Analysis on the Temporal-Spatial Distribution of the Geomagnetic Activity Index Vr

Based on the analysis of the Vr index from data from geomagnetic observatories in China and four geomagnetic observatories abroad, temporal-spatial distribution characteristics of Vr index were analyzed. The Vr index showed 27-day solar-cycle recurrences and significant seasonal variation. It also increased with latitude. Meanwhile, both local-time dependence and an obvious dusk-dawn asymmetry existed, which might be related to the asymmetric ring current, the partial ring current, and the field-aligned current.