Journal of Physical Studies 27(3), Article 3901 [5 pages] (2023)
DOI: https://doi.org/10.30970/jps.27.3901

# THE OPTIMAL INTERVAL FOR DETERMINING THE GROWTH RATE OF SOLAR ACTIVITY FOR THE PREDICTION OF THE 25th CYCLE

V. M. Efimenko , V. G. Lozitsky

Astronomical Observatory of the Taras Shevchenko National University of Kyiv, Ukraine

Received 24 July 2023; in final form 12 August 2023; accepted 18 August 2023; published online 04 September 2023

Based on the data on 24 previous solar cycles, the statistical relationship between the rate of increase in the number of sunspots in the initial phase of the growth curve (up to the 35th month from the beginning of the cycle) and the amplitude of the cycle was analyzed. It was found that the maximum smoothed number of sunspots for the 25th cycle depends on the interval used to determine the rate of increase in the sunspot number during the growth phase of the cycle. From our analysis it follows that the amplitude of the 25th cycle will be in the range $W_{\rm max}(25) ≈ 140-170$ units. At the same time, the statistical estimate of the deviation of the points from the linear dependence (Pearson's test) is $r = 0.35-0.91$; the maximum value, $r = 0.91$, was found for the interval of 11 to 35 months. The amplitude of the 25th cycle was also evaluated taking into account the rate of decline in the activity of the previous cycle; this method gives $W_{\rm max}$(25) $≈$ 150 units ($r = 0.73$), which is in good agreement with the forecast based on the growing phase of the cycles. The statistical dependence of the duration of the growth phase of the cycle on the rate of increase in the number of sunspots was analyzed. From this dependence we can conclude that the maximum of the 25th cycle is expected between November 2024 and January 2025.

Key words: Sun, solar activity, number of sunspots, forecasts, maximum of the 25th cycle.

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