Maximal growth rate of the ascending phase of a sunspot cycle for predicting its amplitude

TL;DR

This study shows that the maximal growth rate of sunspot activity during the ascending phase of a solar cycle is a reliable predictor of the cycle's amplitude, with hemispheric data improving prediction accuracy.

Contribution

The paper introduces a new predictive method using the maximal growth rate of sunspot activity, especially from hemispheric data, to forecast solar cycle amplitudes more accurately.

Findings

High correlation (up to r=0.93) between predicted and actual cycle amplitudes.

Hemispheric sunspot data improves prediction accuracy by up to 27%.

Predictions can be made 2 to 49 months in advance, averaging 21 months.

Abstract

Forecasting the solar cycle amplitude is important for a better understanding of the solar dynamo as well as for many space weather applications. We demonstrated a steady relationship between the maximal growth rate of sunspot activity in the ascending phase of a cycle and the subsequent cycle amplitude on the basis of four data sets of solar activity indices: total sunspot numbers, hemispheric sunspot numbers from the new catalogue from 1874 onwards, total sunspot areas, and hemispheric sunspot areas. For all the data sets, a linear regression based on the maximal growth rate precursor shows a significant correlation. Validation of predictions for cycles 1-24 shows high correlations between the true and predicted cycle amplitudes reaching r = 0.93 for the total sunspot numbers. The lead time of the predictions varies from 2 to 49 months, with a mean value of 21 months. Furthermore, we demonstrated that the sum of maximal growth rate indicators determined separately for the north and the south hemispheric sunspot numbers provides more accurate predictions than that using total sunspot numbers. The advantages reach 27% and 11% on average in terms of rms and correlation coefficient, respectively. The superior performance is also confirmed with hemispheric sunspot areas with respect to total sunspot areas. The maximal growth rate of sunspot activity in the ascending phase of a solar cycle serves as a reliable precursor of the subsequent cycle amplitude. Furthermore, our findings provide a strong foundation for supporting regular monitoring, recording, and predictions of solar activity with hemispheric sunspot data, which capture the asymmetric behaviour of the solar activity and solar magnetic field and enhance solar cycle prediction methods.