Understanding Forbush decrease drivers based on shock-only and CME-only models using global signature of February 14, 1978 event

摘要

We have studied Forbush decrease (FD) event occurred on February 14, 1978using 43 neutron monitor observatories to understand the global signature ofFD. We have studied rigidity dependence of shock amplitude and total FDamplitude. We have found almost the same power law index for both shock phaseamplitude and total FD amplitude. Local time variation of shock phase amplitudeand maximum depression time of FD have been investigated which indicatepossible effect of shock/CME orientation. We have analyzed rigidity dependenceof time constants of two phase recovery. Time constants of slow component ofrecovery phase show rigidity dependence and implies possible effect ofdiffusion. Solar wind speed was observed to be well correlated with slowcomponent of FD recovery phase. This indicates solar wind speed as possibledriver of recovery phase. To investigate the contribution of interplanetarydrivers, shock and CME in FD, we have used shock-only and CME-only models. Wehave applied these models separately to shock phase and main phase amplitudesrespectively. This confirms present accepted physical scenario that the firststep of FD is due to propagating shock barrier and second step is due to fluxrope of CME/magnetic cloud.