TWINS ENA Imaging Observations of the Timing of Ring Current Intensification

Intensification of the Earth's ring current is a fundamental element of the dynamic geospace response to solar wind driving. The ring current can contain petaJoules of energy during substorms and storms. The timing of ring current intensification yields information about how changes in the solar wind and interplanetary magnetic field (IMF) propagate from the dayside magnetopause to the nightside inner magnetosphere. Energetic neutral atom (ENA) imaging of the ring current is uniquely well suited to investigate this macroscale day-to-night timing, which would be difficult to obtain routinely with a finite number of in situ spacecraft. In this paper we use 1-minute cadence ENA images from Two Wide-angle Imaging Neutral-atom Spectrometers (TWINS), to study the timing between sudden changes in dayside IMF north-south polarity and subsequent intensifications of the nightside ring current, for several case study events. We compare our results to previous work reporting a delay of tens of minutes between IMF polarity changes and subsequent plasmapause motion.