Solar and interplanetary causes of x-class, x-ray solar flare related forbush decreases of higher magnitude in cosmic ray intensity during the period of solar cycle 23 and rising phase of solar cycle 24

Forbush decreases (Fds) of higher magnitude associated with X-Class X-ray solar flares observed during the period of solar cycle 23 and rising phase of 24 (1997-2012) have been studied with solar and interplanetary parameters. It is observed that all the Forbush decreases (Fds) are associated with halo and partial halo coronal mass ejections (CMEs), and most of them (82.35%) are higher speed CMEs with speed >1000Km/s. A large positive correlation with a correlation coefficient of 0.68 has been found between the magnitude of Forbush decreases (Fds) and the speed of associated CMEs. Further, all these Forbush decreases (Fds) have been identified as being associated with fast forward interplanetary shocks and disturbances in solar wind plasma parameters. Positive correlations with correlation coefficient 0.44 and 0.37 have been determined between magnitudes of Forbush decreases (Fds), and peak value and magnitude of associated disturbances in solar wind plasma temperature, 0.32 and 0.42 between the magnitude of Forbush decreases (Fds) and peak value and magnitude of associated disturbances in solar wind plasma density. Positive correlations with correlation coefficient 0.32 have also been determined between magnitudes of Forbush decreases (Fds) and the peak value of associated disturbances in solar wind plasma velocity.