Solar activity parameters and their interrelationship: Continuous decrease in flare activity from solar cycles 20 to 23

Abstract

The paper gives an insight regarding the interrelationship among a variety of solar activity (SA) parameters. A detailed correlative study has been performed using the monthly data of various solar activity parameters, for example, sunspot numbers (SSN), solar flux (SF, 10.7 cm), grouped solar flares (GSF), solar flare index (SFI), coronal index (CI), and tilt angle (TA) for the solar cycles 19 to 23, the present cycle. Though in general SSN shows a high degree of correlation with other SA parameters, the relationship between SSN and flare indices (GSF and SFI) is not straightforward. The slope of the regression lines between SSN and GSF (for cycles 20 to 23) and those between SSN and SFI (for cycles 21 to 23) is found to decrease continuously with the progression of cycles, without any associated unidirectional change in the correlation coefficient between these indices. In conformity, the similar feature is also observed from the peak values of SSN and flare indices. It is not seen, however, in the case of other SA parameters. The different trend of regression lines between SSN-GSF and SSN-SFI has been explained on the basis of the duration of the major solar flares. The present analysis also includes the statistical/numerical investigations of the occurrence of flares (imp ≥ IB) over the span of solar cycles 20 to 23. These findings shed new light on the underlying physical processes responsible for solar activity and their generic relationship. Copyright 2007 by the American Geophysical Union.