Spotless days and geomagnetic index as the predictors of solar cycle 25

TL;DR

This study predicts the amplitude and timing of solar cycle 25 using spotless days and geomagnetic activity, finding both predictors suggest a weaker cycle than cycle 24 and estimating its peak around early 2024.

Contribution

It introduces spotless days as a new predictor for solar cycle amplitude, alongside geomagnetic indices, enhancing prediction methods for solar activity.

Findings

Cycle 25 will likely be weaker than cycle 24.

Peak of cycle 25 expected between February and March 2024.

Spotless days are a viable predictor for solar cycle characteristics.

Abstract

We study the sunspot activity in relation to spotless days (SLDs) during the descending phase of solar cycle $11$--$24$ to predict the amplitude of sunspot cycle $25$. For this purpose, in addition to SLD, we also use the geomagnetic activity (aa index) during the descending phase of a given cycle. A very strong correlation of the SLD (R=$0.68$) and aa index (R=$0.86$) during the descending phase of a given cycle with the maximum amplitude of next solar cycle has been estimated.The empirical relationship led us to deduce the amplitude of cycle $25$ to be 99.13$\pm$ 14.97 and 104.23$\pm$ 17.35 using SLD and aa index, respectively as predictors.Both the predictors provide comparable amplitude for solar cycle $25$ and reveal that the solar cycle $25$ will be weaker than cycle $24$. Further we derive that the maximum of cycle $25$ is likely to occur between February and March 2024. While the aa index has been used extensively in the past, this work establishes SLDs as another potential candidate for predicting the characteristics of the next cycle.