Peculiar behaviour of solar cycle-23 in comparison to previous solar cycles

Abstract

The abrupt decrease in cosmic ray intensity and disturbances in geomagnetic field are known as Forbush decreases (FDs) and Geomagnetic storms (GSs) respectively. We have selected the number of FDs and GSs during solar cycles 20–23. It is found that the occurrence of FDs follows the sunspot cycle 23, whereas the occurrence of GSs does not follow the sunspot cycle during the descending phase of solar cycle 23. The event of FDs has been observed to occur more in odd solar cycles in comparison to even solar cycles which show the even–odd asymmetry, whereas the occurrence of GSs increases with the progress of solar cycles from cycle 20–23. Similarly the grouped solar flare (GSF), solar flare index (SFI), bright solar flare and type II solar radio emission are positively correlated with sunspot cycles 20–23 whereas, the halo coronal mass ejections and type IV SREs show their peculiar behaviour in the descending phase of sunspot cycle 23. The occurrence of type IV SREs shows the even–odd asymmetry, whereas type II SREs increases with the progress of solar cycles. The sunspot number, GSF, SFI decreases as the solar cycle progresses from 20 to 23. In the present paper, the contradictory behaviour of FDs and GSs during cycle 23 has been presented in relation to solar parameters.