Predicting maximum sunspot number in solar cycle 24

Abstract

A few prediction methods have been developed based on the precursor technique which is found to be successful for forecasting the solar activity. Considering the geomagnetic activity aa indices during the descending phase of the preceding solar cycle as the precursor, we predict the maximum amplitude of annual mean sunspot number in cycle 24 to be 111 ± 21. This suggests that the maximum amplitude of the upcoming cycle 24 will be less than cycles 21-22. Further, we have estimated the annual mean geomagnetic activity aa index for the solar maximum year in cycle 24 to be 20.6 ± 4.7 and the average of the annual mean sunspot num- ber during the descending phase of cycle 24 is estimated to be 48 ± 16.8. Predictions of solar and geomagnetic activities are important for various purposes, including the operation of low-earth orbiting satellites, operation of power grids on Earth, and satellite communication systems. Various techniques, namely, even/odd behaviour, precursor, spectral, climatology, recent climatology, neural networks have been used in the past for the prediction of solar activity. Many investigators (Ohl 1966; Kane 1978, 2007; Thompson 1993; Jain 1997; Hathaway & Wilson 2006) have used the 'precursor' technique to forecast the solar activity. Ohl (1966) noted that the geomagnetic activity in the declining phase of a sunspot cycle is found to be well correlated with the sunspot maximum of the next cycle. Using the geomagnetic activity aa index as the precursor, Jain (1997) predicted the maximum annual mean sunspot number for cycle 23 to be 166.2 which is found to be higher than the observed value of 120. In fact, he did not propose the error estimate in the predicted number otherwise it could have been within error limits. In this view, we predict the maximum amplitude of solar cycle 24 using the pre- cursor technique described by Jain (1997) in this paper. Section 2 describes about the acquisition of data of annual mean sunspot number and the geomagnetic activity aa index used in the current investigation. In section 3, we explain the analysis and results obtained. We briefly discuss and conclude our results in section 4 in the light of other investigations.