A new field-aligned current index AF and its relation to the storm-time ring current and energetic neutral atom (ENA) emissions

Abstract

It is shown that a newly devised field-aligned current index AF is well correlated with the Dst index, the correlation coefficient being 0.93. The AF index is based on the fact that geomagnetic Y (or D) component variations in the middle and low latitudes are mainly caused by field-aligned currents. It is also demonstrated that energetic neutral atom (ENA) emissions measured by the Geotail satellite are well correlated with the AF index.