Solar and Interplanetary Causes of Magnetic Cloud Related Forbush Decreases During Solar Cycle 23,24

Magnetic cloud related Forbush decreases ≥3% observed at Oulu super Neutron monitor during solar cycle 23and 24 with coronal mass ejections, geomagnetic storms and interplanetary magnetic fields have been studied. 82 Fds of defined criteria, out of which 72 (87.81%) have been determined and found to be associated with coronal mass ejections. A positive correlation with correlation coefficient 0.56 between magnitude of magnetic cloud related Fds and speed of associated CMEs has been observed. Further ,76 (92.69%) Forbush decreases associated with geomagnetic storms and magnitudes of Forbush decreases have been obtained. Magnitude associated geomagnetic storms show positive co-relation with correlation coefficient 0.59. The interplanetary magnetic field disturbances are also closely associated with Fds and 82 (100%) Forbush decreases (Fds) have been found to be associated with disturbances, in interplanetary (JIMF). There is positive correlation between magnitude of magnetic cloud related Forbush decreases (Fds) and magnitude of disturbances in IMF events. Statistically calculated co-relation co-efficient is 0.35 between these two events.
Keywords: – Forbush Decreases, Coronal Mass Ejections, Magnetic Clouds and Interplanetary Magnetic Fields.

Anita Shukla1, Dhanraj2*