LONG-TERM VARIATION OF DIFFERENT SOLAR AND GEOMAGNETIC ACTIVITIES

Long-term variations of different solar source activities and large geomagnetic disturbances also termed as geomagnetic storms (GMSs) which are associated with Dst decreases of more than 100 nT, and are observed during the period 1997-2011 have been analysed. It is found that 93 large GMSs falling in our selection criteria. We have established long-term variability of above selected 93 large GMSs with different solar source activities that provides a better aspect to understand the space-weather phenomenon. Long-term variation of sudden storm commencement (SSCs) for solar cycle 21-23 shows that annually occurred value of SSCs follows with sunspot number (SSN) during the period of solar cycle 22 and 23, but solar cycle 21 is exceptional among them. Long-term variation of Kleczek solar flare index (SFI) with annual mean SSN for the period 1976-2007 shows that the yearly occurred value of SFI varies with 11year sunspot cycle. Long-term variation of solar radio flux (SRF) with annual mean SSN for the period 1976-2011, shows that the yearly occurred value of SRF varies with 11-year sunspot cycle as similar as variation of other solar transients. The long-term solar irradiance variations (TSI) have shown that the Sun has a slight cooling trend since 1976. Various space weather condition and climatic change have also been analysed.