Effects of Frontal and Inclined Interplanetary Shocks on High-latitude Field-aligned Currents Response

Abstract:

We investigate by means of a superposed epoch analysis the effects of interplanetary (IP) shocks with different impact angles on high-latitude field-aligned currents (FACs). IP shock impact angle is defined in terms of the shock orientation in relation to the Sun-Earth line. Previous studies with simulations and observations show that frontal shocks tend to be more geoeffective in terms of FACs, cross-polar cap potential, auroral precipitation and so on. We select forty-seven events with almost frontal shocks and 47 events with inclined shocks between 2010 and 2017 from the shock list provided by Oliveira et al. (2018). The zero-epoch time is the shock/compression onset time. Optimally-interpreted FAC distributions during three hours before and after the zero-epoch time are derived from the Iridium magnetic perturbation data made available through the NSF-funded Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) program. Total FACs are also calculated to show the response in FACs quantitatively. Almost frontal shock events show stronger and step-like increase in total FACs compared to weaker and more gradual increase for inclined shock events in both hemispheres. For different local times, we found the difference in FAC response to be most apparent for dayside cusp region currents. For forecasting applications, it appears that shock orientation could be useful knowledge for estimating storm effects.