The G Index of Interplanetary Scintillation Data and Its Relation to Forbush Decreases During 1991–1994

The purpose of this work is to analyze a global index of interplanetary scintillation, G, obtained from the g-maps of Cambridge Observatory, UK, and associate it with the occurrence of sudden decreases of the cosmic radiation, known as Forbush decreases (Fds), to determine their possible relation. For this purpose we perform a superposed epoch analysis of the Gindex, with respect to the occurrence of Forbush decreases, registered at Oulu Station, Finland, for the period 1991–1994. We found an increase in the value of Gcoinciding with the occurrence of the Forbush decrease, especially for those events with a fall greater than 10%. We conclude that the G index is a macroscopic parameter representative of the inner structure of the heliosphere, and has bearings on phenomena affecting the Earth's environment, as shown by Forbush decreases and possibly geomagnetic activities.