minimum (GSMi), potentially as deep as the Maunder Minimum (MM). This raises questions about the persistence and predictability of solar activity. We study the autocorrelation functions and predictability R²_L(t) of solar indices, particularly group sunspot number R_G and heliospheric modulation potential Φ for which we have data during the descent into the MM. For R_G and Φ, R²_L(t) > 0.5 for times into the future of t ≈ 4 and ≈ 3 solar cycles, respectively: sufficient to allow prediction of a GSMi onset. The lower predictability of sunspot number R_Z is discussed. The current declines in peak and mean R_G are the largest since the onset of the MM and exceed those around 1800 which failed to initiate a GSMi.