State of the inner heliosphere as given by the G index of interplanetary scintillation and the Dst index of geomagnetic activity

In the study of the impact of solar activity on the terrestrial magnetosphere, the interplanetary medium plays a major role. The purpose of this work is to analyze a global index of interplanetary scintillation, G, obtained from the g maps of Cambridge Observatory, UK, in relation to the geomagnetic index Dst, to determine the possible impact of both large‐scale events and small magnetic irregularities on the magnetosphere of our planet. The analysis consists of the comparison of the two time series G and Dst for the period 1991–1994. It is found that in 94% of the cases when the Dst index falls to less than −70 nT, the G index presents a positive anomaly. Furthermore, the cross correlation shows that there is a marked anticorrelation with a lag of 2 days. A superposed epoch analysis is also performed for −10 to 10 days around the occurrence of 16 of the events in the period showing a peak at day zero of 2.93 sigmas that start 2 days before. No peak was found when the analysis was performed on 16 randomly chosen dates in the period. The results indicate that the state of the inner heliosphere as given by the G index may be important in the study of the solar wind related magnetospheric activity.